May 27, 2025 Tuesday Tropical Update
A surge of moisture from the Lesser Antilles into the Caribbean reaches the Gulf of Mexico by Day 10. This pattern is conducive for tropical storm development into the second week of June.
Alvin parallels the coast of Mexico and decays prior to making landfall, most likely. The moisture is pulled into the U.S. Southwest to enhance rainfall chances over Southern California and Arizona, including Phoenix into early next week.
Large cloud-free dust haze has moved further in the Eastern Atlantic with a strong Saharan Air Layer (SAL). Tropical waves over Burkina Faso and Sudan are vigorous, and several days from emerging over the Atlantic. The Easterly Wave season is underway but we don’t expect development in the Main Development Region (MDR) of the tropical Atlantic until July.
SAL into Lesser Antilles will make the Gulf in 3-4 days. Then, the next major plume will be right on its heels. The dust inhibits solar radiation from reaching the ocean surface — net cooling!
Actual sea-surface temperatures < 26°C won’t support tropical storm genesis through normal convective pathways shutting off the MDR for a while. The Gulf and Caribbean are open for business with 28°C surface water available.
Anomaly (compared to 1991-2020) is 1-2°C above normal across the Gulf and into the Southwest Atlantic off the coast of Florida to Bermuda. However, even if it’s warmer than normal, the actual T is still < 26°C.
actual Sea-Surface Temperatures (SST) help form and intensify tropical storms and hurricanes NOT the anomaly. We need sustained 26°C SST for typical tropical pathway storm development. You can see the green (under 26°C) extends still to 10°N latitude = too chilly for typical MDR development, but that will warm over the next 2-weeks to be viable.
The Caribbean is already (always) warm enough for a major hurricane (28°C). The Gulf is still chilly across the northern half of the basin.
Two tropical waves — one heading through Venezuela = moderate convection, and another approaching the NE coast of South America with some convection.
However, no tropical development expected. But these systems can provide the seedlings for Eastern Pacific hurricanes in 10-14 days from their emergence off African coast.
Both ECMWF and GFS show a disturbance in the Caribbean or over Yucatan into the Gulf of Mexico by Day 8-10 suggestive of decent chance of a tropical storm. There is some ensemble support. Still quite a ways out over the skillful forecast horizon.
There are 10/51 (20%) or so that show a strong tropical storm or hurricane in the next 15-days into mid-June.
Invest 90E designated by NHC with 90% chance of tropical storm development in the next 48-hours.
Upper-level wind shear is not ideal with a cut-off low dipping off Southern California to help steer Invest 90E (Alvin) quickly to the north and then northeast over colder water into Mexico.
My favorite weather parameter shows Alvin over the next 5-days near the coast of Mexico.
Note the cooler equatorial waters under 26°C = green and below normal.
Intensity of Alvin?
HWRF is near major hurricane pressure and winds.
HAFS (A and B) are weaker, but still Category 1 hurricane. Makes more sense with upper-level conditions.
— additional development possible on the heels of Alvin in line with climatology of the Eastern Pacific. June is a rather busy month out there!
