Tropical Depression 19 forms east of South Florida, tropical storm watch issued (Reports)
Tropical Depression 19 forms east of South Florida, tropical storm watch issued (Reports)

Surface observations on Friday indicate that pressures were falling over the northwestern and central Bahamas in association with an area of disturbed weather, designated 96L by the National Hurricane Center (NHC). Satellite images showed a steady increase in the organization and intensity of 96L’s heavy thunderstorm activity, with low-level spiral banding taking shape. Upper-level cirrus cloud motions indicated that upper-level outflow was occurring to the north, east, and south, and beginning to occur to the west – a sign that 96L was growing more organized.

This system is forecast to move westward at about 10 mph, crossing the Bahamas and Florida on Friday and moving into the eastern Gulf of Mexico on Saturday. By Sunday, steering currents will favor more of a west-northwest to northwest motion, which would bring 96L ashore between the central Louisiana and Florida Panhandle coasts on Tuesday.

The disturbance could become a tropical depression while it is near South Florida Friday night, but it is more likely to become a tropical depression on Saturday or Sunday, since it has to overcome its initial lack of spin.

Conditions for development Sunday through Tuesday are favorable in the Gulf of Mexico, with wind shear predicted to be a low 5 – 10 knots, sea surface temperatures a very warm 30 degrees Celsius (86°F), and the atmosphere reasonably moist, with a mid-level relative humidity of 60 – 65%. The system had weak model support for development on Friday morning, but this is the type of system that models struggle with in the early development stages.

Regardless of development, 96L will produce locally heavy rainfall over portions of the Bahamas, South Florida, and the Florida Keys through the weekend. In a special 11:25 a.m. EDT Friday Tropical Weather Outlook, NHC gave this system two-day and five-day odds of development of 60% and 70%, respectively. An Air Force hurricane hunter aircraft is scheduled to investigate 96L on Saturday afternoon.

Paulette a significant threat to Bermuda

In the central Atlantic, Tropical Storm Paulette, with 65 mph winds at 11 a.m. EDT Friday, was headed northwest at 10 mph toward Bermuda. Paulette was holding its own against very high wind shear of 40 knots from an upper-level trough of low pressure. That very high wind shear is expected to continue through Saturday morning, which should keep Paulette from strengthening.

By Saturday afternoon, the trough is predicted to split as Paulette penetrates through it, and wind shear will relax to a moderate 10 – 20 knots. Shear is predicted to fall to less than 10 knots on Sunday and Monday. The lower shear, combined with a moist atmosphere and warm sea surface temperatures near 29 degrees Celsius (84°F), will likely allow Paulette to strengthen into a hurricane. The majority of the top intensity models and the official NHC forecast call for Paulette to be a category 2 hurricane on Monday, when it will make its closest approach to Bermuda. The 6Z Friday run of the HWRF model predicted that Paulette would make a direct hit on the island on Monday morning as a category 3 hurricane with 120 mph winds.

Bermuda currently appears to be the only land area facing a possible Paulette landfall. Steering currents are well-positioned to turn Paulette to the north and then northeast on Monday and Tuesday, and the storm is not expected to be a landfall threat in the U.S. The first hurricane hunter mission into Paulette is scheduled for Saturday evening.

Rene not a threat to land

In the eastern Atlantic, Tropical Storm Rene, a low-end tropical storm with 40 mph winds at 11 a.m. EDT Friday, was headed west-northwest at 13 mph into the central Atlantic, far from any land areas. With adequately warm waters near 26.5 degrees Celsius (80°F), light to moderate wind shear, but a dry atmosphere, conditions appear marginally favorable for Rene to intensify to 60 mph winds by Sunday, as stated in the official NHC forecast. Rene is expected to turn more to the west by Monday and begin weakening; the storm is unlikely to affect any land areas.

According to floodlist.com, the tropical wave that became Rene produced torrential rains and deadly flooding in West Africa. Six flood deaths occurred in Senegal, with up to eight inches of rain falling in 24 hours on September 5. Three flood deaths occurred in Burkina Faso.

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