Tropical-force winds could arrive in South Florida as early as Friday night if the region gets hit by the system expected to form Tropical Storm Isaias.
Uncertainty is unusually high because the storm still lacks a well-defined center, said Robert Molleda, warning coordination meteorologist for the National Weather Service in Miami.
South Florida’s chances for experiencing tropical-force winds, which means speeds of at least 39 mph, stand at 20% to 30%, he said during a briefing Tuesday afternoon. Although the winds could arrive as early as Friday night, he said, they are more likely to hit Saturday.
Other unknowns are whether the storm will pass over much land in its course over the Caribbean and the potential storm-weakening impact of a layer of dry air between the storm and Florida.
An Air Force Reserve reconnaissance plane was flying through the system Tuesday afternoon to gather information.
For the first time this hurricane season, South Florida is in the cone.
The storm had a top wind speed of 40 mph, above the threshold for a tropical storm designation, according to a 5 p.m. update from the National Hurricane Center. But it still lacked the structure of a tropical cyclone, in which winds rotate around a low-pressure center. The disturbance has been designated Potential Tropical Cyclone Nine.
It’s still early in the forecast, so that could change for better or worse as the forecast evolves over the coming days.
“It cannot be stressed enough that since the system is still in the formative stage, greater than average uncertainty exists regarding both the short-term and longer-term track and intensity forecasts,” wrote Senior Hurricane Specialist Daniel Brown wrote in a forecast discussion describing the meteorological conditions of the storm.
The storm is so far expected to remain a tropical storm as it moves on a northwest path across the Leeward Islands of the northeastern Caribbean and over or close to the U.S. Virgin Islands and Puerto Rico, Hispaniola (the island that comprises the Dominican Republic and Haiti) and the Bahamas before closing in on Florida.
“Regardless of the exact track, the system is expected to bring locally heavy rainfall to much of the Lesser Antilles, and tropical-storm-force winds to portions of the Leeward Islands, the Virgin Islands, and Puerto Rico within the next 24-48 hours. After that time, a general west-northwestward heading should continue but as mentioned before, uncertainty exists as to how close the system tracks to Hispaniola, Cuba, the Bahamas, and Florida,” Brown wrote.
Isaias would be the ninth named storm of the already busy 2020 Atlantic hurricane season.
The disturbance was about 435 miles east of the eastern rim of the Caribbean area as of Tuesday morning. The system was packing maximum sustained winds of 40 mph and was moving toward the west at a decent clip of 23 mph.
Numerous Caribbean islands were under tropical storm warnings and watches. Tropical Storm warnings, which in this context mean tropical storm-force conditions are expected within 36 hours, were in place for Puerto Rico, the U.S. Virgin Islands and the northern coast of the Dominican Republic, among other islands.
There have been four other tropical storms so far this month: Edouard, Fay, Gonzalo and Hanna. Other named storms this year have included Arthur, Bertha, Cristobal and Dolly. Tropical Storm Arthur formed in mid-May, making this the sixth straight year that a named storm formed before the official start of hurricane season on June 1.
Virtually all estimates for this hurricane season predict an above-average number of storms, due to unusually warm ocean temperatures and global climate factors that are likely to reduce the high-altitude winds that can prevent the formation of hurricanes. On July 8, Colorado State University issued a slightly more pessimistic outlook for hurricane season than its earlier forecast, upping the number of named storms from 19 to 20.
For this week, the weather forecast calls for heavy thunderstorms in South Florida, according to the National Weather Service. Temperatures will range from a low of about 78 degrees to highs of about 90.
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