Super Sunday tropical disturbance forms in Yucatan Channel

OK, this is officially nuts. The first Super Sunday Invest in history formed this morning in the Yucatan Channel between Mexico and Cuba, and is slowly becoming more organized as it moves northeast towards Southwest Florida. The new disturbance, dubbed Invest 90L by NHC late this morning, has a modest but growing area of heavy thunderstorms near its center. Visible satellite imagery shows a pronounced spin at middle levels of the atmosphere, and 90L may be able to close off a surface circulation if it can find 24 more hours of marginally favorable conditions. Radar loops out of La Bajada on the western tip of Cuba show heavy thunderstorms over Western Cuba, but there is no organization of the echoes into low-level spiral bands. Wind shear is a high 20 - 25 knots, which is marginal for tropical storm formation. Ocean temperatures in the Yucatan Channel are 26 - 26.5°C (79 - 80°F), which is also marginal. 90L is suffering from ingestion of dry air along its western flanks, courtesy of an upper-level trough over the Gulf of Mexico, as seen on water vapor satellite imagery.


Figure 1. Is this football season or baseball season? The Super Sunday Invest 90L looks more characteristic of something we'd expect to see in May.

Forecast for 90L
Both the GFS and ECMWF models predict that the shear will remain below 25 knots through Monday, so there is some potential for continued development of 90L as it moves northeast towards South Florida. On Monday afternoon or evening, the storm will merge with a cold front and move over South Florida, bringing heavy rains of 1 - 3 inches and sustained winds of 20 - 25 mph. If it develops into a tropical depression or tropical storm, which I put at a 20% chance, the winds and rains will be higher. I doubt 90L has enough time or favorable enough conditions to become a tropical or subtropical depression, especially considering the disturbance's small size. There is a historical precedent for a tropical storm this time of year in this location--the 1952 Groundhog's Day tropical storm that hit Southwest Florida. According to Wikipedia,

The 1952 Groundhog Day Storm was the only Atlantic tropical cyclone on record in the month of February. First observed in the western Caribbean Sea on February 2, it moved rapidly throughout its duration and struck southwestern Florida within 24 hours of forming. In the state, the winds damaged some crops and power lines, but no serious damage was reported.

Jeff Masters