2024 Season Summary

The 2024 Atlantic hurricane season was well above average in activity, with a total of

18 cyclones attaining tropical depression status,
18 cyclones attaining tropical storm status,
11 cyclones attaining hurricane status, and
5 cyclones attaining major hurricane status.

Before the beginning of the season, I predicted that there would be

24 cyclones attaining tropical depression status,
22 cyclones attaining tropical storm status,
12 cyclones attaining hurricane status, and
6 cyclones attaining major hurricane status.

The average numbers of tropical storms, hurricanes and major hurricanes (over the 30 year period 1991-2020) were 14.4, 7.2, and 3.2, respectively. The eventual numbers for 2024 fell short of my predictions for a historically active season, but the (preliminary) Accumulated Cyclone Energy value for 2024 was 162, enough to qualify as a "hyperactive" season, since it exceeded 165% of the median for hurricane seasons since 1950. Most predictions for the 2024 season were extremely high due to several favorable pre-season indicators. The main reason the true activity didn't quite reach this ceiling was an anomalous gap in storm formation near peak season; this will be discussed further below.

The most basic requirement for hurricane formation is warm ocean water. 2024 had this in spades.

A majority of the tropical Atlantic, Caribbean, and Gulf of Mexico experienced its warmest hurricane season on record. This is of course part of the worrying trend of climbing ocean temperatures globally due to anthropogenic global warming, but previous recent seasons had also seen very high ocean temperatures. The difference this year was where they were concentrated: the highest anomalies were in the heart of the main formation regions, rather than in the subtropical Atlantic.

During the heart of hurricane season, the average vertical wind shear was the lowest on record; since shear disrupts tropical cyclone formation, this also should contribute to higher activity. Both high ocean temperatures and low wind shear were well anticipated, hence the sky-high forecasts. And indeed, 2024 got off to a roaring start, with Hurricane Beryl became the most powerful hurricane ever recorded so early in a season. After the formation of Ernesto on August 13, however, no more storms were named until September 9, nearly a month-long gap. Since the climatological peak of hurricane season is mid-September, this was very unusual. As a point of comparison, the last time no named storms formed in that span of dates was 1968. After September 9, things switched to high gear again for the rest of hurricane season. For instance, 7 hurricanes formed on or after September 25, the first time this has ever happened on record. What happened in that gap?

A few factors likely contributed, but the main reason was that hurricane activity was cut off at the spigot, in a way: the north African monsoon shifted unusually far north. This caused tropical waves entering the Atlantic to quickly curve rightward into cooler and more stable environments. Meanwhile, dry air and high upper-level atmospheric temperatures over the tropical Atlantic quelled thunderstorm activity, making it difficult for disturbances to gain a foothold on the way to development. In short, tropical cyclone formation is complex; even when a couple factors are extremely favorable, other ingredients are still needed.

The following snapshot on October 6 highlights how busy that month was. Kirk (top right), Leslie (bottom right), and Milton (left) were all hurricanes simultaneously on that day. This was the first time such an occurrence had been recorded in October or later.

As far as more localized predictions go, land impacts were most common around the Gulf of Mexico, while U.S. east coast and greater Antilles impacts were somewhat less than I predicted. Unfortunately, a total of five hurricanes made landfall in the conintental United States, continuing a recent streak of bad hurricane seasons for the country. The most devastating of these was Hurricane Helene, which due to its size and strength caused widespread damage in the U.S. southeast and southern Appalachia, leading to the largest death toll in the mainland U.S. since Hurricane Katrina. Hurricane Milton also caused substantial damage in Florida, and was notable for being the strongest hurricane by minimum pressure since 2005, with a minimum central pressure of 897 mb.

Some other notable facts and figures from 2024 include:

• Beryl became the earliest category 4 and later the earliest category 5 recorded in the Atlantic; it also became the second southermost major hurricane formation, at 10.6° N
• Kirk became the easternmost forming hurricane in the tropical Atlantic after September, at 40.1° W, until this record was crushed immediately after by Leslie at 34.2° W
• Milton strengthened from a tropical depression to a category 5 hurricane in 49 hours, the fastest this had ever been observed
• Rafael was the second ever November major hurricane in the Gulf of Mexico on record

The 2024 hurricane season was very active and damaging, despite slightly underachieving statistically relative to pre-season predictions. Sources: https://yaleclimateconnections.org/2024/12/the-weirdly-hyperactive-2024-atlantic-hurricane-season-ends/, https://newsmediarelations.colostate.edu/2024/11/26/csu-researchers-slightly-over-predict-extremely-active-2024-atlantic-hurricane-season/,

Professor Quibb's Picks – 2024

My personal prediction for the 2024 North Atlantic Hurricane season (written May 28, 2024) is as follows:

24 cyclones attaining tropical depression status,
22 cyclones attaining tropical storm status,
12 cyclones attaining hurricane status, and
6 cyclones attaining major hurricane status.

This prediction far exceeds the 1991-2020 averages of 14.4 tropical storms, 7.2 hurricanes, and 3.2 major hurricanes each season. In short, I expect 2024 to be very active, with a moderate probability of breaking the top 5 most active seasons ever recorded, at least in terms of number of named storms. Below, I'll discuss the various factors that went into making this prediction.

The biggest story of the year so far in hurricane forecasting is the unprecedented warming of the tropical Atlantic ocean. For many decades, climate scientists have documented the increasing ocean temperatures caused by anthropogenic global warming, but 2024 stands out in particular.

The chart above shows the global averaged sea surface temperature since 1981. The second half of 2023 and 2024 thus far have seen average ocean temperatures far above what had been previously observed. On its own, a global ocean temperature increase should correlate to more fuel for tropical cyclone formation, but this isn't all.

The above diagram gives a snapshot from earlier this month of global sea surface temperature anomalies relative to the current mean. This means that the the large positive average anomaly from the previous image is accounted for, and we're looking at deviations from that average. One area that stands out is the tropical Atlantic, which is experiencing unusual warmth on top of an unprecedented global mean. In previous years, I've often commented on warm ocean temperatures and their contribution to more active seasons, but this year's signal is stronger than any I've seen. This factor alone is enough to predict a very active hurricane season.

One other area that stands out in the previous global ocean temperature map is the equitorial eastern Pacific, which is relatively much cooler. This signals the return of La Niña conditions, which have ramifications for global weather.

The chart above is the model forecast of the El Niño Southern Oscillation (ENSO) index, a composite measure of the sea surface temperature anomalies in the equitorial Pacific. Most of 2023 saw a positive index, called El Niño, but the index has recently been dropping, and the official conditions for a La Niña event should be met by peak hurricane season. Typically such an event is correlated with lower wind shear and hence less disruption to developing cyclones. Therefore, this is another signal in favor of an active hurricane season.

I'll run through a few more quick factors. Early indications point to a west African monsoon which is more robust than usual (this is captured, for instance, by the long-term model precipitation forecast above for the three month period August-October 2024). Many hurricanes have their origin in disturbances crossing west Africa, so this could mean that there are more "seeds" for hurricane formation; this is yet another positive factor for an active 2024. Lastly, I often consider the strength of trade winds and the magnitude of zonal wind shear across the Atlantic basin. Roughly, this is a measure of how consistent the direction and strength of the east-west component of wind is at different altitudes in the atmosphere. As mentioned above, La Niña usually leads to lower wind shear, but it's worth noting that these measures have remained close to average for 2024 thus far. This factor therefore doesn't have a significant forecast impact right now.

Next, I'll give a finer analysis of the risks by region. My estimates are on a scale from 1 (least risk) to 5 (most risk).

