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Tropical Storm Grace Forecast Discussion Number 16
2021-08-17 10:59:57| National Hurricane Center (Atlantic)
Issued at 500 AM EDT Tue Aug 17 2021 000 WTNT42 KNHC 170859 TCDAT2 Tropical Storm Grace Discussion Number 16 NWS National Hurricane Center Miami FL AL072021 500 AM EDT Tue Aug 17 2021 An Air Force Reserve reconnaissance aircraft had difficulty locating the center of Grace early this morning. The last few visible satellite images along with 0200Z ASCAT wind data indicated that a lee-side surface low had formed south of the western tip of Haiti. That feature has gradually been pulling northward closer to the deep convection that has developed near the well-defined mid-level circulation center. The initial position is the midpoint between the recon position in the latest vortex message and the mid-level circulation noted in passive microwave imagery. The aircraft also found some patches of 925-mb flight-level winds of 48-51 kt, which equates to surface winds of 36-38 kt. Reliable SFMR surface winds obtained by the aircraft were also in the 36-38-kt range. Based on these data, Grace was upgraded back to a 35-kt tropical storm at 0600 UTC. Regardless of Grace's exact intensity right now, the immediate threat is still torrential rainfall across western Hispaniola today and over Jamaica this afternoon and tonight, which will likely cause severe flooding in some locations. The initial motion estimate is an uncertain 280/14 kt. A strong mid-level ridge is forecast to build westward across Florida and the Gulf of Mexico during the next several days, which should keep Grace on a westward or west-northwestward track through the 120-h forecast period. Only a very sight southward shift in the previous forecast track was made, which was due primarily to the new estimated southerly initial position, and the new NHC forecast track lies along the northern edge of model guidance envelope. Once Grace passes Jamaica in 12-18 hours, the cyclone will be passing over water temperatures near 30 deg C and into a more divergent upper-level wind flow pattern. These two favorable conditions should allow for Grace to slowly intensify and possibly be near hurricane strength by the time the cyclone reaches the Yucatan peninsula in about 48 hours. Thereafter, Grace will weaken as it pass over Yucatan, and then re-strengthen some over the Bay of Campeche before reaching mainland Mexico in about 96 hours. The NHC intensity forecast is close to a blend of the HCCA and IVCN consensus models. 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 and over Jamaica on today. Tropical storm conditions are expected over portions of the southern coast of Cuba today, spreading westward to the Cayman Islands and possibly other portions of the southern coast of Cuba this 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 17/0900Z 18.2N 75.4W 35 KT 40 MPH 12H 17/1800Z 18.6N 77.6W 40 KT 45 MPH 24H 18/0600Z 19.1N 80.7W 45 KT 50 MPH 36H 18/1800Z 19.7N 83.9W 50 KT 60 MPH 48H 19/0600Z 20.4N 87.0W 60 KT 70 MPH 60H 19/1800Z 21.0N 90.0W 50 KT 60 MPH...INLAND 72H 20/0600Z 21.4N 92.7W 55 KT 65 MPH...OVER WATER 96H 21/0600Z 22.0N 97.2W 60 KT 70 MPH 120H 22/0600Z 22.3N 101.4W 30 KT 35 MPH...INLAND $$ Forecaster Stewart
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Tropical Depression Fred Forecast Discussion Number 31
2021-08-17 10:41:06| National Hurricane Center (Atlantic)
Issued at 400 AM CDT Tue Aug 17 2021 000 WTNT41 KNHC 170840 TCDAT1 Tropical Depression Fred Discussion Number 31 NWS National Hurricane Center Miami FL AL062021 400 AM CDT Tue Aug 17 2021 Fred has moved farther inland and is now located near the border of southwestern Georgia and southeastern Alabama. Between 0400-0600 UTC, Doppler radar data from Tallahassee, Florida, still showed 68-70 kt velocities between 9,000-10,000 ft associated with a solid band of convection in the northeastern quadrant. Using 50 percent of those values supported keeping Fred as a 35-kt tropical storm at 0600 UTC. This intensity was also supported by 30-kt winds on the west side of the low-level circulation noted in surface observations. Since that time, however, the solid band of convection has become fragmented and the thunderstorm activity has broken up into more discrete cells. Satellite and radar imagery also indicate that the mid- and upper-level circulations have decoupled and sheared out to the north of the low-level circulation. As a result, Fred has been downgraded to a tropical depression at the 0900 UTC advisory time. Weakening will continue through today as Fred moves farther inland over Georgia and into the southern Appalachians, with Fred likely becoming a remnant low later tonight before merging with a frontal system over the northern Appalachians on Wednesday. Fred has