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Tropical Storm Fred Forecast Discussion Number 30

2021-08-17 04:48:24| National Hurricane Center (Atlantic)

Issued at 1000 PM CDT Mon Aug 16 2021 778 WTNT41 KNHC 170248 TCDAT1 Tropical Storm Fred Discussion Number 30 NWS National Hurricane Center Miami FL AL062021 1000 PM CDT Mon Aug 16 2021 The center of Fred has continued to move inland across the Florida Panhandle this evening, and is now located over extreme southeastern Alabama. Doppler velocities from NWS Doppler radars have gradually decreased and that data, along with recent surface observations, indicate that Fred is now a 35-kt tropical storm. Weakening should continue over the next several hours and Fred is expected to weaken to a tropical depression overnight. Additional weakening will occur on Tuesday while the circulation moves inland over Georgia and into the southern Appalachians. The global model guidance indicates that Fred's circulation will open into a trough of low pressure on Wednesday near the central Appalachians. Fred is moving north-northeastward or 015/10 kt. There is no change to the track forecast philosophy from the previous advisory. The cyclone should move north-northeastward at a faster forward speed between a mid-tropospheric ridge over the western Atlantic and a weak mid-level trough over the east-central United States. The new NHC track forecast is lies near the middle of the tightly packed dynamical model guidance. Although Fred is weakening, it is expected to bring flooding rains to portions of the southeastern and eastern United States during the next couple of days. KEY MESSAGES: 1. Through Tuesday, heavy rainfall may lead to considerable flash, urban, small stream, and isolated river flooding impacts across portions of the Florida Panhandle, southeastern Alabama, and from western Georgia into the southern Appalachians. By the middle of the week, Fred or its remnants will lift northward and impact the central Appalachians and Mid-Atlantic. Landslides are possible across the mountains of North Carolina and Blue Ridge Escarpment on Tuesday. 2. Tropical-storm-force winds, primarily in gusts, will continue over inland sections of the eastern Florida Panhandle, southeastern Alabama, and southwestern Georgia during the next few hours. FORECAST POSITIONS AND MAX WINDS INIT 17/0300Z 31.2N 85.2W 35 KT 40 MPH...INLAND 12H 17/1200Z 32.9N 84.8W 30 KT 35 MPH...INLAND 24H 18/0000Z 35.5N 83.6W 25 KT 30 MPH...POST-TROP/INLAND 36H 18/1200Z 38.5N 81.4W 20 KT 25 MPH...POST-TROP/INLAND 48H 19/0000Z...DISSIPATED $$ Forecaster Brown

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Tropical Depression Grace Forecast Discussion Number 15

2021-08-17 04:44:52| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Mon Aug 16 2021 000 WTNT42 KNHC 170244 TCDAT2 Tropical Depression Grace Discussion Number 15 NWS National Hurricane Center Miami FL AL072021 1100 PM EDT Mon Aug 16 2021 IR and microwave imagery during the past few hours indicate that Grace's convective organization has improved a little since this afternoon. However, it is currently unknown if that has translated to a better-defined surface wind field. Dvorak intensity estimates from TAFB and SAB at 00Z supported tropical storm strength, and it is possible Grace has redeveloped sustained winds of that magnitude. A hurricane hunter aircraft is scheduled to investigate Grace in a few hours, so it seems prudent to avoid making a big change before the plane gets there. Grace is therefore conservatively maintained as a 30 kt depression for this advisory. Regardless of Grace's exact intensity right now, the immediate threat is still torrential rainfall across Hispaniola overnight, which will likely cause severe flooding in some locations. The initial motion estimate is 280/12 kt. Confidence in the track forecast has increased considerably during the past 24 h and the track model spread is low. A mid-level ridge is forecast to build over the Gulf of Mexico during the next several days, which should keep Grace on a generally westward or west-northwestward track through day 5. Once Grace moves away from Haiti, it should remain over water until it reaches the Yucatan peninsula late Wednesday or early Thursday. Very little change was made to the official track forecast, which is based primarily on the multi-model consensus TVCN. Now that Grace is forecast to avoid all major land masses for the next couple of days, all of the intensity guidance calls for some strengthening to occur. That said, with the exception of the COAMPS-TC model, the intensity guidance as a whole shows a slower rate of strengthening than it did 6 h ago. The NHC forecast is now very near the IVCN intensity consensus throughout the forecast, including over the Gulf of Mexico where it continues to show Grace reaching hurricane strength. Despite the slightly lower guidance for this forecast, it still can not be ruled out that Grace will reach hurricane strength over the western Caribbean. When the hurricane hunter aircraft reaches Grace in a couple hours and provides more information about the current organization of cyclone, we should have a better feel for how quickly it could intensify prior to reaching the coast of Mexico. Key Messages: 1. Heavy rainfall across the Dominican Republic, Haiti, Cuba, Jamaica, the Cayman Islands, and the northern Yucatan Peninsula may lead to flash, urban, and small stream flooding, with the potential for mudslides highest in Haiti and the Dominican Republic. 2. Tropical storm conditions are possible over portions of Hispaniola overnight, and over Jamaica on Tuesday. Tropical storm conditions are expected over portions of the southern coast of Cuba on Tuesday, spreading westward to the Cayman Islands and possibly other portions of the southern coast of Cuba Tuesday evening through Wednesday morning. 3. There is a increasing risk of wind, rainfall, and storm surge impacts on the Yucatan Peninsula of Mexico Wednesday night and Thursday. Interests there areas should monitor the progress of Grace and updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 17/0300Z 18.2N 73.8W 30 KT 35 MPH 12H 17/1200Z 18.6N 75.7W 35 KT 40 MPH 24H 18/0000Z 19.1N 78.8W 40 KT 45 MPH 36H 18/1200Z 19.7N 82.0W 45 KT 50 MPH 48H 19/0000Z 20.3N 85.1W 50 KT 60 MPH 60H 19/1200Z 21.0N 88.2W 50 KT 60 MPH...INLAND 72H 20/0000Z 21.6N 91.3W 55 KT 65 MPH...OVER WATER 96H 21/0000Z 22.2N 95.9W 65 KT 75 MPH 120H 22/0000Z 22.5N 100.0W 40 KT 45 MPH...INLAND $$ Forecaster Zelinsky

