To start last hurricane season, waters across the Atlantic Main Development Region or MDR – where most of our strongest hurricanes form during the peak months of the hurricane season – were experiencing chart-topping warmth. Nearly 90% of the MDR was at record or near-record warmth at this time last hurricane season.
It was a remarkable and unprecedented marine heatwave that began a year earlier in the spring of 2023. But since the beginning of 2025, the MDR has cooled significantly, with water temperatures falling to near seasonal averages from the Caribbean to Africa. A paltry 6% of the MDR is at record or near record warmth this week.
It’s a striking and welcome turn of events to start the new hurricane season and may portend a less active overall season in 2025 than we’ve observed in recent years.
New paper unpacks 2023’s unprecedented Atlantic heatwave
A new peer-reviewed paper published on Wednesday in the esteemed scientific journal Nature by a team of Australian and German climate scientists, oceanographers, and meteorologists, explores the driving factors behind the extreme heatwave across the North Atlantic that took off in 2023.
While several factors were at play – including background global warming, reduced Saharan dust cover, and a developing El Niño in the eastern equatorial Pacific – the biggest driver was a weaker than average Bermuda High that reduced the typically brisk east-to-west moving trade winds that blow from Africa to the Caribbean. This reduced ocean mixing and rapidly warmed Atlantic waters.
We wrote about this extensively the past few seasons and identified the weaker trades as the culprit of the warming at the time, now confirmed by months of peer-reviewed research.
Here’s how I described it in the daily newsletter on June 28, 2023:
“The source of the spike is largely a change in the jet stream pattern that weakened the semi-permanent subtropical high pressure over the Atlantic. Since May, this persistent pattern slowed the brisk east-to-west flowing surface trade winds from Africa to the Caribbean, reducing ocean mixing that typically keeps surface waters from overheating.”
“To add fuel to the ocean fire, outbreaks of Saharan dust which might veil sunlight as dust cover peaks in June and early July have been largely absent since April. The result is the warmest Atlantic we’ve seen this early in the season going back at least 43 years.”
This is exactly what the peer-reviewed research now confirms.
Will the Atlantic cooldown persist?
Atlantic waters have begun to take on a pattern that’s often less conducive to very active seasons, with cooler than average waters in the deep tropics and warmer than average waters in the subtropics.
An updated 2025 hurricane season outlook was just released Thursday by the European Centre for Medium-Range Weather Forecasts or ECMWF – the group behind the famed Euro model – calling for an overall average Atlantic hurricane season ahead, with between 10 and 17 named storms (the 30-year average is 14 named storms).
Average activity this season would be consistent with the pattern of water temperatures we see today across the North Atlantic. However, it’s worth noting that ECMWF hurricane outlooks aren’t especially skillful at this range and they have missed appreciably in years past, like in 2020 when they indicated an average year but the season ended as one of the most active on record.
At least for the foreseeable future, forecast models predict strong trade winds will persist due to a stronger than average Bermuda/Azores High.
This plus the expansive Saharan dust plume, which acts as a big sun shield, should keep waters from warming very much for most of June.
All quiet for now
The Atlantic will stay quiet to round out the first full week of the hurricane season, with no signs of activity at least into the middle part of next week.