U.S. East Coast and Atlantic Canada: 5
The east coast of North America is at extreme risk from hurricanes this year. Ocean warmth was already discussed above, but on top of that, the likelihood of La Niña conditions and current model data both point to stronger than usual ridging over the subtropical Atlantic this summer. This means that tropical cyclone tracks have less chance of curving out to sea and an increased risk to land.

Yucatan Peninsula and Central America: 4
The same factors pointing to an active hurricane season suggest an above-normal risk for these regions. However, the predicted shear and atmospheric moisture anomalies aren't quite as favorable in the southern and western Caribbean, so I'll assign a "4" rather than a "5" here.

Carribean Islands: 5
For the last few years, many tropical cyclones forming in the tropical Atlantic had some struggles with dry air and wind shear as they approached the Caribbean; others curved out to sea before impacting the islands. This year, the risk seems much higher: a more robust African monsoon will lead to more long-track hurricanes and ample atmospheric moisture. Further, the developing La Niña will suppress shear and keep storms on a more westward track.

Gulf of Mexico: 4
As with every other region, the coast of the Gulf of Mexico is at high risk. The choice of "4" rather than "5" is due to some expected dryness, especially in the western Gulf where extreme heat and drought may prevail for significant parts of the season. The eastern Gulf should be on high alert, especially near the peak of the season in August and September.

Overall, I expect the 2024 Atlantic hurricane season to be very active, potentially historically so. Nevertheless, this is just an amateur forecast. Individuals in hurricane-prone areas should always have emergency measures in place. For more on hurricane safety sources, see here. Remember, devastating storms can occur even in otherwise quiet seasons.

Sources: https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf, https://tropical.colostate.edu/Forecast/2024-04.pdf, https://www.tropicaltidbits.com/analysis/models/, https://www.noaa.gov/news-release/noaa-predicts-above-normal-2024-atlantic-hurricane-season

Hurricane Names List – 2024

The name list for tropical cyclones forming in the North Atlantic basin for the year 2024 is as follows:

Alberto
Beryl
Chris
Debby
Ernesto
Francine
Gordon
Helene
Isaac
Joyce
Kirk
Leslie
Milton
Nadine
Oscar
Patty
Rafael
Sara
Tony
Valerie
William

This list is the same as that for the 2018 season, with the exception of Francine and Milton, which replaced the retired names Florence and Michael, respectively.

2023 Season Summary

The 2023 Atlantic hurricane season was above average in activity, with a total of

21 cyclones attaining tropical depression status,
20 cyclones attaining tropical storm status,
7 cyclones attaining hurricane status, and
3 cyclones attaining major hurricane status.

Before the beginning of the season, I predicted that there would be

15 cyclones attaining tropical depression status,
14 cyclones attaining tropical storm status,
8 cyclones attaining hurricane status, and
4 cyclones attaining major hurricane status.

The average numbers of tropical storms, hurricanes and major hurricanes (over the 30 year period 1991-2020) were 14.4, 7.2, and 3.2, respectively. The eventual numbers for 2023 were well above my prediction for the total number of named storms, though my forecasts for hurricanes and major hurricanes were actually slight overestimates. The (preliminary) Accumulated Cyclone Energy value for the 2023 season is 146, solidly above average. This measure of activity accounts both for strength and duration of tropical cyclones. The exact value sometimes shifts when post-season analysis is complete. Overall, the 2023 season was a mixed bag, well above average in some indicators and near to slightly below in some others. This reflected the unusual conditions that made predicting 2023's outcome particularly tricky.

The 2023 season took place during a fairly strong El Niño event, meaning that equatorial Pacific sea surface temperatures were well above recent normals (the anomalies in different regions are shown in the diagram above). There's a well-established correlation between these anomalies and weather trends throughout the rest of the world, including stronger shear over the Atlantic ocean and a weaker Bermuda high. These tend to led to suppressed hurricane activity and more storms curving out to sea, respectively.

Though several cyclones this season struggled with wind shear, the overall wind shear pattern was not the typical one for an El Niño (see the figure above). Indeed, most of the main development region of the Atlantic basin had below-normal zonal wind shear, where zonal means the component of wind shear in the longitudinal direction. The following diagram illustrates just how unusual this combination of low wind shear and El Niño is, relative to the historical record.

The primary reason that El Niño did not behave normally was the incredibly warm sea surface temperatures in the tropical Atlantic. These warm waters were the result of a combination of anthropogenic global warming and a spring of very weak trade winds, which left the surface portion of the ocean unmixed with cooler waters below. This helps to explain the large number of named storms that formed in 2023. Fortunately for many land areas, however, the other common effect of El Niño did manifest: the Atlantic subtropical ridge was extremely weak all season, allowing many storms to recurve out to sea without affecting land. This included the season's strongest storm, category 5 Hurricane Lee. In fact, 2023 had the lowest death toll and damages from tropical cyclones dating back at least to the 2015 season.

2023's activity also came in intense bursts. The month of June was quite active with three named storms, including two tropical storm formations (Bret and Cindy) in the tropical Atlantic, which is the first such occurrence on record. After that, only one storm formed between June 26 and August 19! The floodgates opened after that, however, with the period from August 20 and September 28 seeing the formation of a whopping 13 named storms (a new record, beating 2020), and 5 hurricanes (tying a record last set in 2012). November, the last month of hurricane season, saw no formations at all.

In my region-by-region predictions, I forecasted that the Caribbean islands would be at high risk this season, and that the coast of the Gulf of Mexico and U.S. east coast would be at relatively low risk. These predictions were reasonably accurate, since the majority of tropical cyclones which affected land this year did so in the Lesser Antilles. Of course, Hurricane Idalia's category 3 landfall in the big bend region of Florida was the one major exception. Idalia caused significant impacts, but they were smaller in magnitude compared to other major hurricane impacts in the region in previous years due to the landfall location and the relatively small radius of maximum winds. Some other notable facts or records from 2023 include:

• Though it wasn't operationally identified at the time, a unnamed subtropical cyclone formed in the northwestern Atlantic on January 16, and became the strongest tropical or subtropical Atlantic cyclone ever recorded in January
• Hurricane Franklin's minimum pressure of 926 mb was the lowest ever recorded in a tropical cyclone that far north in the open Atlantic
• Tropical Storm Philippe claimed the unusual record of longest-lasting Atlantic tropical cyclone with a peak intensity of under 70 mph

The 2023 season was unpredictable from start to finish, but ultimately had relatively mild impacts compared to many other recent years.

Sources: https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf, https://yaleclimateconnections.org/2023/11/the-unusual-2023-atlantic-hurricane-season-ends/, https://tropical.colostate.edu/Forecast/2023-11.pdf

Professor Quibb's Picks – 2023

My personal prediction for the 2023 North Atlantic Hurricane season (written May 27, 2023) is as follows:

15 cyclones attaining tropical depression status,
14 cyclones attaining tropical storm status,
8 cyclones attaining hurricane status,
4 cyclones attaining major hurricane status.

This prediction is near the 1991-2020 averages of 14.4 tropical storms, 7.2 hurricanes, and 3.2 major hurricanes each season in the Atlantic basin. I expect that 2023 will thus be an about average season. Below, I'll discuss the various factors involved in making this prediction. Note that the the NOAA identified a unnamed subtropical storm that formed in January 2023 in the western subtropical Atlantic, which was not designated operationally at the time. This storm is included in the above total, and will be covered on this blog once a tropical cyclone report on it is released.