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Tropical Storm Henri Forecast Discussion Number 5

2021-08-17 04:41:46| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Mon Aug 16 2021 000 WTNT43 KNHC 170241 TCDAT3 Tropical Storm Henri Discussion Number 5 NWS National Hurricane Center Miami FL AL082021 1100 PM AST Mon Aug 16 2021 Bursts of deep convection continue to pulse over the southeastern portion of Henri's circulation. Although the tropical cyclone is still being affected by dry-air entrainment and light-to-moderate shear, the latest subjective and objective satellite intensity estimates are a little higher than before, and a blend of those estimates yields an initial wind speed of 40 kt for this advisory. Henri is forecast to remain over SSTs of 28-29C throughout the forecast period, but the mid-level relative humidity is forecast to remain fairly dry, which is likely to only support gradual strengthening over the next day or so. After that time, a significant increase in northeasterly shear is anticipated, and that is likely to stop further strengthening. As mentioned in the previous advisory, given the small size of Henri, the tropical cyclone is likely to be more susceptible to this shear and it is possible that Henri weakens more than indicated below by day 3. The NHC intensity forecast is a blend of the various statistical aids, and the CTCI and HMNI models. Less weight is again placed on the HWRF model, which remains quite aggressive in strengthening Henri over the next several days despite the expected increase in shear and dry mid-level environment. Henri is moving southwestward or 215/4 kt. The tropical storm is forecast to move in a counterclockwise motion over the next several days as it moves around a mid-tropospheric high that is forecast to shift eastward over the western Atlantic. This motion should take Henri south of Bermuda late Tuesday or Tuesday night. By 72 hours, the storm is expected to reach the western extent of the ridge and turn northward, and then northeastward by the end of the forecast period. There is still some spread in the guidance as to when and how sharp the turn will be. As a result, the NHC track forecast is a blend of the typically reliable GFS and ECMWF models later in the period. FORECAST POSITIONS AND MAX WINDS INIT 17/0300Z 30.7N 63.3W 40 KT 45 MPH 12H 17/1200Z 30.5N 63.8W 45 KT 50 MPH 24H 18/0000Z 30.4N 64.8W 50 KT 60 MPH 36H 18/1200Z 30.3N 66.2W 50 KT 60 MPH 48H 19/0000Z 30.3N 67.8W 50 KT 60 MPH 60H 19/1200Z 30.5N 69.3W 50 KT 60 MPH 72H 20/0000Z 31.3N 70.1W 45 KT 50 MPH 96H 21/0000Z 32.8N 69.7W 45 KT 50 MPH 120H 22/0000Z 35.0N 66.5W 45 KT 50 MPH $$ Forecaster Brown

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