Alma nears hurricane strength, takes aim at Nicaragua; major tornado outbreak today

Tropical Storm Alma, in the Eastern Pacific off the coast of Nicaragua, is steadily intensifying, and appears likely to develop into a hurricane later today. The latest QUikSCAT pass from 8:03am EDT showed winds of 50 knots (58 mph) near the center, and a recent microwave image (Figure 1) showed the formation of an eye. Alma is generating very heavy rains in excess of six inches per day near its center. So far, satellite estimates of rainfall (Figure 2) indicate that 3-6 inches of rain has fallen over portions of Costa Rica and Nicaragua, and rainfall will continue to increase in these nations through Saturday. All of Central America, except for Panama, is at risk of flash flooding that will create dangerous mud slides over the next three days, and Alma has the potential to be a major disaster for Central America. Nicaragua, in particular, is at high risk of experiencing flash flooding and mud slides capable of causing heavy loss of life, due to its high mountainous terrain that will receive up to 20 inches of rain. However, the mountainous regions along the Pacific coast of Costa Rica, Honduras, El Salvador, and Guatemala are also at high risk of destructive flooding and mud slides.


Figure 1. Microwave image (colored, left side) and visible satellite image (gray colors, right side) of Tropical Storm Alma taken at 10:14am EDT Thursday May 29, 2008. An eye is visible in the color microwave image, surrounded by intense echoes (red colors) of an eyewall on the west side of the eye. Microwave instruments carried on polar-orbiting satellites can only "see" a swatch of Earth's surface a few hundred kilometers in diameter, and the edge of this swath happened to fall very near the eye of Alma at this time. Image credit: Navy Research Lab, Monterey.

Since Alma now dominates the circulation pattern of the region, none of the computer models are predicting that a tropical depression will form in the Western Caribbean in the coming week. It is possible that Alma could cross Central America and pop out in the Gulf of Mexico's Bay of Campeche. However, the crossing of Central America will severely disrupt the storm, and the odds of Alma becoming a depression in the Atlantic basin are very low. I am not expecting moisture from the storm to reach the U.S. Satellite loops show that Alma has developed a large circulation that extends into the Western Caribbean, and rains from Alma will affect Jamaica, the Cayman Islands, Mexico's Yucatan Peninsula, and western Cuba through Saturday. These areas can expect heavy downpours with rainfall totals of 3-6 inches through Saturday. Rainfall may be heavier, perhaps 5-10 inches, in Belize and along the north coast of Honduras.


Figure 2. Observed precipitation for the 24 hours ending at 12Z (8am EDT) Thursday May 29, 2008. Rainfall amounts in excess of 150mm (six inches, green colors) occurred near the coast of Costa Rica. Image credit: U.S. Navy Monterey.

Major severe weather outbreak today in the Plains
The Storm Prediction Center is calling for a "High" risk of severe weather across Iowa and Nebraska this afternoon--the highest level of severe weather alert. Expect another significant tornado outbreak today in the Plains. The Weather Underground Severe Weather page and Tornado page are good places to go to follow the severe weather. Also, tune in to the chase accounts and awesome storm photos from Wunderblogger Mike Theiss. Mike is in Tornado Alley this week, performing his annual chase efforts.

I'll have an update Friday morning, or tonight if there's major tornado action to talk about.

Jeff Masters