*2025 Tropical Season and Summertime Outlook*
Paul Dorian
Sea surface temperature (SST) anomalies as of April 1, 2025. (Map courtesy Canadian Met Centre)
Overview
The number of named tropical storms in 2025 is likely to be nearly-normal in the Atlantic Basin which would be lower than the totals of last summer’s active season. The average number of named tropical storms in an Atlantic Basin tropical season is 14.4 with 7.2 of those reaching (minimal) hurricane status, and 3.2 reaching “major” classification (baseline period 1991-2020). Based on the overall analysis of current and forecasted conditions, I expect around 15 named storms in the Atlantic Basin this tropical season with about 7 reaching hurricane status and of those perhaps 3 to achieve “major” classification level.
Three important factors in this year’s tropical outlook include an expected relatively neutral signal in the tropical Pacific Ocean with respect to sea surface temperatures (SSTs), only moderately warm water temperatures anticipated in the Main Development Region (MDR) of the Atlantic Ocean, and a stubborn pocket of colder-than-normal waters off the west coast of Africa. While the lack of any kind of significant El Nino (warmer-than-normal water) in the tropical Pacific typically favors an active tropical season in the Atlantic Basin, the water temperatures in both the breeding grounds region of the Atlantic Ocean and those just off the west coast of Africa should act as a counterbalance.
In terms of summertime weather expected across the continental US, there is an especially strong signal for hot and dry conditions across the nation’s heartland from Texas-to-North Dakota which is being primed by an unusually dry spring in much of that part of the nation. Also, there is the potential of wetter-than-normal weather in much of the eastern US to go along with nearly normal to slightly below-normal temperatures and, in the western US, nearly normal temperatures and rainfall amounts.
A list of names to be used for tropical storms/hurricanes in the 2025 Atlantic Basin tropical season. (Note – the Atlantic Basin includes the Caribbean Sea and Gulf of America in addition to the Atlantic Ocean).
Executive Summary
Nearly normal number of named tropical storms, hurricanes, and “majors”
Neutral signal with respect to SSTs in the equatorial Pacific Ocean
Downward trend this year in sea surface temperatures across the Atlantic Ocean’s Main Development Region (MDR) and now in below-normal territory
A pocket of colder-than-normal water off Africa’s west coast
An analysis of “analog” years suggests the following:
Very hot and dry conditions across the nation’s mid-section from Texas-to-North Dakota
Wetter than normal conditions in much of the eastern US to go along with normal to slightly below-normal temperatures
Nearly normal temperatures and rainfall in the western US
Sea surface temperature (SST) anomalies as of March 28th, 2024. (Map courtesy Canadian Met Centre)
Recap of the 2024 Atlantic Basin tropical season
The 2024 Atlantic hurricane season was quite active with 18 named storms, 11 hurricanes, and 5 “major” hurricanes and the first since 2019 to feature multiple category 5 storms. The 2024 tropical season had the highest accumulated cyclone energy (ACE) since 2020. Accumulated cyclone energy is a metric used to measure overall tropical activity by factoring in both the magnitude and duration of tropical cyclones.
2024 Atlantic Basin tropical storm tracks are shown on this plot, and it was an above-normal year with 18 named storms. (Plot courtesy Wikipedia)
The 2024 tropical season may be best remembered for its dramatic increase in activity from late September through October which followed an unusual lull in late August and early September. One example from late in the 2024 tropical season was Hurricane Helene which formed in late September and made landfall in Florida’s Big Bend region as a category 4 storm causing severe flooding all the way northward into Appalachia. A second system of note was Hurricane Milton which formed in the Gulf of America and intensified rapidly to become the second category 5 storm of the season...eventually making landfall near Siesta Key, Florida on October 9th as a category 3 hurricane. Interestingly, while the Atlantic Basin featured an active tropical season in 2024, the much larger Pacific Ocean experienced below-normal activity in both its eastern and western basins.