I'll begin as usual with the El Niño Southern Oscillation (ENSO) index. Though simply a measure of sea surface temperature anomalies in the equitorial Pacific Ocean, it is correlated with trends in tropical cyclone activity all around the globe. For the Atlantic specifically, warmer than normal Pacific waters (El Niño) tend to give quieter Atlantic seasons, while cooler than normal waters (La Niña) lead to busier Atlantic seasons. It's worth noting that our understanding of this phenomenon, as well as possibly the ENSO cycle itself, has changed over the last few decades.

Indeed, even as oceans have drastically warmed overall over the past 40 years due to anthropogenic climate change, the equatorial Pacific has actually slightly cooled; relative to average, La Niña events have been much more frequent and intense recently than El Niño ones (read more here). For instance, La Niña conditions dominated for almost three years from 2020-2023. It's not certain exactly how or why this is occurring. Nevertheless, in 2023 specifically, things are changing.

A rapid warming is underway in the Pacific, and it's widely expected that an El Niño will begin soon, becoming moderate to strong by the latter half of hurricane season. This should have a significant suppressing effect on Atlantic tropical cyclone activity come summer.

Nevertheless, there are some signs that point in the opposite direction.

Moving from the Pacific to the Atlantic, we also see above average sea surface temperatures in the main cyclone formation regions, including the tropical Atlantic, the Caribbean, and the Gulf of Mexico. The effect of these anomalies on hurricane formation is more straightforward: warmer oceans mean more favorable conditions for development and intensification. It's worth noting that some of the warmest areas are in the tropics rather than the subtropics this year, where they will likely give a greater boost to tropical cyclones. The best recent historical analog for this sea surface temperature profile in May is 2010, a very active hurricane season.

One last major factor to examine is wind shear. The figure below, from Colorado State University's annual hurricane forecast report, shows different possible atmospheric wind profiles and how they might influence Atlantic hurricane activity.

The graphic above shows two possible scenarios for wind shear across the MDR (Main Development Region) of the Atlantic. The vertical direction indicates height in the atmosphere, and the horizontal axis is the component of the wind speed in the west-east direction (left is west, right is east) averaged across the indicated area. At lower altitudes, the east-to-west trade winds dominate the scene, but the wind direction may often change several miles aloft. The change of west-east wind speed with height is known as zonal wind shear and has significant implications for cyclone activity. In the unfavorable (blue) profile, the surface trade winds are stronger but the winds switch east near the top of the troposphere, the layer of Earth's atmosphere where most weather occurs. This makes it difficult for vertically aligned vortices to form, because different levels of a nascent circulation are pushed in opposite directions.

The red profile, in contrast, is a relatively uniform westerly wind at every level, meaning wind shear is low and conditions are favorable for tropical cyclone development. CSU takes spring zonal wind shear measurements into account when making their forecast; this shear has been a bit lower than normal for 2023 so far. Of course, this could change: El Niño also sometimes brings about a high zonal shear regime across the Atlantic. Putting all this together, I'm forecasting a near average hurricane season. I'll give a finer analysis of the risks by region. My estimates are on a scale from 1 (least risk) to 5 (most risk).

U.S. East Coast: 2
I'll put the east coast at lower than usual risk this year. The subtropical Atlantic has consistently been dominated by troughs this year so far, so cyclones reaching the latitude of the east coast have a good chance of recurving to the east. The oncoming El Niño may bring an early fall to the continental U.S., shutting down development in this region by October.

Yucatan Peninsula and Central America: 3
A more active Pacific hurricane season could help suppress cyclone formation on the other side of central America this summer. However, Atlantic waters are particularly warm in the southwestern Caribbean, which is always a danger zone for rapid intensification. I expect most of the season to be quiet in this region, but the possibility of a few strong storms brings the risk up to a 3.

Carribean Islands: 4
El Niño aside, the tropical Atlantic looks as favorable as it has looked in a while: temperatures are very warm, and the Saharan air layer is less prominent than usual near Africa. Look for possible long-track hurricanes forming and affecting the Caribbean islands, before likely turning northward. I'll put the eastern islands at greater risk than the western ones.

Gulf of Mexico: 2
The same factors at play for the U.S. East Coast give a similar story here. Though waters are warm, I think shear and atmospheric steering currents should shield the Gulf coast from the worst impacts, particularly during the latter half of the season. July and August may be the riskiest months for a Gulf hurricane landfall if one does occur.

Overall, I expect the 2023 Atlantic hurricane season to be around average, with perhaps a slightly larger number of hurricanes and major hurricanes than usual (though I expect most of these to go out to sea). Nevertheless, this is just an amateur forecast. Individuals in hurricane-prone areas should always have emergency measures in place. For more on hurricane safety sources, see here. Remember, devastating storms can occur even in otherwise quiet seasons.

Sources: https://yaleclimateconnections.org/2023/04/a-mystery-in-the-pacific-is-complicating-climate-projections/, https://www.nhc.noaa.gov/sst/rsst_atl_anom_loop.php, https://tropical.colostate.edu/forecasting.html

Hurricane Names List – 2023

The name list for tropical cyclones forming in the North Atlantic basin for the year 2023 is as follows:

Arlene
Bret
Cindy
Don
Emily
Franklin
Gert
Harold
Idalia
Jose
Katia
Lee
Margot
Nigel
Ophelia
Philippe
Rina
Sean
Tammy
Vince
Whitney

This list is the same as that for the 2017 season, with the exception of Harold, Idalia, Margot, and Nigel, which replaced the retired names Harvey, Irma, Maria, and Nate, respectively.

2022 Season Summary

The 2022 Atlantic hurricane season was close to average in overall activity, with a total of

16 cyclones attaining tropical depression status,
14 cyclones attaining tropical storm status,
8 cyclones attaining hurricane status, and
2 cyclones attaining major hurricane status.

Before the beginning of the season, I predicted that there would be

20 cyclones attaining tropical depression status,
19 cyclones attaining tropical storm status,
9 cyclones attaining hurricane status, and
5 cyclones attaining major hurricane status.

The average numbers of tropical storms, hurricanes and major hurricanes (over the 30 year period 1991-2020) were 14.4, 7.2, and 3.2, respectively. The eventual numbers for 2022 were quite close to this average, though with realtively few major hurricanes. The (preliminary) Accumulated Cyclone Energy value for the 2022 season was 95, a little below average but well-within "near normal" range. This measure of activity accounts both for strength and duration of tropical cyclones. The exact value sometimes shifts when post-season analysis is complete. This year, my predictions were significantly above the outcome, except in the hurricanes category where it was fairly close. Other official forecasts, such as those by the NOAA and by Colorado State University, were similarly above the mark. So what happened?

As predicted before the season, La Niña conditions prevailed throughout the summer and fall. This meant that equatorial Pacific sea surface temperatures were below normal, as the above diagram indicates for different zones. Such a strong La Niña would usually correlate to increased Atlantic activity, and was a major factor in pre-season forecasts. Atlantic ocean temperatures in hurricane formation zones also ran above normal, so we'll have to look elsewhere for an explanation of the underperformance.

Of particular note is the fact that no tropical cyclones formed during the month of August. This was the first time this had occurred since 1997, and the first time ever that this was observed to happen during a La Niña, dating back to the mid-20th century when detailed observations of the El Niño cycle began. Further, the only storms which formed prior to August were three short-lived tropical storms. The first hurricane was Danielle, which reached hurricane status on September 3, becoming the latest first hurricane in the Atlantic since 2013. In contrast, September through November was an unusually busy period, more consistent with climatological patterns.

