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
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.
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).
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 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 2nd 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 or stronger 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 date, it looks like 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 200 to 240…
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. This could also enhance the
severe risk this Summer.
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.
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.