Neutral signal in the tropical Pacific Ocean
What goes on in the tropical Pacific Ocean does indeed have an effect on tropical activity in the Atlantic Ocean. El Nino, which refers to warmer-than-normal waters in the equatorial Pacific Ocean, affects global weather patterns and it tends to be an inhibiting factor for tropical storm formation/intensification in the Atlantic Basin. First, El Nino tends to produce faster-than-usual high-altitude winds over the tropical Atlantic Ocean and this increase in wind shear (change of wind speed with height) is hostile to the development or maintenance of tropical storms. In addition, El Nino tends to result in sinking motion over parts of the Atlantic Basin which also is hostile to tropical storm formation/intensification.
Compilation of computer model forecasts for El Nino Southern Oscillation (ENSO) state for the rest of 2025 with a neutral signal in the tropical Pacific Ocean. The graph shows forecasts made by dynamical and statistical models for sea surface temperature (SST) anomalies in the Nino “3.4” region for nine overlapping 3-month periods. (Dynamical models use physical equations to simulate the atmosphere and ocean whereas statistical models rely on historical relationships between climate variables to make predictions). Plot courtesy International Research Institute/CPC, NOAA, ECMWF, JMA
On the other hand, La Nina conditions in the equatorial part of the Pacific Ocean usually correlates with weaker wind shear over the breeding grounds of the tropical Atlantic Ocean and this leads to a more favorable environment for the development/intensification of tropical activity. La Nina formed in the spring of 2024 and then intensified some going into the winter season of 2024-2025. The La Nina conditions have since weakened considerably in the tropical Pacific during the first part of 2025 and numerous computer models favor the idea of nearly neutral conditions through the upcoming summer and fall seasons.
The ECMWF seasonal forecast map of mean SST anomalies for June, July, and August features relatively neutral conditions across the equatorial Pacific Ocean and only modestly warmer-than-normal conditions in the Main Development Region of the Atlantic Ocean. Map courtesy ECMWF
Moderately warm SSTs in the Atlantic’s MDR; cold pocket near Africa
Not only are Pacific Ocean sea surface temperatures important in terms of its potential impact on tropical activity in the Atlantic Basin, but Atlantic Ocean water temperatures are crucial and play more of a direct role in the prospects for formation/intensification of tropical storms. Sea surface temperatures of >80°F are generally considered to be a necessary condition for the formation of tropical storms in the Atlantic Basin. As a result, above-normal sea surface temperatures are more favorable for the formation and intensification of tropical storms as waves trek westward over the tropical Atlantic from western Africa.
The water temperatures in the Main Development Region (MDR) of the Atlantic Ocean have trended downward since early this year and have recently slid into below-normal territory. Plot courtesy NOAA, tropicaltidbits.com
Indeed, the waters in the Main Development Region (MDR) region of the Atlantic Ocean have trended downward since early 2025 and have just recently slipped into below-normal territory - a neutral signal at best for tropical storm development - and they are noticeably cooler than a year ago. In the far eastern Atlantic, colder-than-normal water currently exists off the west coast of Africa and this could act as a deterrence for tropical storm activity during at least the early part of the 2025 tropical season.
The average of five analog years (1970, 2013, 2000, 2011, 1967) that I have selected based on comparison with expected sea surface temperature anomaly patterns this summer featured an especially hot and dry summer across much of the mid-section of the nation from Texas-to-North Dakota and cooler, slightly wetter than normal conditions in much of the eastern and western US. Average temperature anomalies (top) are shown for the five analog years as well as average precipitation anomalies (bottom) for the period of June-through-September. Maps courtesy NOAA
Summertime outlook for the continental US...analog years comparisons
Based largely upon the expectation of relatively neutral conditions in the Pacific and only moderately warm conditions in the Atlantic’s Main Development Region, five analog years have been selected which featured similar sea surface temperature anomalies and trends. When averaged together, these five analog years of 1970, 2013, 2000, 2011, and 1967 suggest it could be an especially hot and dry summer across the nation’s heartland from Texas-to-North Dakota. In the eastern US, a wetter-than-normal summer is on tap to go along with normal to slightly below-normal temperatures and, in the western US, nearly normal temperatures and rainfall amounts.
An especially worrisome sign for the nation’s mid-section from Texas-to-North Dakota is that hot and dry weather conditions appear quite likely for the upcoming summer season and drought conditions already exist in much of this area. Map courtesy NOAA
Meteorologist Paul Dorian
Arcfield
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