The main culprits for the August quiet period were elevated wind shear and dry air. The map above charts the cumulative anomalies in relative humidity in the mid-levels of the atmosphere over the period August 1-22, 2022, vs. 30-year averages. The main development region in the tropical Atlantic east of the Caribbean was the epicenter of a dry air spell which lasted most of the month. Saharan dust was a major contributor to the dry air event. It prevented tropical waves from developing convective activity, which in turn would allow them to build vorticity, gain latitude, and detach from the Intertropical Convergence Zone (ITCZ). When tropical waves reached the Caribbean, another obstacle awaited them.

The first three weeks of August also saw well above average wind shear in the Caribbean sea. Wind shear measures the difference in winds at different heights in the atmosphere; a greater difference in winds prevents atmospheric vortices from the low and mid-levels aligning vertically, or "stacking". This is a necessary ingredient for tropical cyclones to form and strengthen. In comparison to my pre-season prediction, this wind shear event was especially surprising, since I had cited models which indicated wind shear would be below average for the June-July-August period. It's not clear why the model forecast was poor, but the immediate sources of the shear were systems called tropical upper-trospheric troughs (TUTTs). These are large areas of low pressure in the higher levels of the atmosphere, in this case usually located over the central Atlantic northeast of the Caribbean. These features generate counterclockwise flow, which runs opposite to the low-level east-to-west trade winds in the tropics. This combination amounts to high wind shear.

In my region-by-region predictions, I put all sectors of the Atlantic basin at higher-than-normal risk, but had only the Gulf of Mexico at highest risk. Unfortunately, this part of the forecast verified. The strongest winds and largest impacts of 2022 came from Hurricane Ian, which made landfall along the Florida Gulf coast as a top-end category 4 hurricane. Elswhere, Hurricane Fiona was the most impactful; it primarily affected Purto Rico and neighoring islands, as well as Atlantic Canada.

Some other notable facts or records from 2022 include:

• The 2022 season ended a streak of six consecutive seasons in which a tropical cyclone had formed prior to June 1
• Tropical Storm Bonnie and Hurricane Julia both crossed from the Atlantic to the Pacific basins and retained their names; this was the first time this had happened twice on record
• When Fiona made landfall as an extratropical cyclone in Nova Scotia, it broke the record for lowest barometric pressure ever reported in Canada; the new record was 931.6 mb
• Martin and Nicole were hurricanes simultaneously, which was the third time this had occurred in November, after 1932 and 2001
• Nicole was the first Florida hurricane landfall in November since Hurricane Kate in 1985

The headline numbers for 2022 tell the story of an average season, but hide several surprising twists. This year is a good reminder that long-term hurricane season forecasts have a long way to go!

Sources: https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf, https://yaleclimateconnections.org/2022/08/quiet-in-the-atlantic-will-we-go-0-for-august/

Professor Quibb's Picks – 2022

My personal prediction for the 2022 North Atlantic Hurricane season (written May 17, 2022) is as follows:

20 cyclones attaining tropical depression status,
19 cyclones attaining tropical storm status,
9 cyclones attaining hurricane status,
5 cyclones attaining major hurricane status.

This prediction is well above the 1991-2020 averages of 14.4 tropical storms, 7.2 hurricanes, and 3.2 major hurricanes each season in the Atlantic basin. I expect that 2022 will thus be the third consecutive season with significantly above-average activity. Below, I'll discuss the various factors involved in making this prediction.

The first factor to consider is, as always, the El Niño Southern Oscillation (ENSO) index, which is a numerical measure of sea surface temperature anomalies in the equitorial Pacific ocean. When these waters are warmer than normal (El Niño), Pacific tropical cyclone activity is elevated and Atlantic activity is suppressed. When they are cooler (La Niña), the reverse is true. Remarkably, La Niña conditions are expected to persist through the summer, making 2022 the third consecutive La Niña year! The graphic below shows various model predictions for the ENSO index through the rest of the year. The official threshold for a La Niña event is -0.5, and the index is expected to linger near or below this threshold by a majority of models.

Once again, it seems likely that La Niña will give this year's activity a significant boost.

The map below shows current sea surface temperature anomalies in the Atlantic. They are mostly above average, though no region in particular stands out too much. Note that sea surface temperature anomalies are generally measured relative to a mean based on the last few decades. Therefore, this does not account for anthropogenic ocean warming; measured against pre-industrial levels, these anomalies would be greater.

Until May, the main developement region (between the western African coast and the Caribbean) actually had somewhat below average sea surface temperatures. Recently, however, the east-to-west trade winds have relaxed. When trade winds are strong, they churn up cooler ocean waters from below the surface; they also directly inhibit cyclone formation by making it hard for vortices to form (see here for more). Therefore, recent trends are concerning, as the eastern Atlantic has warmed significantly in the last month. If this continues, long-track hurricanes are likely by the heart of the season. Finally, we'll take a look at the following prediction for wind shear anomalies in the first half of hurricane season (June-July-August).

Blue indicates below-average wind shear and hence more favorable conditions for hurricanes to form. The signal in this model is quite strong; it seems likely that the Caribbean in particular will have little wind shear during early hurricane season. Note that below-average shear is consistent with a La Niña pattern, but this doesn't occur everywhere: in the deep tropics near Africa, there's an area of above-average shear. In this model, the region of above-average shear even drifts northward as the summer progresses. Nevertheless, almost all factors point to a quite active hurricane season.

Using these and a few other factors, I'll give a finer analysis of the risks by region. My estimates are on a scale from 1 (least risk) to 5 (most risk).

U.S. East Coast: 4
Most areas are at above-average risk this year, and the east coast is no exception. The good news is that I expect most of the cyclones forming in the main development region during August and September will curve out to sea, since the shear pattern favors the consolidation of tropical waves more at their northern ends. Storms forming closer to home will be the ones to watch for.

Yucatan Peninsula and Central America: 4
The monsoon in this region is currently quite active. This elevates the risk for some messy tropical storms near central America in late May and June, with flooding and mudslides the main concern. It's difficult to say this early, but October and November may also be an active time for the western Caribbean.

Caribbean Islands: 4
All the general factors discussed above also suggest the Caribbean will be at elevated risk, but I don't see anything specific pointing to tracks through the islands. I do expect an early start to activity in the region, with multiple storms by the time August comes around.

Gulf of Mexico: 5
The Gulf coast has experienced an exceptional number of hurricane landfalls already during the 2020 and 2021 seasons. With the La Niña continuing, this is unlikely to abate this year, unfortunately. The atmospheric setup on models this year also seems to favor steering cyclones into the Gulf, should they form in the Caribbean. This merits a maximum risk designation.

Overall, I expect the 2022 Atlantic hurricane season to be well above average. Nevertheless, this is just an amateur forecast. Individuals in hurricane-prone areas should always have emergency measures in place. For more on hurricane safety sources, see here. Remember, devastating storms can occur even in otherwise quiet seasons.

Sources: https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf, https://www.tropicaltidbits.com, https://www.trackthetropics.com/saharan-air-layer-sal-tracking/, https://www.nhc.noaa.gov/sst/

Hurricane Names List – 2022

The name list for tropical cyclones forming in the North Atlantic basin for the year 2022 is as follows:

Alex
Bonnie
Colin
Danielle
Earl
Fiona
Gaston
Hermine
Ian
Julia
Karl
Lisa
Martin
Nicole
Owen
Paula
Richard
Shary
Tobias
Virginie
Walter

This list is the same as that for the 2016 season, with the exception of Martin and Owen, which replaced the retired names Matthew and Otto, respectively.

2021 Season Summary

The 2021 Atlantic hurricane season was quite active, with a total of

21 cyclones attaining tropical depression status,
21 cyclones attaining tropical storm status,
7 cyclones attaining hurricane status, and
4 cyclones attaining major hurricane status.

