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Major rains for Southeast U.S., TX, KS, and OK; Jova and Irwin a threat to Mexico

By: Dr. Jeff Masters, 2:24 PM GMT on October 07, 2011

A large low pressure system with heavy rain is expected to develop over Cuba, South Florida, and the Bahamas on Saturday. The counter-clockwise flow around this low will bring strong winds and heavy rains to much of the Florida coast on Saturday, and 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. This will be 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. Portions of the coastal waters along the Florida Panhandle, as well as from Northeast Florida to South Carolina, are likely to experience sustained winds of 30 - 40 mph Monday and Tuesday. 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. Rainfall forecast for the 5-day period ending at 8 am EDT Wednesday, October 12, 2011. The storm system affecting Florida this weekend is expected to bring up to 11 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. 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. As of yesterday, Houston had gone 253 consecutive days without a one-inch rainstorm, a new record. The longest previous such streak was 192 days, set in 1917 - 1918. The last one inch rainstorm in the city was January 24, 2011. Remarkably, the local National Weather Service office has not issued any flood products in over a year.

Figure 2. The amount of rain needed to break the Texas drought is in excess of 15 inches (purple colors) over most of the state. This year's drought is officially Texas' worst one-year drought on record. Image credit: NOAA/NWS.

Philippe being ripped up by wind shear
Hurricane Philippe, the fifth hurricane of the 2011 Atlantic hurricane season, doesn't have much time left as a hurricane, due to high wind shear of 40 - 50 knots that is starting to tear the storm apart. Satellite loops show Philippe has become lopsided and is now missing its eye. Philippe will continue to degrade in appearance over the next few days, and will die in the middle Atlantic without affecting any land areas.

Figure 3. True-color MODIS image of Philippe over the mid-Atlantic taken at 10:45 am EDT October 6, 2011. At the time, Philippe was a Category 1 hurricane with 80 mph winds. Image credit: NASA.

Jova and Irwin: double trouble for Mexico's Eastern Pacific coast
In the Eastern Pacific off the coast of Mexico, two new tropical storms spun up yesterday. The storm of greatest immediate concern is the one closest to the coast, Tropical Storm Jova. Jova is currently headed west-northwest, parallel to the coast, but 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 a fairly wide spread for the track of Jova, with the region of coast centered on Puerto Vallarta between Manzanillo and Tuxpan at greatest risk of a strike. Jova is under moderate shear of 10 - 20 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 Monday on the Mexican coast. The official NHC forecast is less aggressive, bringing Jova to Category 1 strength. This is probably too conservative, and I expect Jova will be at least a Cat 2 at landfall. One possible impediment to development may be Jova's close proximity to Hurricane Irwin to its west. Upper-level outflow from Irwin could weaken Jova, and the two storms may compete for the same moisture. The two storms are close enough to each other--about 650 miles apart--that they will affect each others' track, as well. Whenever two storms of at least tropical storm strength approach within 900 miles of each other, a phenomenon known as the Fujiwhara effect comes into play. This effect causes the two storms to rotate counterclockwise around a common center. Since the degree of rotation will depend on the relative strengths of the the two storms, and our ability to make good intensity forecasts is limited, the track forecasts for both Jova and Irwin will have a higher degree of uncertainty than usual. 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 Sunday night.

Once Jova has made landfall, Mexico needs to concern itself with Hurricane Irwin, which is gathering strength farther to the west. Irwin is also moving to the west-northwest, and 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.

Jeff Masters

Drought Hurricane

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.