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Tropical Storm Fred Forecast Discussion Number 9
2021-08-11 22:40:25| National Hurricane Center (Atlantic)
Issued at 500 PM EDT Wed Aug 11 2021 000 WTNT41 KNHC 112040 TCDAT1 Tropical Storm Fred Discussion Number 9 NWS National Hurricane Center Miami FL AL062021 500 PM EDT Wed Aug 11 2021 During the past several hours, the center of Fred has moved inland over the Dominican Republic. The storm continues to produce an area of convection near and southeast of the center. However, the low-level circulation is losing some organization as it passes over mountainous terrain. There have been no observations near the center recently, so the initial intensity of 35 kt is based mainly on weakening from the previous over water intensity. The initial motion is a somewhat uncertain 290/13. Some erratic motion is expected during the next 12 h or so as the center moves over the mountains of Hispaniola. After reaching the water, the cyclone is expected to moves west-northwestward on the south side of the subtropical ridge through about 60 h. After that, a northwestward motion is expected through the end of the forecast period as Fred moves toward a weakness in the ridge. The track guidance becomes a bit divergent during this time, with the ECMWF, Canadian, and HWRF models showing a track near or over the Florida Peninsula, while the GFS, UKMET, and HMON models show the center passing south and west of the Florida Keys, followed by a more northward motion over the Gulf of Mexico. The new forecast track is between these extremes, and it has only minor adjustments from the previous NHC track. Fred is expected to weaken to a depression over Hispaniola during the next 12 h. Once back over water, the cyclone is expected to be in a moderate westerly shear environment through at least 60 h. Due to that, and the uncertainty in how well organized the system will be after crossing Hispaniola, the intensity forecast shows only modest intensification during this time. After that time, the global models forecast that an upper-level trough over Florida will gradually move to the north, with an large upper-level anticyclone following near or to the southeast of Fred. How close this anticyclone gets to Fred will determine how much the shear decreases while the system is over the eastern Gulf of Mexico, and the global models are not in great agreement on this. The GFS and Canadian keep the high far enough to the east to expose Fred to southwesterly upper-level winds, while the UKMET and ECMWF move it closer to the storm. The intensity forecast will show a slightly faster rate of strengthening after 72 h to match the guidance and the previous forecast. However, there is lower than normal confidence in this part of the intensity forecast. KEY MESSAGES: 1. Tropical storm conditions are ongoing across portions of the Dominican Republic. Tropical storm conditions are possible in northern Haiti and the southeastern Bahamas this evening, and in portions of Cuba by tonight. 2. Through early Thursday morning, heavy rainfall could lead to flash, urban, and small stream flooding, along with possible rapid river rises and potential mudslides in the Dominican Republic. 3. There is a risk of wind and rainfall impacts elsewhere in portions of Hispaniola, the Bahamas, and Cuba during the next few days, although the forecast is more uncertain than usual since Fred is forecast to interact with Hispaniola through tonight. 4. There is an increasing risk of wind and rainfall impacts in Florida beginning Friday night or early Saturday in the Keys and spreading northward through portions of the Peninsula and the Panhandle Saturday through Monday. Beginning Friday, heavy rainfall could lead to areal, urban, and small stream flooding, and possible rapid river rises across southern Florida. Interests throughout Florida should monitor Fred's progress and check updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 11/2100Z 18.9N 71.0W 35 KT 40 MPH...INLAND 12H 12/0600Z 19.8N 72.7W 30 KT 35 MPH...INLAND 24H 12/1800Z 20.9N 75.0W 30 KT 35 MPH...OVER WATER 36H 13/0600Z 21.9N 77.1W 35 KT 40 MPH 48H 13/1800Z 22.9N 79.2W 35 KT 40 MPH 60H 14/0600Z 23.9N 80.6W 40 KT 45 MPH 72H 14/1800Z 25.3N 82.0W 40 KT 45 MPH 96H 15/1800Z 28.5N 84.0W 50 KT 60 MPH 120H 16/1800Z 31.0N 85.0W 45 KT 50 MPH...INLAND $$ Forecaster Beven
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