Ida strengthens, could be a hurricane for the Yucatan
Tropical Storm Ida is slowly strengthening, as it heads north-northwest towards an encounter with Mexico's Yucatan Peninsula. Infrared satellite loops show that Ida's heavy thunderstorms are expanding in area, and the cloud tops are cooling, indicating that the updrafts in the storm are growing stronger and pushing higher into the atmosphere. Wind shear is a moderate 15 - 20 knots, and is forecast to remain moderate through Sunday night. SSTs are a warm 29°C, and the total ocean heat content is over 100 kJ/cm^2, which is very favorable for intensification. The rains have ended over Nicaragua and Honduras, and Ida dumped up to eleven inches of rain along the coast in Nicaragua, causing flooding that damaged thousands of homes, but caused no deaths or injuries as of yet.
Figure 1. Satellite-estimated rainfall from Ida. The dark red colors (275 mm) represent rainfall in excess of about eleven inches. Image credit: NASA/TRMM project. Wunderground meteorologist Dr. Rob Carver presents another estimate of Ida's precipitation in his blog today.
The forecast for Ida
The moderate wind shear of 15 - 20 knots should allow for continued slow but steady intensification of Ida through Sunday afternoon, as long as the center remains over water. I give Ida a medium (30 - 50% chance) of reaching Category 1 hurricane strength before arriving at the Yucatan, since the total heat content of the ocean in the Western Caribbean is so high. We'll have a better idea of Ida's current strength early this afternoon, when the Hurricane Hunters have had time to investigate the storm.
The current wind speed probabilities for Cozumel give the Mexican resort island a 46% chance of receiving tropical storm-force winds of 39 mph of higher, Sunday or Monday. The odds of receiving hurricane force winds are given as 3%. Given the current trend in organization of Ida, these numbers should probably be bumped up to about 60% and 5%, respectively.
Once Ida crosses into the Gulf of Mexico on Sunday night, the storm will encounter much cooler SSTs and a strong trough of low pressure that will dump cold air into the storm and bring 40 knots of wind shear. This will cause Ida to lose its tropical characteristics and become a powerful extratropical storm with 45 - 55 mph winds. It is highly unlikely that Ida will hit the U.S. as a tropical storm, but it could still bring tropical storm-force winds of 45 mph to the coast next week as an extratropical storm.
I'll have an update later today, or on Sunday morning.