As we discussed in the daily newsletter last Thursday, the tropical Atlantic has undergone a major cooldown so far in 2025, from unprecedented warmth in 2023 and 2024 to now near-average conditions across the Atlantic Main Development Region or MDR.
Waters are the coolest we’ve seen them across the deep tropics for this time of year in 4 years.
It’s worth noting that the cooling is relative to the warmth of 2023 and 2024 and this is by no means a hurricane season killer.
In fact, experts at Colorado State University on Wednesday kept their numbers unchanged for an active hurricane season.
Nevertheless, the rate of the cooling across the MDR has been remarkable since around January, when waters continued to run over 1.5°F warmer than the long-term averages (waters 1°F warmer than average in the tropics is very warm; anything above 1.5°F is exceptionally warm).
Since then, the departures from average have plummeted, largely due to a much stronger than average Bermuda high pressure.
The semi-permanent high-pressure system that stretches between Bermuda east of the U.S. and the Azores Islands west of Portugal – known as the subtropical high or Bermuda/Azores high – has been much stronger than usual in 2025.
Winds flow clockwise around the subtropical high and the base of the high pressure area is responsible for the east-to-west flowing trades winds that steer storm systems from Africa our way.
When the subtropical high is stronger than usual, those trade winds flow faster. The faster trade churn up the waters of the Atlantic Main Development Region and help to cool it.
That’s exactly what we’ve seen so far in 2025, with trade winds the third strongest on record behind only 1989 and 2009.
In contrast, trade winds across the MDR to start 2024 were the fourth weakest in the 47-year record, trailing only 2010, 2005, and 1979 (in the modern record, other than 2023 and 2024, 2010 and 2005 were two of the warmest years in the Atlantic).
Whether or not the subtropical high stays strong this season is to be seen, but longer-range models suggest it generally does, which would favor either a continued cooling or at least a continuation or more typical warmth.
We’ll need to keep an eye on the subtropical high, however, as an extension could permit storms that form to travel farther west this season.
We can’t know the important details of steering patterns until closer in to a possible storm threat, but we’ll keep an eye to the stickiness of the subtropical high deeper into the hurricane season.
Activity stays in the eastern Pacific for now
As we previewed 10 days ago in the newsletter, the stormy side of the Madden-Julian Oscillation or MJO – a see-saw pattern of rising and sinking air that makes its way around the globe about every month or two – is spreading into Central America and toward the Caribbean.
This will increase storminess from the eastern Pacific into the western Caribbean and southern Gulf next week.
The MJO, however, is much weaker than models forecast a few weeks ago, and for now most models keep activity on the eastern Pacific side.
We’ll watch the western Caribbean and Bay of Campeche next week for any organized storminess, but should any mischief happen, it would likely head west and stay well away from Florida.
CLICK HERE to download the Local 10 Weather Authority’s 2025 hurricane survival guide.
