- A tropical wave, designated 91L, is developing in the Atlantic and could become a tropical depression by the weekend.
- This system poses a potential hurricane threat to the Lesser Antilles and Puerto Rico by mid- to late next week.
- While the first half of the 2025 hurricane season has been quieter than average, the second half is forecast to be more active.
Like the location of bread in a Costco, the weather is never the same from week to week. Fortunately, as we approach the halfway point of hurricane season 2025, the main source of excitement in life thus far this year has been new items at the Costco food court, rather than storm threats.
The can pyramid I make from the LaCroix I drink while writing tropical forecasts – already suitable for providing a pharaoh with ample sparkling waters for the afterlife at this time last year – would be humiliating to even a mediocre vizier in September 2025, much less a grand vizier.
However, unlike last week, the Atlantic is not devoid of features worth watching. The key area of interest today is a tropical wave, designated as 91L by the National Hurricane Center, in the Atlantic’s Main Development Region about 1,500 miles east of the Lesser Antilles.
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91L: A mid-September tropical threat to the East Coast can't be ruled out
Storm activity associated with this disturbance has gotten more concentrated over the last couple of days, with convection consolidating far enough south to mostly dodge unfavorable dry air and wind shear to its northwest. Expect a tropical depression to develop from this wave by Friday or Saturday as it moves generally west or west-northwest.
In the medium term, 91L poses the first real threat of the season to the Lesser Antilles and Puerto Rico. With upper-level lows lurking to the north, it is possible that the storm could be deflected well north of the islands, or weaken as it encounters stronger wind shear.
However, should 91L keep consolidating farther south, it could well strengthen in a favorable environment through early next week. Some degree of a north turn is probable as the system nears the eastern Caribbean, but I would watch the forecast carefully from Barbados to the Dominican Republic for a possible hurricane threat mid- or late next week.
At long range, it’s not clear what the fate of 91L will be, should it survive the various pitfalls of the next week to ten days.
A persistent dip in the jet stream over the eastern U.S. that has brought an unseasonable chill (and made me want to run through the halls of Spirit Halloween) should remain in place for another 8 to 10 days, but weaken thereafter.
As usual, the most likely eventual outcome is a path well east of the U.S. East Coast, but there’s enough uncertainty in where the storm will be and what the steering current pattern will be like beyond next week to make the situation worth lightly monitoring for U.S. interests.
It’s just that time of year.
Long-term forecast on track: Back half of hurricane season could be brutal
Otherwise, the Atlantic is quiet, and tropical development is unlikely through the midpoint of hurricane season around September 10th. Depending on what the tropical wave does, that means we’ll reach halftime with 6 or 7 tropical storms, 1 or 2 hurricanes, and 40 to 50 units of Accumulated Cyclone Energy (ACE) under our belts — all a little below average for the last 75 years.
That’s not a surprise. In WeatherTiger’s late July hurricane season outlook, I anticipated that the first half of the season would “rack up fewer than 50 ACE units” due to marginal upper-level winds.
So far, so good. However, I wouldn’t mind being wrong about the accompanying prediction for the second half of the season, which was that it would “clock a well-above-average 80 or more ACE units.”
WeatherTiger’s real-time seasonal outlook algorithm continues to suggest a busier than normal September, October, and November in the Tropics.
In terms of continental U.S. hurricane chances, six weeks ago the most likely outcome was 2 or 3 landfalls; now, as the U.S. passes our historical halfway point unscathed, that’s declined to a 50% chance of 1 or 2 hurricane landfalls and 30% chance of zero hits. Odds of a continental U.S. major hurricane strike are down as well, but remain about 35%. That’s above average for the second half of the season.
Fundamentally, the reasons behind this backloaded outlook remain as I laid them out in late July. Water temperatures in the Central Pacific have continued to cool through August, suggesting that models are correct in predicting a weak La Niña event will emerge there in September or October.
That typically means lower than normal wind shear in the Gulf and Caribbean in the final third of hurricane season, a common element of the La Niñas that juiced the busy 2020, 2022, and 2024 late seasons. Additionally, the western Atlantic, Gulf, and Caribbean have all warmed to well above normal.
In general, the global map of August sea surface temperature anomalies closely resembles the pattern historically associated with a busy September, October, and November across both the Atlantic and Pacific. You can check out daily updates to our seasonal outlook models at weathertiger.com now through mid-October.
Overall, the clucking of meteorological drama queens to the contrary, it’s been a quiet, hopeful first half of hurricane season: for instance, FSU wins have a decisive 1-0 edge on Florida hurricane landfalls, following a catastrophic 3-2 defeat in 2024. Unfortunately, there are distant signs of trouble brewing, with La Niña rising and 86° to 88°F Gulf water temperatures once again a powder keg in search of a spark (perhaps Alabama fans can cool it off with their tears).
I’ve got my Costco pallets of LaCroix backed up with an emergency supply of AriZona teas, and you should keep your hurricane kits and plans similarly primed for action as we roll into the second half of the season. Keep watching the skies.
Dr. Ryan Truchelut is chief meteorologist at WeatherTiger, a Tallahassee company providing forensic meteorology expert witness services and agricultural and hurricane forecasting subscriptions. Visit weathertiger.com to learn more. E-mail Truchelut at ryan@weathertiger.com.