Before the beginning of the season, I predicted that there would be

17 cyclones attaining tropical depression status,
16 cyclones attaining tropical storm status,
8 cyclones attaining hurricane status,
5 cyclones attaining major hurricane status.

The average numbers of tropical storms, hurricanes and major hurricanes (over the 30 year period 1991-2020) were 14.4, 7.2, and 3.2, respectively. This puts the 2021 season a bit above average overall, with a much higher than usual number of named storms but near average numbers of hurricanes and major hurricanes. Likewise, my predictions underestimated the number of named storms, but were close on hurricanes and major hurricanes. The 21 named storms were the third-most recorded for an Atlantic season at the time, behind 2020 and 2005. The Accumulated Cyclone Energy (ACE) value for the 2021 season (which accounts for duration and intensity of storms as well as number) was roughly 145, once again above normal but not by a huge margin. The exact figure will likely shift slightly in post-season analysis.

A bevy of short-lived, weak systems inflated the total number for the season, especially early on. There were three named storms in June for the first time since 1968. Hurricane Elsa set a record for earliest fifth named storm when it was named on July 1. However, the end of the season was surprisingly quiet. With the exception of meandering Tropical Storm Wanda, which spent a week in early November moving around the north Atlantic, there was no activity from October 4 onward. This is quite unusual: on average, one would expect around 3 named storms and at least 1 hurricane during that time. Even stranger, the entire world experienced a lack of strong cyclones during October and November 2021. To explain this behavior, we'll examine a few factors.

At the beginning of the season, an ongoing La Niña event was on the wane, and indeed it officially ended over the summer. However, equatorial Pacific sea temperature anomalies remained negative (consistent with La Niña) and even began to decrease again by late in the year. The relevant regions of the Pacific and their temperature anomalies throughout the year are illustrated above. Overall, the weak La Niña that occurred was consistent with pre-season predictions. It is correlated with lower wind shear in the Atlantic and thus consistent with the somewhat above normal activity observed. Likewise, the tropical north Atlantic had fairly warm ocean temperatures, which helped tropical cyclones to form and intensify. However, this doesn't explain why the Atlantic shut down in October.

2021 featured a particularly strong west African monsoon; note the high precipitation over Africa around 10° N or so between June and August in the map above. This is signficant because tropical waves, the precursors to most Atlantic tropical cyclones, form over Africa and move westward into the Atlantic. Indeed, in contrast to 2020, a larger proportion of storms originated in the tropical Atlantic (see the map of storm tracks below):

Every year, the opportunity for cyclone formation off of Africa closes in early October, when the wave axis shifts toward the equator and east Atlantic temperatures start to get cooler. The center of activity usually then shifts to the Caribbean, but the Caribbean saw an unusual amount of dry sinking air late in the year, stifling any formation. This is again in stark contrast to 2020, when the west Caribbean saw its most active period in recorded history from October through November. These factors help to indicate why the 2021 season ended earlier than expected.

In my predictions, I put the Caribbean islands and the Gulf of Mexico at highest risk, with the U.S. east coast and central America at lower risk. These predictions were fairly good: Hurricane Elsa, Tropical Storm Fred, Hurricane Grace, and Hurricane Ida impacted the Caribbean Islands, while Ida and Hurricane Nicholas had the greatest Gulf impacts (though Grace also hit the Yucatan and the southwest Gulf). The Caribbean impacts might have been greater still had some of the above storms not tracked directly over the greater Antilles. No landfalls occurred in central America and only the extremely unusual Henri had any significant impact on the U.S. east coast as a tropical cyclone.

Some other notable facts or records from 2021 include:

• Tropical Storm Ana's formation on May 22 made 2021 the seventh consecutive season with a named storm before June 1
• Elsa was the easternmost forming early July hurricane in the tropics since 1933; it also had the highest forward speed of any known Atlantic hurricane in the tropics
• Grace's remnants reformed as a tropical storm in the eastern Pacific and were named Marty
• Henri was the slowest-moving cyclone ever recorded in the U.S. northeast; this led to unusual flooding impacts in the region
• Ida tied 2020's Hurricane Laura for highest winds of a landfalling Louisiana hurricane (150 mph)

Finally, Hurricane Sam was the season's strongest storm, with winds of 155 mph and a central pressure of 929 mb. It was a long-lived and powerful storm, clocking in at over 50 ACE just on its own and holding major hurricane status for 7.75 consecutive days. Despite this, it went out to sea and didn't significantly impact any landmasses.

The 2021 season was quite active, though with many weak systems. The vast majority of the season's damage and loss of life were due to Hurricane Ida, which made landfall in Louisiana as a category 4 hurricane.

Sources: https://www.washingtonpost.com/weather/2021/11/22/earth-hurricane-activity-record-quiet/, https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf

Professor Quibb's Picks – 2021

My personal prediction for the 2021 North Atlantic Hurricane season (written May 16, 2021) is as follows:

17 cyclones attaining tropical depression status,
16 cyclones attaining tropical storm status,
8 cyclones attaining hurricane status,
5 cyclones attaining major hurricane status.

I predict that the 2021 season will feature above-average activity, though not at the pace of the record-breaking 2020 season. Every decade, the NOAA revises the 30-year averages for number of cyclones to reflect new data and better track climate change; the 1991-2020 averages were 14.4 tropical storms, 7.2 hurricanes, and 3.2 major hurricanes, up from 12.1 tropical storms, 6.4 hurricanes, and 2.7 major hurricanes in the 1981-2010 period. My forecast therefore exceeds this new average, but not by a great deal.

In making this prediction, I first consider the El Niño Southern Oscillation (ENSO) index, which measures sea surface temperature anomalies in the equitorial Pacific ocean. Warmer than normal temperatures (El Niño) correlate to decreased Atlantic activity (and increased Pacific activity) and cooler than normal temperatures (La Niña) the opposite. A La Niña event, the strongest in nearly a decade, is currently ongoing and began in the latter half of 2020, contributing to the frenzy of activity of that season.

Nevertheless, recent data indicate that the La Niña is waning and models generally show this should continue into the summer (see the above graph - the vertical axis indicates the relevant temperature anomaly). However, the ensemble average still indicates ENSO neutral to negative conditions. Overall, I predict lingering La Niña effects will still boost activity this year.

In the same vein, most of the 21st century has been in the positive phase of the theorized Atlantic Multidecadal Oscillation, which has led to elevated sea surface temperatures, and, generally, more hurricanes. It's hard to disentangle such long-term climate cycles from modern anthropogenic global warming, and the headline regarding ocean temperatures is largely the same as the last few years: the Atlantic, Caribbean, and Gulf of Mexico will be warm, even by recent standards. The largest anomalies are likely once again to be in the subtropical Atlantic.

A few other factors that influence tropical cyclone formation are relative humidity of the atmosphere and wind shear. A moist atmosphere allows nascent tropical disturbances to develop thunderstorm activity and grow. Wind shear refers to a change in wind direction and speed between the lower levels and upper levels of the atmosphere; higher values of wind shear hamper tropical cyclones because they prevent them from becoming or remaining vertically stacked. Long-term models can give at least some sense of what average conditions to expect during peak hurricane season (see above: the top figure shows expected precipitation anomalies for August-October 2021 and the bottom zonal wind shear anomalies for the same period). Using these and a few other factors, I'll give a finer analysis of the risks by region. My estimates are on a scale from 1 (least risk) to 5 (most risk).

