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Heavy rains hit Florida coast; Jova and Irwin a threat to Mexico

By: Dr. Jeff Masters, 1:01 PM GMT on October 08, 2011

A large low pressure system with heavy rain is developing this morning over Cuba, South Florida, and the Bahamas. The counter-clockwise flow around this low is bringing strong winds and heavy rains to much of the Florida coast. Radar-estimated rainfall amounts are already in excess of four inches along a stretch of Florida coast from West Palm Beach to Daytona Beach. Much of the region, including Cocoa Beach, is under a flood watch, high surf advisories, and a high wind watch for wind gusts of 45 - 55 mph. These these conditions will spread northwards to Georgia by Sunday, and South Carolina by Monday. I doubt that this storm will acquire enough organization to evolve into a subtropical storm that gets a name, based on the latest model output, and the fact that the storm's center may well be over the state of Florida. NHC is currently giving this storm a 20% chance of becoming a named tropical or subtropical storm by Monday morning. This is a large, diffuse system that will bring strong winds and heavy rains to a large area of the Southeast U.S. coast, regardless of the exact center location. Since the storm is going to get its start as a cold-cored upper-level low pressure system with some dry air aloft, it will not be able to intensify quickly.

Figure 1. Radar-estimated rainfall from the Melbourne, Florida radar as of Saturday morning.

Figure 2. Rainfall forecast for the 5-day period ending at 8 am EDT Thursday, October 12, 2011. The storm system affecting Florida this weekend is expected to bring up to 7 inches of rain along the coast. Heavy rains associated with a strong trough of low pressure are also expected to dump 4 - 6 inches of rain over drought-stricken areas of Texas, Oklahoma, and Kansas. Image credit: NOAA/HPC.

Heavy rain event coming for drought-stricken regions of Texas, Oklahoma, and Kansas
A strong low pressure system is expected to track across the Texas and Oklahoma Panhandles this weekend, bringing the heaviest rains of the year to drought-stricken portions of Oklahoma, Kansas, and Texas, including Abilene, where a flash flood watch is posted today. Rainfall in this region has been 13 - 20 inches below normal for the year; Lubbock, Texas has had just 3 inches of rain this year, compared to a normal of 16 inches. Rainfall amount of 1 - 4 inches will be common in the region over the weekend, and may be able to reduce drought conditions from the highest level (exceptional) to the second highest level (extreme.) However, the heaviest rains will stay confined to the western half of Texas, and Texas's major cities such as Houston will see very little rain over the weekend.

Figure 3. Visible satellite image of Hurricane Irwin and Tropical Storm Jova yesterday afternoon over the East Pacific.

Jova and Irwin: trouble for Mexico's Eastern Pacific coast
In the Eastern Pacific off the coast of Mexico, Tropical Storm Jova continues to slowly intensify. Jova will turn north and then northeast over the weekend as a strong trough of low pressure dives southward over northern Mexico. The computer models have come into better agreement on the track of Jova, with the region of coast centered on Manzanillo at greatest risk of a strike. Jova is under light wind shear of 5 - 10 knots, and shear is predicted to stay in the low to moderate range between now and landfall. Ocean temperatures are warm, 28 - 29°C, but the warm waters do not extend to great depth, limiting Jova's potential for rapid intensification. The upper atmosphere is also not cold enough to give Jova the kind of instability typically needed for rapid intensification. Nonetheless, both the GFDL and HWRF models predict Jova will intensify into a major Category 3 hurricane before landfall on Tuesday on the Mexican coast. The official NHC forecast is less aggressive, bringing Jova to Category 2 strength, which is probably reasonable, given the uncertainties regarding the possible interference from Hurricane Irwin to its west, and the fact that several other of our intensity models show very little strengthening. Regardless of Jova's strength at landfall, the storm will bring very heavy rains to the Mexican coast capable of causing dangerous flash floods and mudslides, beginning on Monday.

Once Jova has made landfall, Mexico needs to concern itself with Hurricane Irwin, farther to the west. Irwin will also be turned north and then northeast towards the coast of Mexico this weekend by the same trough of low pressure expected to affect Jova. The longer range computer forecast models show Irwin could make landfall as a hurricane on the Mexican coast late next week, along the same stretch of coast Jova will affect. If this verifies, the one-two punch of heavy rains from two tropical cyclones within a week could cause a devastating flood situation along the Mexican coast. However, the track forecast for Irwin has a higher degree of uncertainty than usual, and Baja is also at risk from this storm.

Jeff Masters


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