97L Growing More Organized in Western Caribbean

A tropical disturbance (Invest 97L) over the Western Caribbean is moving to the northwest at 10 mph and is generating heavy rains over Jamaica and the Cayman Islands. Kingston, Jamaica picked up 2.60" of rain on Monday. Satellite loops show that 97L has a modest area of heavy thunderstorms that have increased in intensity and organization Tuesday morning. The broad area of spin associated with 97L is growing more defined, and the storm is taking advantage of wind shear that has fallen to the low range, 5 - 10 knots, as well as an upper-air anticyclone that has set up over the storm, providing good ventilation aloft. Dry air covers the Northwest Caribbean, as seen on water vapor satellite loops, and this dry air is slowing development. Ocean temperatures are a very warm 29°C (84°F). A hurricane hunter flight scheduled for Tuesday afternoon was cancelled due to 97L's lack of organization, and has been rescheduled for Wednesday.


Figure 1. Latest satellite image of Invest 97L.

Forecast for 97L: development into at least a tropical depression likely
WInd shear is expected to remain low to moderate through Friday, according to the latest SHIPS model forecast. The lack of wind shear on Tuesday and Wednesday should allow 97L to moisten the atmosphere and wall off the dry air to its northwest that is slowing down development, and I expect 97L will be close to tropical depression status by Wednesday morning. By Wednesday night, 97L will cross the northeastern tip of Mexico's Yucatan Peninsula, bringing 4 - 8" of rain to the peninsula and to Western Cuba. Passage over the Yucatan will act to disrupt the storm. The atmosphere will grow drier and wind shear will increase as 97L moves northwards over the Gulf of Mexico on Thursday and Friday, and these combined effects will likely retard development. A trough of low pressure and an associated cold front will be moving through Louisiana on Saturday, and the associated upper-level westerly winds will be able to turn 97L more to the northeast as it approaches the coast on Friday. The GFS model predicts landfall will occur along the Florida Panhandle, while the European model is farther west, taking the storm over Eastern Louisiana. Neither model shows 97L developing tropical storm-force winds. In their 8 am EDT Tuesday Tropical Weather Outlook, NHC gave 97L 2-day odds of development of 30%, and 5-day odds of 50%. I give a 40% chance 97L will be Tropical Storm Karen with top winds of 40 - 60 mph at landfall between Louisiana and the Florida Panhandle on Friday night, a 10% chance it will be stronger, and a 50% chance it will be a tropical depression or mere tropical disturbance.


Figure 2. MODIS satellite image of Jerry, taken at 10:30 am EDT on October 1, 2013. Image credit: NASA.

Tropical Storm Jerry in the Central Atlantic no threat
Tropical Storm Jerry formed on Monday in the Central Atlantic, far from land. Jerry is the tenth named storm of the 2013 Atlantic hurricane season, and arrived twenty days before the usual appearance of the season's tenth named storm, which is October 19. Jerry is not a threat to any land areas.

Jeff Masters