U.S. East Coast: 3
A mixed bag of conditions leaves the U.S. east coast with middling risk. Indications are that the summer will be wet in this region, with ample heat and moisture for tropical cyclones to form and strengthen. On the other hand, the Bermuda high looks a bit weaker than usual given the neutral to negative ENSO index, suggesting that hurricane tracks might veer east out to sea. With neutral ENSO more likely late in the year, expect fall fronts to reduce east coast risk by the end of September; if there are landfalls here, it will be in the front end of the season.

Yucatan Peninsula and Central America: 2
After a devastating 2020, these areas will (hopefully) experience much less hurricane activity this year. Preciptation forecasts (see above) anticipate a drier west Caribbean, and while wind shear will be lower than average in most of the basin, the same is not true for the eastern Caribbean, where threats to the Yucatan and Central America could form. If hurricanes do affect this region, I'd expect it to be in October and November; rapid intensification episodes close to land are the primary risk.

Caribbean Islands: 5
Even in the most active season in history last year, tropical cyclone activity in the main development region in the tropics between the Windwards and Africa was lackluster. Things will probably be different this year. The dusty Saharan Air Layer (SAL), and its suffocating effect on east Atlantic tropical waves, looks to be less prominent than usual. Furthermore, shear is low, temperatures are warm, and precipitation anomalies are at least around neutral over the tropical Atlantic. This could open the door for some long-track hurricanes à la 2017. The biggest question mark is whether these will avoid land or not, but everywhere from the Lesser Antilles to the Bahamas should be on high alert.

Gulf of Mexico: 4
Though maybe a little dry, the Gulf may have the highest sea surface temperature anomalies outside the subtropical Atlantic this summer. Storms forming near the Bahamas and homegrown hurricanes in the Gulf are both likely to occur at sometime in the year, putting this region at above-average risk.

Overall, I expect the 2021 Atlantic hurricane season to be above-average, though not exceptionally so. Nevertheless, this is just an amateur forecast. Individuals in hurricane-prone areas should always have emergency measures in place. For more on hurricane safety sources, see here. Remember, devastating storms can occur even in otherwise quiet seasons.



Sources: https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf, https://www.tropicaltidbits.com, https://www.trackthetropics.com/saharan-air-layer-sal-tracking/, https://www.wunderground.com/hurricane/articles/wind-shear-explainerhttp://www.webberweather.com

Hurricane Names List – 2021

The name list for tropical cyclones forming in the North Atlantic basin for the year 2021 is as follows:

Ana
Bill
Claudette
Danny
Elsa
Fred
Grace
Henri
Ida
Julian
Kate
Larry
Mindy
Nicholas
Odette
Peter
Rose
Sam
Teresa
Victor
Wanda

This list is the same as the list for the 2015 season, with the exception of Elsa and Julian, which replaced Erika and Joaquin, respectively, after those names were retired.

Professor Quibb's Picks – 2020

My personal prediction for the 2020 North Atlantic hurricane season (written May 13, 2020) is as follows:

20 cyclones attaining tropical depression status,
18 cyclones attaining tropical storm status,
9 cyclones attaining hurricane status, and
5 cyclones attaining major hurricane status.

I predict that the 2020 Atlantic hurricane season will continue the active trend of the last few years and likely feature a well above-average number of cyclones, although uncertainty in my forecast is higher than average. Note that the average Atlantic hurricane season (1981-2010 average) has 12.1 tropical storms, 6.4 hurricanes, and 2.7 major hurricanes. The main factor in support of this claim is the potential for a neutral to negative El Niño Southern Oscillation (ENSO) index this summer and autumn. This index, a measure of equatorial sea temperature anomalies in the Pacific ocean, has an inverse correlation with Atlantic hurricane activity: negative indices (corresponding to a La Niña) tend to favor more active seasons.

Unlike the last two years, there is a great deal of spread in the model forecasts for this year's ENSO. Some models have the index remain positive, while others show a strong La Niña event developing by season's end. The dynamical models (whose average is represented by the thick red line) lean toward La Niña more than the statistical models (green), which favor using historical data for prediction over simply modeling future changes in weather. Due to a rapid plunge of Pacific equatorial sea surface temperature anomalies in the last few weeks, I'm putting more weight on the dynamical solution. This would suggest a very active season, especially since 2018 and 2019 were active despite neutral to slightly positive ENSO index conditions.

Meanwhile, Atlantic water temperatures are running uniformly warmer than average for this time of year, and this is expected to continue through the summer. No particular regions stand out though: the Gulf of Mexico, Caribbean, and subtropical Atlantic will all have moderately high anomalies, and the tropical Atlantic just a little bit less so. Expect tropical cyclone formation in many areas this year, and not quite as much emphasis on the subtropical Atlantic.

The above image shows the strength of the Saharan Air Layer (SAL) of the atmosphere as it appeared on May 12, 2020. Tropical trade winds carry dust particles and dry air from the Sahara desert over water throughout the year, but this has particular relevance to the development of tropical waves emerging off of the west African coastline: the more dry air and dust, the more thunderstorm activity in the region is suppressed. The SAL is quite strong as of now (though there is a typical decline throughout spring), so expect a late start for long-track hurricanes this year. Come September, however, other factors indicate high risk for Cape Verde hurricanes.

I'll discuss a few more smaller-scale factors in association with assigning risks to different parts of the Atlantic basin. My estimates are on a scale from 1 (least risk) to 5 (most risk):

U.S. East Coast: 4
The position of the Bermuda/Azores high pressure system correlates with the ENSO index and has a great influence on tropical cyclone tracks. I predict that this high will remain further east than typical La Niña events, increasing the risk to the east coast but lowering it for the Gulf of Mexico. The threat to the east coast will start early to the season, in July and August.

Yucatan Peninsula and Central America: 4
The western Caribbean is at higher risk for tropical cyclones than in any of the last 3 seasons, particularly when early fall rolls around. Some of the Atlantic's highest ocean temperatures will be in this region, and wind shear will be below normal. Expect some low-latitude cyclones, possibly affecting Nicaragua and Honduras.

Caribbean Islands: 4
The Caribbean, too, looks to be at greater-than-average risk this year. Once the tropical wave train gets going in earnest, look for long-track storms approaching from the east (primarily in September). The east Caribbean should be less of a hurricane graveyard than the last few seasons, so cyclones following tracks similar to Hurricane Matthew and approaching Hispaniola and Puerto Rico from the south are likelier than average.

Gulf of Mexico: 3
Waters in the Gulf are once again very warm, and some "home-grown" cyclone development is likely. Nevertheless, I forecast that the strongest cyclones will track elsewhere for most of the season. Come October, however, there is still a moderate chance for storms moving south to north from near the Yucatan Peninsula toward the United States gulf coast, similar to Hurricane Michael.

Overall, I expect the 2020 Atlantic hurricane season to feature well above-average activity. Nevertheless, this is just an amateur forecast. Individuals in hurricane-prone areas should always have emergency measures in place. For more on hurricane safety sources, see here. Remember, devastating storms can occur even in otherwise quiet seasons.

Sources: https://www.tropicaltidbits.com/analysis/models/, https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf, http://trackthetropics.com/saharan-air-layer-sal-tracking/

Hurricane Names List – 2020

The name list for tropical cyclones forming in the North Atlantic basin for the year 2020 is as follows:

Arthur
Bertha
Cristobal
Dolly
Edouard
Fay
Gonzalez
Hanna
Isaias
Josephine
Kyle
Laura
Marco
Nana
Omar
Paulette
Rene
Sally
Teddy
Vicky
Wilfred

This list is the same as the list for the 2014 season because no names were retired that year.

