Hurricane outlook part three

 

Here is part three of 2024 Atlantic hurricane season outlook.

The Atlantic hurricane season officially starts in 31 days. And many want to know what looks to happen. This multipart series as tried to bring you just that. But now is the time to prepare for what could be a busy season. This will be the final part of this multipart hurricane season outlook.   

You can find the first two parts here

Part one

Part two

In those two parts I emphasized the two main factors that will greatly influence how much tropical activity we see in the Atlantic basin this season.  The first is the El Nino Southern Oscillation (ENSO). The second are the well above average sea surface temperatures (SST) in the tropical Atlantic.

I was going to just show basic numbers for the final part of the hurricane outlook. But I’ve decided to do the opposite, and dive into details I didn’t cover in parts one and two. So, if you want to avoid the data and how I’m arriving at my conclusion, you can skip to the end.

This outlook is probabilistic in nature, meaning the stated outcomes fall within a certain likelihood of occurring. It is based on meteorological scientific principles and my understanding of the current global weather pattern and how I think it will evolve. As always, I’ve tried to make everything as easy to understand as I can.    

At the end of this outlook, I will include a look at what our summer pattern might look like.

SST:

 

The Pacific Ocean …

When we look at SSTs, we can see the equatorial eastern Pacific is much cooler than it was a few months ago. So, the El Nino is rapidly weakening. We can also see those above average SST in the Northwest Pacific around the Aleutians with the colder SST in the Gulf of Alaska.   All of this is going to have huge implications on this year’s Atlantic hurricane season.

El Nino Southern Oscillation (ENSO)…

The ENSO sets up a weather pattern that can help predict a strong or weak Atlantic hurricane season. These two phases are called El Nino and La Nina.  EL Nino tends to increased vertical wind shear (the change in wind speed and direction with height) over the Atlantic, this makes it hard for tropical cyclones to develop and strengthen.  La Nina tends to favor lower vertical wind shear; it is generally correlated with a busy Atlantic hurricane season.

Below is an image that shows where the ENSO 1+2, 3, 3.4, and 4 regions are located.

 

Region 1+2 is the smallest and farthest east. Regions 3 and 4 cover the east and west and together cover a large part of the tropical Pacific. Most analyses and forecasts are focused on a combination of regions 3 and 4, seen on the image as the main Nino 3.4 region.

El Nino: characterized by a positive ONI greater than or equal to +0.5ºC.

La Nina: characterized by a negative ONI less than or equal to -0.5ºC.

By historical standards, to be classified as a full-fledged El Nino or La Nina episode,

these thresholds must be exceeded for a period of at least 5 consecutive overlapping 3-month seasons.

The CPC considers El Nino or La Nina conditions to occur when the monthly Nino3.4 OISST departures meet or exceed +/- 0.5ºC along with consistent atmospheric features. These anomalies must also be forecasted to persist for 3 consecutive months.

La Nina is really ramping up.  The La Nina is developing even faster than was expected. As El Nino continues to collapse, we’re close to neutral conditions (we could be neutral already).  But at this time, La Nina conditions are expected to take over by the summer and last well into the winter of 2024-2025. Right now, it looks like we will likely have at least a weak La Nina for the peak of the Atlantic hurricane season (August-October). I have see some outlets discuss how this could end up a strong La Nina. I'm not saying that will be impossible; but I think it is very unlikely. Given what I'm seeing and how I think it will evolve, a weak to moderate La Nina seems more likely, but we will see.   

Pacific Decadal Oscillation (PDO)…

We’re in a negative (cold) PDO; we know this by the warm SST in the Aleutians and the cold SST in the Gulf of Alaska. This is very important, as negative PDOs tend to enhance the La Nina pattern.

 

A negative PDO generally supports a ridge in the Gulf of Alaska and a trough in the western CONUS into the Plains. It also has a tendency to enhance the southeast ridge in the eastern CONUS.  

Typically, during a negative PDO…

The polar jet stays active which will Increase the risk for severe weather in the Plains, Mississippi River Valley Upper Midwest Tennessee River Valley and Ohio Valley. We've already seen this over the 7 to 10 days.

