As of this 11 a.m this morning, the National Hurricane Center (NHC) says that Invest 99L has turned into Tropical Depression 9 (TD9). Satellite imagery now shows circulation in the area of low pressure over the west-central Caribbean which I posted about yesterday. Cuba and the Caymans have already issued tropical-storm warnings. Extremely heavy rainfall is expected there. And the storm should strengthen into a hurricane by Sunday. Yet the effects on the Houston region will like be felt offshore and in coastal areas.
TD9 Current Intensity and Location
The initial intensity of TD9 as of 11 a.m. Houston time is approximately 35 mph with gusts to 40. An Air Force Reserve reconnaissance aircraft is scheduled to be in the system later this afternoon to provide more information on the system’s structure and intensity.
TD9, now located just south of Grand Cayman, is moving northwestward at 13 mph. The National Hurricane Center (NHC) indicates the system should move steadily northwestward. That would bring the center near or over western Cuba late Friday, over the southeastern Gulf of Mexico on Saturday, and approaching the US Central Gulf coast on Sunday.
Models are in relatively good agreement regarding the track forecast for TD9. However, error at Day 4 is around 175 miles, so don’t focus on details of the long-range track forecast. Some shifts in the track are likely until the system consolidates and becomes better defined, according to the NHC.
TD9 will move over warm waters of the northwestern Caribbean during the next 24-36 hours. This, in combination with low vertical wind shear and a moist environment, should allow for steady strengthening.
Rapid Intensification Likely in Next 48 to 72 Hours
NHC forecasts TD9 to become a tropical storm later today or tonight. It could approach hurricane strength as it passes western Cuba.
Once the system moves into the Gulf of Mexico, conditions support additional strengthening. The NHC forecast explicitly shows rapid intensification between 48 and 72 hours for now.
Most global models show significant intensification of TD9 over the Gulf of Mexico. As a result, there is higher-than-normal confidence that a strengthening tropical cyclone will be moving over the Gulf this weekend.
1. Tropical storm conditions are likely in the Cayman Islands tonight and western Cuba Friday, with dangerous storm surge possible in western Cuba.
2. The system will likely produce life-threatening heavy rains, flash flooding and mudslides across Jamaica, the Cayman Islands, western Cuba, and portions of the Yucatan Peninsula.
3. This system should approach the northern Gulf Coast at or near major hurricane intensity on Sunday, although the forecast uncertainty is larger than usual since the system is just forming. There is a risk of life-threatening storm surge, damaging hurricane-force winds, and heavy rainfall Sunday and Monday along the northern Gulf Coast from the Florida Panhandle to the upper Texas coast, with the greatest risk along the coast of Louisiana. Interests in these areas should closely monitor the progress of this system and ensure they have their hurricane plan in place.
Likely Hazards in Islands and Mainland
The main hazards associated with TD9 as it passes Cuba and the Caymans will be:
2 to 4 feet above normal tide levels in areas with onshore flow. Near the coast, the surge will be accompanied by large and destructive waves.
Tropical storm conditions are expected in the Cayman Islands tonight and Cuba on Friday.
The depression is expected to produce total rainfall accumulations of 6 to 10 inches with maximum totals of 15 inches across Jamaica. Rainfall totals of 8 to 12 inches with isolated maximum amounts of 20 inches are expected across the Cayman Islands, western Cuba, and the northeast Yucatan Peninsula. These rainfall amounts may produce life-threatening flash floods and mudslides. Rainfall from this system is likely to begin impacting portions of the central U.S. Gulf Coast by early Sunday.
Swells generated by this system will begin affecting Jamaica, the Cayman Islands and Cuba tonight and Friday. These swells are likely to cause life-threatening surf and rip current conditions.
Lindner Cautiously Optimistic At This Point
Jeff Lindner, Harris County meteorologist believes, “Impacts along the upper TX coast will likely be increasing swells and minor coastal flooding at high tide late this weekend into early next week.”
Monitor forecasts closely in case things change and be prepared for anything. We still won’t reach the peak of hurricane season until mid-September.
Posted by Bob Rehak at noon on 8/26/2021 based on information from NHC and HCFCD
1458 Days after Hurricane Harvey