2019 Season Summary

The 2019 Atlantic hurricane season had above-average activity, with a total of

20 cyclones attaining tropical depression status,
18 cyclones attaining tropical storm status,
6 cyclones attaining hurricane status, and
3 cyclones attaining major hurricane status.

Before the beginning of the season, I predicted that there would be

15 cyclones attaining tropical depression status,
14 cyclones attaining tropical storm status,
6 cyclones attaining hurricane status, and
3 cyclones attaining major hurricane status.



The average number of named storms, hurricanes, and major hurricanes for an Atlantic hurricane season (over the 30-year period 1981-2010) are 12.1, 6.4, and 2.7, respectively. The 2019 season was much above average in the number of tropical storms (in fact, it was only the sixth year since the advent of the modern naming system that the "S" name was used), but near average in the hurricane and major hurricane categories. This stemmed in part from the fact that the season featured many short-lived, weak tropical storms and a few powerful hurricanes. The ACE value for the 2019 season (which accounts for duration and intensity of storms as well as number) was around 130, just above the average. Apart from the addition of a few extra short-lived cyclones, my predictions were on target.

The El Niño event initially forecast to continue (see the first image in this post) through the 2019 summer/fall died out by July, transitioning to an ENSO neutral/slightly positive state that continued through November. Since an El Niño event typically suppresses hurricane activity, this factor alone would suggest an average to slightly below average season. Indeed, 2019 did display some of the hallmarks of an El Niño season, including storm tracks curving away from the north American mainland and wind shear in the main development region (the Caribbean and tropical western Atlantic). However, the "tropical wave train" off of Africa was quite vigorous for most of the season, and even extended later than usual into October (with Tropical Depression Fifteen among the latest forming tropical waves off of Africa ever recorded). Also offsetting the residual El Niño was the continuing ocean warmth of the subtropical Atlantic, which contributed to prolific development; nearly half of the season's storms formed in the subtropical Atlantic.

The most damaging storms of the 2019 season were Hurricane Dorian and Tropical Storm Imelda. Dorian devastated the Bahamas, especially Abacos Island and Grand Bahama, as a category 5 hurricane. It was the strongest landfalling storm on record for the region and was tied for the most intense landfalling hurricane by windspeed ever recorded in the Atlantic (with the Labor Day hurricane of 1935). Imelda was only a tropical storm, but its slow motion over southeast Texas caused a major flooding event similar to, though slightly less severe than, those associated with Harvey and Florence in the previous two years. Some other notable facts and records from the 2019 season include:

• Seven of the eighteen named storms of the 2019 season lasted less than 24 hours, a new record
• Subtropical Storm Andrea formed on May 20, marking the fifth consecutive year in which a named storm developed before the official start of the season on June 1 (also a new record)
• Dorian was the strongest Atlantic hurricane ever recorded so far north at its latitude of peak intensity, 26.6° N
• When Lorenzo became a category 5 hurricane, it marked only the seventh time on record that multiple category 5 hurricanes were recorded in a season; Lorenzo was the easternmost forming category 5 on record
• Pablo strengthened into a hurricane farther north and east than any cyclone previously observed, at 42.8° N, 18.3° W, only a few hundred miles west of the coast of Spain

Overall, the 2019 season was somewhat above average (though near average in number of hurricanes and major hurricanes), with Hurricane Dorian the strongest and most damaging.

Professor Quibb's Picks – 2019

My personal prediction for the 2019 North Atlantic hurricane season (written May 19, 2019) is as follows:

15 cyclones attaining tropical depression status,
14 cyclones attaining tropical storm status,
6 cyclones attaining hurricane status, and
3 cyclones attaining major hurricane status.

Following a fairly average hurricane season in 2018 (which nevertheless featured two devastating major hurricanes), I predict that the 2019 season will see a comparable number of cyclones, albeit with rather different areas to watch. Note that the average Atlantic hurricane season (1981-2010 average) has 12.1 tropical storms, 6.4 hurricanes, and 2.7 major hurricanes. As with any season, our prediction begins with a look at the El Niño Southern Oscillation (ENSO) index, a measure of equatorial sea temperature anomalies in the Pacific ocean that have a well-documented impact on Atlantic hurricane activity. These anomalies are currently positive, corresponding to an El Niño state, and have been since last fall. The image below (click to enlarge) shows model predictions for the ENSO index through the remainder of 2019.

In comparison to the last several years, the situation is more static: no significant change of state is expected during this year's hurricane season (though there is, of course, significant uncertainty). This state of affairs tends to suppress hurricane activity and increase the chance of cyclones in the subtropical Atlantic curving away from the North American coastline (unlike, for example, the unusual track of Hurricane Florence last year).

This is fortunate, because all indications are the subtropical Atlantic will continue to churn out named storms as it did last season. Sea surface temperatures continue to run high in the region, and El Niño effects are not as pronounced there, partially explaining why my prediction still features an above average number of storms. Other factors also somewhat offset the El Niño: ocean temperatures in the tropical Atlantic (the birthplace of most long-track hurricanes) are slightly above normal this year, a trend expected to persist over the next several months. The atmosphere has also been less dry in the region, with less Saharan dry air than in 2018 and the beginning of the 2017 season to quash developing tropical waves. Expect the tropics to be less hostile to long-track hurricane formation than last year, when all cyclones taking the southerly route dissipated upon entering the Caribbean.

My estimated risks on a scale from 1 (least risk) to 5 (most risk) for different specific parts of the Atlantic are as follows:

U.S. East Coast: 3
Though the subtropical Atlantic will be active, I predict less of a risk to the U.S. coastline, with a smaller chance of a Florence-like system this year. Though there may be a few hurricanes passing offshore, most should recurve out over open water. Bermuda, however, is at higher risk.

Yucatan Peninsula and Central America: 2
These regions may benefit the most from a persistent El Niño, with wind shear making the development of an intense hurricane in the western Caribbean difficult. Further, I expect tracks to curve northward more often than striking Central America directly. Later season cyclones originating in the monsoonal gyre near Panama may pose the primary threat, and these tend to be principally rainmakers.

Caribbean Islands: 4
With the main development region (MDR) of the tropical Atlantic more favorable this year, the Caribbean is unlikely to continue the reprieve last year that followed arguably its worst season of all time (2017). Early season storms are still likely to fizzle out due to El Niño-related shear, but a wetter atmosphere suggests that tropical disturbances will have to be watched carefully. This includes a greater possibility of tropical cyclogensis in the Caribbean itself.

Gulf of Mexico: 3
Sea temperatures are consistently higher in the Gulf this year than they have been recently, especially near the Florida gulf coastline, but conditions here overall are a mixed bag. A strong jet stream across the continental U.S. will support more severe thunderstorms over land this summer, but this actually may work against cyclones thriving in the region. Balancing these factors yields an average risk, though this overall rating is a combination of a higher-than-normal risk in the eastern Gulf and a lower-than-normal risk farther west.

Overall, I expect the 2019 hurricane season to feature close-to-average activity. Nevertheless, this is just an informal forecast. Individuals in hurricane-prone areas should always have emergency measures in place. For more on hurricane safety sources, see here. Remember, devastating storms can occur even in otherwise quiet seasons.

Sources: https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf, https://www.cpc.ncep.noaa.gov/products/CFSv2/CFSv2seasonal.shtml, https://www.ospo.noaa.gov/Products/ocean/sst/anomaly/

Hurricane Names List – 2019

The name list for tropical cyclones forming in the North Atlantic basin for the year 2019 is as follows:

Andrea (used)
Barry (used)
Chantal (used)
Dorian (used)
Erin (used)
Fernand (used)
Gabrielle (used)
Humberto (used)
Imelda (used)
Jerry (used)
Karen (used)
Lorenzo (used)
Melissa (used)
Nestor (used)
Olga (used)
Pablo (used)
Rebekah (used)
Sebastien (used)
Tanya
Van
Wendy

This list is the same as the list for the 2013 season, with the exception of Imelda, which replaced the retired name Ingrid.