continued to move north-northeastward, or 015/12 kt. For the remainder of today, Fred should maintain a motion toward the north-northeast or northeast accompanied by a gradual increase forward speed owing to a very stable steering pattern between a deep-layer ridge to the east and a broad mid-tropospheric trough to the west. The new NHC track forecast is essentially just an update of the previous advisory track and lies near the middle of the tightly packed NHC model guidance suite. Although Fred is weakening, the system is still expected to bring flooding rains to portions of the southeastern and eastern United States during the next couple of days. This is the last advisory issued by the National Hurricane Center on Fred. Future information on this system can be found in Public Advisories issued by the Weather Prediction Center beginning at 11 AM ED, under AWIPS header TCPAT1, WMO header WTNT31 KWNH, and on the web at http://www.wpc.ncep.noaa.gov. 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. FORECAST POSITIONS AND MAX WINDS INIT 17/0900Z 32.3N 85.0W 30 KT 35 MPH...INLAND 12H 17/1800Z 34.2N 84.3W 25 KT 30 MPH...INLAND 24H 18/0600Z 37.0N 82.6W 20 KT 25 MPH...POST-TROP/INLAND 36H 18/1800Z 39.6N 80.4W 20 KT 25 MPH...POST-TROP/INLAND 48H 19/0600Z...DISSIPATED $$ Forecaster Stewart
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Hurricane Linda Forecast Discussion Number 29
2021-08-17 10:39:00| Tropical Depression LIDIA
Issued at 1100 PM HST Mon Aug 16 2021
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Tropical Storm Henri Forecast Discussion Number 6
2021-08-17 10:31:26| National Hurricane Center (Atlantic)
Issued at 500 AM AST Tue Aug 17 2021 790 WTNT43 KNHC 170831 TCDAT3 Tropical Storm Henri Discussion Number 6 NWS National Hurricane Center Miami FL AL082021 500 AM AST Tue Aug 17 2021 Earlier this evening Henri was undergoing a sheared bursting pattern, with intermittent deep convection trying to develop near the center, but northwesterly shear would quickly diminish the convective coverage. However, over the past several hours the convection has become more persistent, and covers at least the southeastern portion of the low-level center. As such, the latest subjective Dvorak intensity estimates from TAFB and SAB are now both 3.0 (45 kt), and therefore 45 kt will be the initial advisory intensity. Henri is forecast to remain over warm waters and in an environment of light to moderate northerly shear for the next 24 h, so some strengthening is expected during that time. After 24 h, global models indicate that the shear magnitude will double, which should prevent any further strengthening and possibly weaken the cyclone. The latest NHC intensity forecast was adjusted a little higher than the previous due to both the increase in initial intensity, and slight increase in the model intensity guidance. This forecast closely follows the LGEM solution and is just a little lower than the IVCN consensus. The tropical storm continues to move slowly southwest, or 240/04 kt to the southeast of a mid-level ridge. This ridge is forecast to shift to the east over the next several days, which would result in the tropical storm making a gradual clockwise turn throughout much of the forecast period. Tonight, Henri is forecast to turn westward with a increase in forward motion and pass well south of Bermuda. In a few days, the cyclone should turn to the northwest then north, followed by a turn to the northeast around the western periphery of the ridge. There continues to be some spread in how far west Henri will go before it begins to turn to the north, and the latest guidance has made a slight shift to the left. The official NHC forecast is near the previous one through 48 h, then is a little left of it thereafter, yet still remains to the right of the bulk of the consensus guidance beyond 48 h. FORECAST POSITIONS AND MAX WINDS INIT 17/0900Z 30.6N 63.7W 45 KT 50 MPH 12H 17/1800Z 30.4N 64.4W 50 KT 60 MPH 24H 18/0600Z 30.3N 65.7W 55 KT 65 MPH 36H 18/1800Z 30.2N 67.1W 55 KT 65 MPH 48H 19/0600Z 30.3N 68.6W 55 KT 65 MPH 60H 19/1800Z 30.8N 69.8W 55 KT 65 MPH 72H 20/0600Z 31.6N 70.6W 55 KT 65 MPH 96H 21/0600Z 34.0N 69.1W 55 KT 65 MPH 120H 22/0600Z 36.0N 66.0W 55 KT 65 MPH $$ Forecaster Latto
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Tropical Storm Henri Forecast Discussion Number 5
2021-08-17 06:57:22| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Mon Aug 16 2021 000 WTNT43 KNHC 170456 CCA TCDAT3 Tropical Storm Henri Discussion Number 5...Corrected NWS National Hurricane Center Miami FL AL082021 1100 PM AST Mon Aug 16 2021 Corrected statement in movement section 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 clockwise 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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