TLDR: It’s too early for a reliable seasonal forecast. Other than out of curiosity, it’s a waste of your time to spend much energy them. For “news” organizations to spend much time reporting on them is fear mongering or click-baiting. Come back in June, or better yet, early August.
Still here? Ok, well, ok, here’s a longer discussion. There are at least three separate aspects in doing a hurricane season forecast: the number of storms, the intensity of those storms, and where those storms are likely to go (which is all that matters for impacts). While there is some relation between the three aspects, they don’t interact in completely obvious ways. You can have 25 storms in a season – but if they are all “fish storms” and don’t make landfall, impacts are minimal. On the other hand, a season like 1992 with only six storms matters a lot since one of those storms was Hurricane Andrew.
There are two major “big picture” items that set the overall tone for a season and to a great extent control those first two aspects (how many/how strong). These are the state of the El Niño/Southern Oscillation, or ENSO cycle, and the sea surface temperature (SST). The first (ENSO) controls the upper air conditions and thus things like wind shear, humidity, etc. that influence storm formation and growth, the SST controls how much energy is available to power the storms. The forecasts you have been seeing are based largely on forecasts using the current SST anomaly (how far it is deviating from climatology) and the ENSO forecast. Let’s take a look at each.
There are three phases to ENSO, called El Niño, Neutral, and La Niña. The names were given to the phases by fisherman in the eastern Pacific, who noticed the cycle long before meteorologists did. In general, during an El Niño summer/fall, there tends to be fewer hurricanes in the Atlantic. This is due to stronger wind shear and stability, which tends to make it harder for storms to form. La Niña has the opposite effect – conditions are usually quite favorable. Neutral years are not, as you might expect, in the middle, but actually tend to have more storms than the long term average. This is because El Niño years really drag down the long term average number of hurricanes, especially at some sites like Savannah (this effect is known as the “Flaw of Averages“). El Niño years aren’t just quieter than average, they tend to be a lot quieter than average.
The forecast for this year is for it to be a transitional year. According to the latest NOAA forecast, while we are still in an El Niño right now, a transition from El Niño to ENSO-neutral is likely before June 2024 (83%chance), with the odds of La Niña developing by August 2024 (62%chance). If so, that would mean we would be in a La Niña during the heart of the hurricane season, and that’s bad. HOWEVER … forecasts at this time of year, while they have improved some, are still subject to what is called the “spring barrier.” ENSO forecasts for the upcoming year generally stink until May – here is a link to a NOAA blog post on the subject. So while the current forecast is for a transition to neutral (which seems pretty likely), and the majority of models indicate only a brief period of neutral conditions before a La Niña starts, a complete flip isn’t carved in stone yet.
The latest CFS2 ensemble members show a longer period of neutral conditions, and not so strong of a La Niña during the season. So until we get another month or so of data, it’s way too early to invest in Beef Jerky or Florida Man Meme futures.
What about SST’s, the energy source? That is a bit more clear. The Atlantic is very warm and will probably stay that way. Here is the current SST Anomaly (deviation from normal) for the Caribbean …
Assuming that persists throughout the season (which is likely), it means that a storm forming in the West Atlantic or Caribbean, and parts of the Gulf of Mexico, would see at least a Saffir Simpson Category boost all things being equal. So that is an area of real concern – but, again, the storm has to form first, and have favorable atmospheric conditions before it can draw on that energy.
The other thing to keep in mind is that the two “big picture” items only set the stage and create opportunity. Small scale transient features of the atmosphere control if a storm spins up at a given time. One example of this is the air flow off of Africa. If storms develop that push dry air over the central Atlantic (which is often seen as dust embedded in that dry air), then storms can’t form out there. There are lots of other day to day factors that can cause a storm to explode, or die off and never form. While there are some patterns, the actual tracks individual storms follow are also complex. So knowing who is at greatest risk in any given season can be expressed in probabilistic terms, honestly that doesn’t do you any good in terms of what you should do in terms of preparation. It has some use in the commodities markets given our casino-like stock markets if you’ve got money to bet, but that’s about it.
So the bottom line is that until we have a firm handle on the ENSO state for the core of the season, we really won’t know how things will shape up. The high SST’s are a concern: there looks like there will be plenty of energy out there to spin up whatever can get itself organized. And if conditions revert to ENSO Neutral, as expected, there is the potential for an above average season. If a La Niña starts, there is the potential for a very active season, however, that’s not the whole story, and there is nothing really that says we are in store for a record setting season; that’s pure speculation and click baiting.
Bottom line, as of now in early April, conditions are good for an average to above average season, but it’s way too early to speculate on how much until the models get past the “spring barrier”. Numbers are just guesses.
As I always advise, treat each season as if you are going to get hit. You don’t care if there is one storm or twenty-one, if that one storm is a bad one and hits you. So go ahead and make sure you have a plan, especially make sure your insurance is up to date (including flood insurance) since these have a lock-out period once the season starts. There are some good checklists on the FEMA web site, at www.ready.gov.
Otherwise enjoy the spring weather!
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