A tropical storm moved toward the Gulf of Mexico over southeastern Cuba on Friday afternoon and was expected to make landfall in western Florida on Sunday or Monday, with tropical storm warning flags flying for parts of Florida's west coast. At 11 a.m. ET on Friday, the National Hurricane Center (NHC) named the disturbance Potential Tropical Cyclone No. 4 (PTC 4), formerly known as Invest 97L. The PTC designation is used for a system that can bring a tropical storm or hurricane to a land area within 48 hours but has not yet formed a tropical cyclone.
PTC 4 slowly becomes more organized
At 11 a.m. EDT on Friday, PTC 4 was located 420 miles southeast of Key West, Florida, moving west-northwest at 16 mph with maximum sustained winds of 30 mph and a central pressure of 1,012 MB. watt. Satellite images show that this disturbance has a large area of severe thunderstorms with moderate rotation and is slowly becoming more organized. Dry air disrupts tissue, as does the high mountains across Cuba. Other conditions were also favorable for development, with ocean temperatures near a record 29.5 degrees Celsius (85°F) and wind shear speeds of 5-10 knots.
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PTC 4's route over the next week or more will be determined by three systems, all to its north:
- A powerful ridge of high pressure across the western and central United States
- Strong ridge in the Atlantic Ocean associated with the Azores-Bermuda High
- Weaknesses in between (low pressure trough)
Initially, PTC 4 will be guided primarily by the Atlantic Ridge, which pushes the system west-northwest along the length of Cuba on Friday. Along this route, PTC 4 will encounter increasingly humid conditions, with humidity expected to climb from 55% Friday morning to 65% Saturday night. Wind shear should remain light to moderate through the weekend and land interactions with the islands will decrease as PTC 4 moves into the open southeastern bay on Saturday. These conditions will allow PTC 4 to become Tropical Storm Debbie on Saturday night.
The models have agreed that an upper-level trough approaching the U.S. East Coast this weekend will turn PTC 4 northwest on Friday night or Saturday morning and then northward on Sunday, leading to landfall along the west coast of Florida or over the greater area. Day or Monday bend area. Currently, few models support PTC 4 becoming a hurricane because the storm has a relatively large circulation, needs time to consolidate, and does not have much time on the water before making landfall. At 11 a.m. ET on Friday, the NHC's official forecast said PTC 4 would peak as a severe tropical storm with 65 mph winds before making landfall Sunday night.
Florida faces heavy rain threat
Steering currents are likely to weaken on Sunday and Monday, with PTC 4 expected to slow to 5-10 mph from its current forward speed of 15 mph. This slow forward motion will give PTC 4 enough time to dump heavy rains, with freshwater flooding likely to be the storm's main threat. Record-warm sea surface temperatures in the eastern Gulf of Mexico will provide plenty of moisture for heavy rain: 4 to 8 inches of rain could fall on parts of Florida's west coast, with isolated amounts of up to 12 inches.
Long-term forecast for PTC 4
The most likely long-range fate of PTC 4 is to emerge over the Atlantic Ocean early next week off the northeastern coast of Florida, then move northeast along the southeastern United States coast and out to sea. As the week unfolds, heavy rain, high seas, and other impacts are possible along the eastern Georgia and Carolina coasts, depending on how far offshore (or inland) PTC 4 is and how fast it moves. The storm could also pose a threat to Canada's coastal provinces later this week.
GFS and a handful of members of the European modeling team suggest that the trough pulling PTC 4 to the northeast may not be strong enough to do the job, causing PTC 4 to become stuck in an area of weak steering current off the southeastern U.S. coast. In this case, PTC 4 could subject the coast to prolonged periods of heavy rain, with the potential for severe flooding impacts.
In the Tropical Weather Outlook issued at 8 a.m. ET on Friday, the National Hurricane Center projects that PTC 4 has at least a 70% chance of becoming a tropical depression by Sunday and a 90% chance by next Friday. . The first hurricane search flight to the center of PTC 4 is scheduled for Saturday afternoon, but NOAA aircraft will be tasked with sampling the environment around the storm Friday afternoon to improve model forecasts.
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