We also Characteristically see strong high pressure near the Bahamas and Gulf Coast.

This typically has the storm track shift into the Great Lakes and ends up drying out the Middle Atlantic into the Northeast. So, all the rain we’ve been getting is a good thing as it will help stave off drought.

With the shift in the storm track, there is a tendency for tropical air masses coming out of the Gulf, to work their way up the East Coast. This kind of pattern, also means we will have the northwest Atlantic influencing weather in the Northeast and northern Middle Atlantic Region. This would have impacts not only on the tropical season, but also the summer pattern in general.

 

The Indian Ocean…

The Indian Ocean is very warm. Positive (warm)/negative (cold) IOD impacts how the La Nina will interact with the atmospheric pattern, it also has some impact on the SOI.  One important aspect of the warm Indian Ocean, is it promotes strong tropical waves moving over Africa. Strong tropical cyclones over the Indian Ocean would bring the increased risk of potent tropical waves moving across Africa, that would emerge into the Atlantic, that could rapidly develop due to the warm Atlantic.  

 

The Atlantic Basin…

The Atlantic is very warm in the Tropics, with SSTs to the north much cooler. This is a result of all the upper-level lows that have been plaguing the Canadian Maritimes.

Ocean heat content in the Atlantic Main Development Region (MDR) is well above the 2013-2023 average. SST in the MDR and Caribbean are 2°C to 5°C above average. That is extraordinary for this point of the year.

 

Currently the Gulf is running average based on the 2013-2023 average. But the Gulf will continue to warm as we get closer to the heart of the hurricane season.

 

The high oceanic heat content in the MDR, means there will be plenty of fuel for tropical waves to tap into. Cape Verdie Season could be very active.

The developing La Nina, is already building a ridge in Mexico, this ridge will push into Texas and the southern Plains during May and June. So, we can expect the southern Plains to be downright hot this Summer.

The developing ridge allows the storm track to shift north, this will tend to lessen the subtropical jets influence, which has been very active. As the troughs move out of the West Coast, they will be forced to move over the ridge. As a result, there will be an increased risk for severe weather outbreaks over the Central Plains into the Ohio Valley. As the ridge continues to lift northward, the Upper Plains, Great Lakes and Northeast could see an uptick in severe weather.  I do expect to see a big uptick in severe activity in the Plains starting during the 2^nd half of May into June; as southern moisture streams north rising dew points.  We saw something similar in 2011 where the country experienced big severe events.

As El Nino wanes the eastern half of the CONUS is going to be wet. We’ve already been seeing that during March and April. We should continue to see an overall wet pattern for May into June. But then La Nina should be kicking in, and force the pattern to become drier. So, all this rain we’ve been getting would help reduce the risk for excessive drought this Summer.

The ridge axis is going to be very important. If the axis sets up over the East Coast. This would increase the drought potential.  With the tropical Atlantic looking to be very active. That kind of pattern would have these tropical systems moving into the Gulf. Then as the ridge axis shifts, the tropical systems and remnants tend to drag a lot of moisture up into the Middle Atlantic and Northeast. We saw similar tracks in 2011 with storms like Irene and Lee. 

 

La Nina….

La Nina patterns typically favor more tropical activity in the Atlantic due to the lack of wind shear. Strong wind shear, or the change in wind speed/direction with height into the atmosphere, will usually tear some storms apart and prevent many from forming in the first place. However, this year, that lack of strong wind shear and unusually warm sea surface temperatures could combine to produce a near-record hurricane season.

I’ve been getting a few questions about how sure I am about La Nina developing by this fall? Some people with the Australian Bureau of Meteorology (BOM) have been saying we might not have a La Nina this year at all.  Even though anything is possible. I’m very convinced we will see a La Nina develop. This belief is based not only what’s going on the Pacific, but also in the Atlantic.  The tropical Atlantic being so warm is part of the reason, that the equatorial Pacific is cooling so quickly. Research has shown those warm SST create pressure differences between the Atlantic and the Pacific. This leads to zones of high pressure in the upper atmosphere over the Pacific and low-pressure zones near the surface. These differences produce a setup that increases trade winds over the eastern into central equatorial Pacific. The faster winds lead to cooling of the SST in the eastern Pacific. This is accomplished by something called the Matsuno-Gill response. This is also the likely reason La Nina events have become more common and El Nino less so over the last 10-15 years. So, this is making the change to La Nina even more likely.

