Slow Start in Tropical Atlantic Belies Above-Normal Forecast

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Written by Aaron Studwell for Industrial Info Resources (Sugar Land, Texas)--Since the year 2000, the average date of the tropical Atlantic's first named storm has been June 3. Excluding 2016, when Tropical Storm Alex was named on January 14, the daily average slides back to June 9. With the current forecast showing no tropical development expected over the next week, 2025 is projected to be the latest start to the tropical Atlantic season since Tropical Storm Arthur was named on June 30, 2014.

Globally, subtropical oceans, particularly parts of Pacific and Indian Oceans, have surged to record warmth. However, this extreme warmth may be contributing to fewer tropical storms by creating a more stable atmosphere. Additionally, a thick blanket of Saharan dust has extended across the central and eastern Atlantic, as far west as the eastern Caribbean. The Saharan Air Layer (SAL) also extends north of the Caribbean Sea, across the Bahamas and south Florida.

The dust and dry air associated with the SAL keeps sea surface temperatures near normal levels, while also yielding lower humidity levels. At this time, all but one of the tropical waves over the Atlantic have associated convection; that wave's convection is located at a convergence point with the monsoon trough and should dissipate as the wave continues west.

Click on the image at right for a National Oceanic and Atmospheric Administration map of the Saharan Air Layer.

One factor influencing the Atlantic is a developing cooling pattern in the eastern tropical Atlantic, known as Atlantic Niña. Equatorial temperatures are averaging 1-2°C below normal between 5°E and 32°W. Recent research indicates that this emerging climate signal could suppress hurricane activity by altering atmospheric patterns and reducing favorable conditions for storm formation. Although the Atlantic Niña has yet to be officially classified, which requires three months of sustained cooling, early signs suggest it may be having an effect.

Click on the image at right for a Cooperative Institute for Meteorological Satellite Studies (University of Wisconsin) graphic showing the location of the possible Atlantic Niña.

Part of the subtropical warming stems from the recent conclusion of an La Niña event. Climate change is also playing a role, with the 11 warmest Mays for subtropical ocean temperatures all occurring since 2015. While warmer oceans globally can sometimes fuel more intense hurricanes, long-term research suggests that the number of tropical storms may actually decline; however, the ones that form grow stronger and produce heavier rainfall.

Despite the slow start, forecasters caution that coastal residents should not lower their guard. Conflicting signals remain, with a significant warming trend across the Gulf of Mexico (designated as the Gulf of America by the Trump administration) and the potential return of La Niña later this season (there is a 38% risk between August and October), both of which could fuel tropical development later in the season.

Even in a quiet hurricane season, it only takes one storm making landfall to turn an otherwise calm year into a devastating one.

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