96L satellite image
Visible satellite image of disturbance 96L at 12:10 p.m. EDT Friday, September 11, 2020. (Image credit: NOAA/RAMMB)

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.

Figure 1 96L
Figure 1. Radar image of 96L at 12 p.m. EDT September 11. The system was beginning to develop curved low-level spiral bands. (Image credit: Bahamas Department of Meteorology)

Forecast for 96L

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.

Figure 2
Figure 2. Predicted path of Atlantic tropical cyclones over the next seven days from the 0Z Friday, September 11, run of the European ensemble model. Most of the model’s 51 ensemble members (colored lines, which show minimum central pressure) predicted Paulette would come very close to Bermuda as a hurricane, then recurve to the northeast. Four other potential areas to watch include two disturbances in the Gulf of Mexico with 5-day formation odds of 20% and 30%, and two tropical waves moving off the coast of Africa with 5-day formation odds of 40% and 90%. The most concerning was a tropical wave that emerged from the coast of Africa on Friday (5-day formation odds of 90%), expected to move westward and potentially threaten the Lesser Antilles Islands in 6 – 8 days. (Image credit: weathermodels.com)

A Gulf of Mexico disturbance worth watching

NHC was monitoring an area of interest over the north-central Gulf of Mexico producing a few disorganized showers and thunderstorms on Friday afternoon. Some slow development is possible while this system moves westward and then southwestward over the northern and western Gulf of Mexico through Tuesday. Dry air over the western Gulf of Mexico is likely to inhibit its development. In an 11:25 a.m. EDT Friday Tropical Weather Outlook, NHC gave this system two-day and five-day odds of development of 10% and 30%, respectively.

95L off the coast of Africa a threat to develop

Top models for forecasting tropical cyclone genesis strongly support development of a tropical wave located on Friday afternoon a few hundred miles south of the Cabo Verde Islands, off the coast of Africa.

This system, designated 95L by NHC, is predicted to move mostly westward at low latitude at 15 to 20 mph. Given its lower-latitude position than that of Paulette and Rene, 95L may be a long-range concern for the Caribbean and North America, though most of the computer model forecasts with their Friday morning runs indicated a path north of the Caribbean. Over 20% of the 51 ensemble members from the 0Z Friday, September 11, run of the European ensemble forecast showed that this new system would be a named storm in the Caribbean by Thursday, September 17. The system could affect the Lesser Antilles Islands as early as Wednesday night.

The future track of 95L could be affected by the position and strength of Paulette and Rene, by the structure of the wave once it organizes into a tropical depression, and also by the path and intensity of another tropical wave moving off the coast of Africa on Friday – variables very difficult to accurately predict. In an 11:25 a.m. EDT Friday Tropical Weather Outlook, NHC gave 95L two-day and five-day odds of development of 70% and 90%, respectively.

PHOTOHow to protect your home from flood damage

A wave behind 95L, emerging from the coast of Africa on Friday afternoon, was given two-day and five-day odds of development of 10% and 40%, respectively. This wave will move west-northwest through the Cabo Verde Islands over the weekend.

The next two names on the Atlantic list of storms are Sally and Teddy.

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Posted on September 11, 2020 (2:07pm EDT).

Jeff Masters, Ph.D., worked as a hurricane scientist with the NOAA Hurricane Hunters from 1986-1990. After a near-fatal flight into category 5 Hurricane Hugo, he left the Hurricane Hunters to pursue a...

171 replies on “Tropical depression may form near Florida on Saturday; Tropical Storm Paulette a significant threat to Bermuda”

  1. Looking for a reason this won’t be a 2005 repeat? Gulf Eddies far different than 2005 when Hurricane Katrina took full advantage of a super heated eddy. In 2018 a similar eddy was in place as well. Hurricane Katrina like intensification should not happen without this enhancer. RI possible if not likely though, and T.S Sally will eventually be pushing a large storm surge. Sally is a big storm, some shear, no super eddy, some reasons to hope that keeps T.S Sally on the steady not explosive increase. https://www.aoml.noaa.gov/phod/dhos/fig_sat/gc//20200912_gc.gif

    1. Katrina was unique to why super rapid intensification took place. Sally does not have the conditions to bomb out to a category five. Just not there. A large 115-125 mph major is not out of the question for Sally’s peak. Updated shear map shows shear has increased which will tamper potential for R.I. Shear still conducive to intensification though, in the 10-15kt range. http://tropic.ssec.wisc.edu/real-time/atlantic/winds/wg8shr.GIF

  2. https://www.tropicaltidbits.com/sat/satlooper.php?region=17L&product=truecolor




    4 different simultaneous views of 4 different areas, 4 sets of twins, all paired up and ready to blow…2020 may not be an ACE master yet, but it is the year of dancing partners arriving for the big dance together. And, there are more out there in parts of the globe not shown. They are taking the year and conveying the double up to heart.

    And all 4 of those swirling pairs (dancing partners), are all close enough to be conjoined in some way with 1 another currently by some kind of cloud banding.

    I just hope anyone and everyone, possibly in potential harms way anywhere, is fully prepared, stay safe ya’ll.

      1. Duel disasters, one burning, one inbound, quite the picture. I can’t even imagine being in California right now. Thanks Terry for the overview.

      2. Water vapour is often discussed and recognized as being an important part of the global warming process. The water vapour feedback process is most likely responsible for a doubling of the greenhouse effect when compared to the addition of carbon dioxide on its own.

      3. Last weekend, there was barely a cloud visible across the CONUS (was 1 tiny spot of convection in southwestern TX I think)…What a difference a week makes. But there was smoke. Then the Alaska Snow/Low and the Tropics moved in.

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