La Nina could end up moderate  by the heart of the season. So, things could be very active during the 2nd half of the season.

Rapid intensification (RI)…

The SST in the tropical Atlantic are very warm, with La Nina looking to form in time for hurricane season; the setup in the Atlantic supports the chance for storms to rapidly intensify. 

RI occurs when a tropical cyclones winds increase by at least 35 mph in a 24-hour period.

Wild Cards:

2024 is unique in many ways.  These things are making things harder to interpret.  We just had a three year La Nina, then we had the strong El Nino that has basically ended. If we do see La Nina return this year; that would be the first recorded time this pattern has been seen. I will touch more on this later in the write up. But I’m sure we’re going to see some surprises because of these things.

La Nina can bring lots of Saharan Air Layer (SAL) in the Atlantic, we dealt with this in 2022…this is a big unknown. SAL is dry dusty air that blows off of North Africa on the trade winds. The layer overlies the more humid air. This creates an atmosphere this is more hostile and causes developing storms to struggle.  Currently there is a lot of SAL over the eastern Atlantic.

There has been an extreme heatwave in the Sahel region and West Africa in March and April. Looking at the data, it looks like there will be much less rainfall for western Sahel during the Monsoon season, with perhaps more rain over central and eastern Sahel during the wet season. With severe drought over northwest Africa, there is a high likelihood for an increased chance for dust transport from those areas. So Saharan dust over the Atlantic could be above average at times.  

The strength and placement of the Azores/Bermuda High will be very important on the overall tracks of tropical cyclones.

The Atlantic is boiling (figuratively speaking), we’ve never really seen the Atlantic this warm especially the eastern Atlantic. These warm waters will have an impact on the overall wind pattern. These warm SST make it difficult to look to the past to get an overall picture for this season.  So how the cause and effect of all of this will affect the steering pattern and how tropical cyclones behave this season is unclear.  

 

Analogues:

Looking back at the historical record, there are certain years that have oceanic and atmospheric setups that are similar to this year. Yes, the SST in the Atlantic are warmer than we’ve ever seen. But in spite of that, looking at this can give us insight as to what the coming hurricane season may look like.

These seasons followed El Nino and saw La Lina in place by the heart of the hurricane season. These seasons also had similar SST patterns across the globe.

These nine years seemed to be the closes matches to this year’s overall SST footprint.   1878, 1926, 1970, 1975, 1998, 1999, 2010, 2011, 2020

I narrowed those years down to 1970, 1975, 1999, 2010, 2011, 2020

The historical Atlantic La Nina track density shows the western Atlantic Basin is busy during La Nina seasons. 

  

An outline of what all of this means:

Another important fact, is that during El Nino the overall pattern tends to make it much more likely for tropical cyclones to stay out over the open Atlantic. This overall idea, reverses during La Nina. So, the odds of tropical cyclones to make it into the western Atlantic Basin, vastly increasing the risk for landfalling systems on the U.S. main land increases.

The SSTs in the tropical and eastern subtropical Atlantic are at record highs. Give that the trade winds over the Atlantic have been below average, this has greatly added the water to become very warm due to less evaporation and upwelling of the cooler subsurface water. With La Nina taking over, trade winds should continue to be weak, which will allow SST to warm even more.

As I said above, those record warm SST in the Main Development Region will be a catalyst for more and stronger hurricanes. But there is a chance those SSTs could be a dual edged sword. The stronger hurricanes become the more likely they are to pull north. If this happens it could keep some of the stronger hurricanes away from the Caribbean and U.S. Mainland.  This will greatly be affected by what happens with the Azores/Bermuda High.

We’re going to see at least occasional SAL intrusions into the Atlantic Basin this season. How extensive these dust/dry air outbreaks are going to be remains to be seen.

