Forecast for Florida’s hurricane season in September: The calm will not last
It’s hurricane season. How well do you know the tropical terms?
It’s hurricane season. How well do you know tropical terms?
A Category 5 hurricane in the Caribbean in July. Aurora in Florida. The Houston derecho. An earthquake in Tewksbury, New Jersey. Two EF-2 tornadoes sweep through Tallahassee.
There has been no shortage of extreme and rare natural phenomena on our planet in 2024. But now it is time for the most unusual, unforeseen and bizarre weather event yet: the Labor Day weekend with no immediate threat of hurricanes in the USA.
From Frances to Irma to Dorian, Labor Day weekend is typically a time of either maximum excitement or wound-licking after a recent tragedy like Andrew, Katrina, Hermione, Harvey, Laura, Ida or Idalia.
Even the strongest hurricane to ever hit the US highway bears his name: the Labor Day hurricane, which split the Middle Keys in 1935 with sustained winds of 300 km/h.
Contrary to expectations, there have been no named storms in the Atlantic this year since Ernesto disappeared ten days ago.
This is a significant absence, as about 15% of historical hurricane activity in the U.S. falls in the two-week period between August 20 and September 2. The fact that we are currently neither in cover nor in quiet doesn’t mean it will remain permanently quiet (more on that later), but there is value in staying away from this part of hurricane season.
WHO IS THIS? A look at the prime suspects who killed potential storms
What caused potential storms to die down? Well, I can tell you that every hurricane forecaster and researcher is more than a little stumped trying to figure that out. Let’s take a look at possible suspects, murder mystery dinner theater style.
El Niño/La Niña
In general, an El Niño, or anomalous warmth in the central equatorial Pacific, leads to fewer and weaker hurricanes in the Atlantic, and La Niña means just the opposite.
A La Niña phenomenon expected in 2024 is starting more slowly than expected, but the El Niño/La Niña region is still significantly cooler than the surrounding Pacific, and western Atlantic shear is low as a result.
That doesn’t seem to be the problem.
Sea surface temperatures in the Atlantic
In recent weeks, a persistent notion has spread online that the Atlantic is “cooling rapidly.” This is far from reality, as the main developing region of the Atlantic remains the warmest region on record, warmer since 2023, and has even heated up further in recent weeks.
From the Gulf through the Caribbean to the eastern Atlantic, wide and deep warm waters await, providing a rich source of energy to any disturbance that can take advantage of them.
But there may be some truth to this misconception. An area of the Atlantic Ocean along the equator south of Nigera is slightly cooler than the surrounding waters, which could throw off another factor in hurricane formation.
Tropical convection and tropical waves
In recent weeks, numerous strong tropical waves have been moving across Africa, the breeding ground for hurricanes. But perhaps because of the greater temperature differences between the heat south of the Sahara and the milder waters near Africa, the zone of colliding winds that these waves follow is much farther north than usual this August.
This summer has brought heavy rains even to normally dry southern Algeria and Libya, where thunderstorms are as out of place as a Dave & Buster’s in a Florida state park.
This means that rather than rolling gently off the coast and moving westward, these waves further north have become caught in the strong West African monsoon winds, blurring their initial rotation and preventing subsequent development. Their northward shift also means the waves are forming over cooler waters and closer to the adverse influences of mid-latitude weather. And that brings us to our final suspect.
Influences of the middle latitudes
Dry air is a typical problem in the tropical Atlantic in August, especially when combined with Saharan dust. However, the problem recently has not really been desert dust, but rather repeated dips in the jet stream over the northeast Atlantic, which have pushed huge swaths of bone-dry air onto the north side of the tropical waves.
This is a rather strange and atypical pattern for the North Atlantic jet stream, but it effectively suppresses convection, the building blocks from which storms form.
The real highlight could be all this
So is El Niño in the western Atlantic with shear the culprit? Or anticyclonic breakwaters in the main developing region with dry air? The real answer is that many factors are probably at play, to an extent that can only be clarified after the season.
But in general, hurricane formation is like baking: You need flour, sugar, milk and eggs, plus a heat source, to bake a cake, and tropical storms need low- and mid-elevation moisture, favorable upper-altitude winds, runoff and warm oceans. In recent weeks, the Atlantic has been lacking the moist ingredients. The result is not atmospheric layer cakes, but a disaster of dry cake heated to 500 degrees in the Caribbean.
As we approach the peak of hurricane season, these rapidly changing weather factors can change in an instant. August 2024 shares a number of pattern similarities with August 2022, a month in which above-average activity was expected and no named storms developed.
September 2022 brought six storms, including Ian, and ocean heat content is much higher by September 2024 than it was two years ago.
Don’t expect a sustained slowdown in September
In fact, the winds of change may already be brewing. The National Hurricane Center is tracking a tropical wave in the central tropical Atlantic that may emerge from the purgatory of dry air over the next week and possibly enter the Caribbean, where it will continue to strengthen.
It’s by no means certain, but the uncertain currents late next week could make this one to keep an eye on for the U.S.’s sake if it can actually develop. The models are pointing a little more strongly to eventual organization than they were a few days ago, so stay tuned.
Due to disorganized thunderstorm activity, the western Gulf Coast will also remain very wet over the next seven days, and additional tropical waves could slowly form in the eastern Atlantic in early September.
Could the Atlantic remain calm in September despite all the adversities? It’s possible, but I doubt it.
If so, we should be grateful for this rare victory. Maybe I’ll do the Will Shortz crossword puzzles that have been sitting on my nightstand for the past eight years, or learn to play the banjo instead of just owning a banjo.
But keep in mind that the frequency of hurricanes and major hurricanes hitting Florida is essentially constant between late August and late October. More than 70% of the hurricane season is still ahead of us, and only a fool would bet that the winds will be consistent the entire time.
Keep your eyes on the skies, although I won’t blame you if you take Labor Day 2024 off.
Dr. Ryan Truchelut is chief meteorologist at WeatherTiger, a Tallahassee-based company that provides forensic meteorology expert services and subscription services for agricultural and hurricane forecasts. Visit weathertiger.com to read a version of this Outlook with more animated GIFs and learn how you can leverage our expertise.