2018 Season Summary

The 2018 Atlantic Hurricane Season had above-average activity, with a total of

16 cyclones attaining tropical depression status,
15 cyclones attaining tropical storm status,
8 cyclones attaining hurricane status, and
2 cyclones attaining major hurricane status.

Before the beginning of the season, I predicted that there would be

18 cyclones attaining tropical depression status,
16 cyclones attaining tropical storm status,
8 cyclones attaining hurricane status, and
4 cyclones attaining major hurricane status.

The average number of named storms, hurricanes, and major hurricanes for an Atlantic hurricane season (over the 30-year period 1981-2010) are 12.1, 6.4, and 2.7, respectively. The 2018 season was somewhat above average in these categories, with the exception of the number of major hurricanes. The formation of many short-lived subtropical storms inflated the named storm total, but the Accumulated Cyclone Energy (ACE) value of 127 for the season was still above average. This value accounts for the duration and intensity of tropical cyclones as well as their number.

As usual, the ENSO oscillation was a major player in tropical cyclone activity this year. As hurricane season progressed into autumn, ocean temperatures of the equatorial Pacific trended higher than normal, signaling the advent of an El Niño event. Typically, such an event causes higher wind shear over the Atlantic and suppresses tropical cyclone activity, but it arose later in the year than anticipated, mitigating its effects.

The increase in wind shear during El Niño is most pronounced in the Caribbean Sea. Indeed, this region was a "graveyard" for tropical cyclones during 2018, as indicated by the above map of all the season's tracks. Every storm that entered the eastern Caribbean dissipated shortly thereafter due to unfavorable atmospheric winds. Ocean temperatures in the tropical Atlantic east of the Caribbean were also fairly cool for much of the season. This setup prevented long-track hurricanes from forming, with one notable exception: Hurricane Florence. Florence took a highly unusual route farther north but still pushed westward into the U.S. east coast. Overall, my predictions were slightly higher than the actual season activity, but they did correctly indicate the risk to the east coast.

The two most notable storms of the season were Hurricane Florence and Hurricane Michael. Florence made landfall in North Carolina, where it stalled and brought over 30 inches of rain to some areas. The record-breaking rainfall caused unprecedented flooding and extensive damage. Michael brought torrential rain to central America as it was forming and then went on to strengthen right up until landfall in the Florida Panhandle. With a pressure of 919 mb at landfall, Michael was at the time the 3rd most intense cyclone ever to make landfall in the United States and only the 4th category 5 hurricane ever recorded to do so. Some other notable facts and records from the 2018 Atlantic season include:

• The 2018 season had seven storms that were at some point subtropical, a new record
• On September 12, Florence, Helene, Isaac, and Joyce all coexisted in the Atlantic. This was the first time four named storms existed simultaneously since 2008
• Hurricane Leslie took a highly unusual track over the far eastern Atlantic near the end of its lifetime. As a result, the first tropical storm warning on record was issued for Madeira Island southwest of Portugal; Leslie became post-tropical just before landfalling in Portugal itself

Overall, the 2018 season was only a little above average but nevertheless featured two devastating major hurricanes.

Sources: https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf,

Professor Quibb's Picks – 2018

My personal prediction for the 2018 North Atlantic hurricane season (written May 16, 2018) is as follows:

18 cyclones attaining tropical depression status,
16 cyclones attaining tropical storm status,
8 cyclones attaining hurricane status, and
4 cyclones attaining major hurricane status.

In the wake of the especially devastating 2017 season, it is difficult to predict with any certainty the outcomes for this year. Once again, models indicate that the El Niño Southern Oscillation Index (or ENSO index) will be near zero or slightly positive during this hurricane season. This index, which is a certain quantitative measure of sea surface temperature anomalies in the tropical Pacific Ocean, has some ability to predict Atlantic hurricane activity. A positive index indicates an El Niño event, which tends to correlate with higher wind shear across the Atlantic basin and less tropical cyclone development. This effect is especially pronounced in the Gulf of Mexico and Caribbean Sea. The image below shows the ENSO forecast for this season (image from the International Research Institute for Climate and Society):

However, last year's forecast was qualitatively similar, but the index ended up dipping back negative and leaving very favorable conditions for hurricane formation. Though consideration of the ENSO index alone would lead to the prediction of an average hurricane season, there is significant uncertainty. Overall, I consider the ENSO to mainly a neutral factor this year.

Present ocean temperatures in the Atlantic are slightly above average in the Gulf of Mexico and Caribbean, and significantly above average in the subtropical Atlantic and near the U.S. east coast. However, there is a large area of below average temperatures in the tropical Atlantic which is forecast by long-term models to possibly persist for a few months. The tropical Atlantic has also been dry and stable, in contrast to elevated storm activity in the Caribbean and Gulf of Mexico. These trends also show some signs of persisting into the beginning of hurricane season. I therefore expect a slow start to the season in the main development region of the tropical Atlantic (extending from Africa to the Caribbean) and a corresponding lack of Cape Verde or long-track hurricanes, though these could appear more in late September and October. There is significant potential for formation in areas closer to land, so I expect some shorter lived hurricanes in the northern Caribbean/Gulf of Mexico and U.S. east coast regions.

My estimated risks for different parts of the Atlantic basin are as follows (with 1 indicating very low risk, 5 very high, and 3 average):

U.S. East Coast: 5
The jet stream over the U.S. has been weaker than usual so far this season, and the Bermuda high stronger. However, with a weak El Nino possibly developing, long hurricane tracks westward into the Gulf still seem unlikely. The east coast, in contrast, is at a greater risk. Ocean temperatures offshore are anomalously warm and region will be very moist, suggesting a fairly high probability of tropical cyclone impacts.

Yucatan Peninsula and Central America: 3
The western Caribbean shows some signs of being a fertile area for cyclonogenesis, but with prevailing upper-level patterns as they are, it is difficult to see strong system taking due westward tracks into central America. Compared to the last few years, strong hurricanes are less of a threat, though the potential for flooding rains may be equal or greater.

Caribbean Islands: 2
As discussed above, the main development region may remain quiet for at least the first half of hurricane season. This would insulate the Caribbean islands from the approach of Cape Verde hurricanes to the west, but does not preclude development occurring locally. Nevertheless, it is somewhat more likely this year that the islands will receive a break from intense hurricane landfalls, especially the easternmost islands.

Gulf of Mexico: 3
Factors in the Gulf point in different directions. Ocean waters are warm and will likely continue to be so, particularly in eddies originating in the northern Caribbean (which also happens to be a likely source of Gulf hurricanes). On the other side, if an El Niño does develop, the Gulf of Mexico is where the suppression of hurricane activity would be most felt. Putting this together suggests a near-average risk this year.

Overall, the 2018 season is expected to be a bit above average; it should not be a repeat of the devastating 2017 season, but many areas such as the U.S. east coast may still be at high risk. Further, this is just an informal forecast and uncertainty in the outcome remains significant. Everyone in hurricane-prone areas should still take due precautions as hurricane season approaches. Dangerous storms may still occur even in overall quiet seasons.

Sources: http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf, https://www.tropicaltidbits.com/analysis/models/?model=cfs-avg, https://ocean.weather.gov/