All signs are pointing at a robust Azores/Bermuda High in the Atlantic this year. If this happens there would be increased odds of tropical cyclones making their way into the Western Atlantic Basin.

Above I noted that the SST in the tropical Atlantic are very warm, while the SST to the north is cooler. There is a chance this temperature difference, allows for higher wind shear than is being anticipated. This is something we will have to watch.

When we look at the Euro precipitation anomaly for the heart of the hurricane season; we see a lot of precipitation in the Caribbean into the Gulf and along the East Coast.

The NMME model is showing the same support for a lot of tropical activity in the Caribbean into the Gulf as well as up the East Coast.  

The States of Texas, Louisiana, and Florida look to have the highest probability of a major hurricane making landfall this season.

The NMME SST anomaly is showing support for a moderate to perhaps strong La Nina for the Summer into Fall hurricane season.

 

My Call:

Many outlets are calling for a record-breaking number of Tropical cyclones for this upcoming hurricane season. You can find what some of the other outlets are saying in part two of the outlook. NOAA won’t release their outlook until later in May.

While I believe this season will feature well above average activity.  The wild card factors I went over will have an impact. This will be especially true when it comes to SAL over the Atlantic.  I think we’re going to be ending up dealing with SAL at times; this is going to help curtail development and strength of tropical cyclones that form out of the African waves; this should keep the 2024 season out of the record books when it comes to overall numbers of named storms. For that reason, my numbers will be a bit lower than some of these other outlets.

Named Storms… 17-25

Hurricanes… 8-12

Major Hurricanes… 4-8

Accumulated Cyclone Energy 150 to 210…

Summer 2024:

A general overview of how this summer looks to unfold. 

Summer in the Northeast and Middle Atlantic is greatly affected by the tropical activity in the Atlantic Basin. So, the same analogues I’m using for the hurricane season, can also be used for the summer outlook.

During the Summer we’re going to be dealing with the Southeast Ridge along with the northwest Atlantic.  Moisture will be streaming up the East Coast. But we also have those colder pockets of cold water off the New England Coast into the northwest Atlantic along with warmer water off the Middle Atlantic Coast. This is going to setup a temperature gradient between the Gulf Stream and those colder SST off of New England. This is likely to lead to areas of upper level low pressure setting up over Atlantic Canada as well as stronger areas of low pressure setting up time to time off the Middle Atlantic and track toward the Canadian Maritimes.

 

Temperatures…

Here is a look at what to models are indicating for the overall temperature pattern for the Northeast and Middle Atlantic.

 

So, while La Nina’s have a tendency to produce warmer summers, what’s going on over the Canadian Maritimes could send back door cold fronts into the Northeast, which might help counter the warm air surging northward. at least for the first part of June. Toward the end of June into the end of August could end up quite warm to hot at times. September should be a bit cooler, but overall it will most likely end up slightly above average.  As the southeast ridge becomes more dominate. Frontal systems moving through, they would be moving into warmer and more humid airmasses. This could enhance the severe risk this Summer. I still think the severe season in the Northeast will be quite active with a lot of chances for tornadoes, but overall this summer will have a tendency to want to be quite warm. We will see.

 

Precipitation…

When we look at the six analogue summers, they show the propensity for above average rainfall over the Middle Atlantic Region into the Northeast.

 

This is because to the increased potential for moisture to stream north over the eastern U.S.  Just how much rainfall the Northeast and Middle Atlantic gets will, depend on how the tropical systems track. With the Atlantic looking to see an above average season there is an increased danger from tropical cyclones making direct or indirect impacts. With the 2nd half of Summer looking to be warmer, we could see  drought issues develop during  July, August and September. But again, tropical moisture could negate that. Drought this Summer is going to be a battle between the heat, and tropical moisture making it into the region. how much tropical moisture we see, will be a major factor in how dry we end up.  

Well, that’s it. I hope you found this informative and interesting.

I will be happy to answer any questions you may have. If you have questions, you can ask them in the comments here or on my Facebook weather pages.