The watching and waiting continues for Invest 99L as it rolls toward The Bahamas. 99L remained a very large but very disorganized tropical wave on Thursday afternoon. Visible satellite imagery shows one circulation near the extreme southeastern portion of the Bahamas and Turks and Caicos Islands. This circulation is largely naked, with little cloudiness around it, although some filling-in was evident late Thursday afternoon. Air Force Hurricane Hunters found winds of tropical-storm force in 99L early Thursday, but since the circulation was not fully closed, it could not yet be classified as a tropical depression or tropical storm. On their second mission of the day, Air Force Hurricane Hunters found that winds to the east of this not-quite-closed circulation had decreased by early afternoon Thursday to just below tropical storm force.
Well south of the storm-free circulation center of 99L, very intense thunderstorms were developing late Thursday afternoon along the north coast of Haiti and the Dominican Republic, while decreasing on the south side of the island. Most provinces of the Dominican Republic were on flood alert Thursday evening, and rivers were already surging according to an Associated Press report.
Based on the Thursday afternoon flight data, NHC’s Tropical Weather Outlook issued at 2:00 pm EDT Thursday reduced the odds that 99L will develop into at least a tropical depression to 40% by Saturday and 70% by Tuesday. The slow pace of development thus far isn’t a total shock, as a number of computer models suggested as far back as Monday night that 99L would be no more a mid-strength tropical storm at best by this point. However, the lack of development at this point will keep 99L from growing as intense as it otherwise might have been by this weekend.
Figure 1. Visible image of Invest 99L as of 2045Z (4:45 pm EDT) Thursday, August 25, 2016. Image credit: NOAA/NESDIS.
99L remains a potential threat for Florida and other Gulf Coast states...MORE
It’s too soon to completely write off 99L as a threat to Florida, as it still has at least 48 hours to organize before reaching the area. The wave remains a potentially significant threat to the Gulf of Mexico coast next week. Up to now, a substantial amount of vertical wind shear has helped to displace the upper- and lower-level portions of 99L, while also driving large amounts of dry air into the wave. The University of Wisconsin-CIMSS wind shear analysis from Thursday afternoon was still showing a high 25 knots of wind shear over the core of 99L, which likely accounts for the inability of the storm to develop any heavy thunderstorm activity at its center of circulation. This state of affairs may change in the near future, though. Wind shear as analyzed by the SHIPS model is forecast to fall below 15 knots by Friday afternoon and then to remain in the low to moderate range, 5 - 15 knots, through Tuesday.
Along with the reduced wind shear on Friday and Saturday, 99L will be traveling over very warm waters (around 30°C or 86°F). Since tropical waves often develop convection overnight, we’ll have to see if 99L can form a core of showers and thunderstorms around its low-level center during this usual noctural peak. If it does, the chances of a substantial tropical storm reaching Florida will rise significantly....
By not tracking over the Florida peninsula the storm has a better chance of sucking up energy from that warm Gulf water.