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Tropical Depression Claudette Forecast Discussion Number 10
2021-06-20 04:40:05| National Hurricane Center (Atlantic)
Issued at 1000 PM CDT Sat Jun 19 2021 000 WTNT43 KNHC 200239 TCDAT3 Tropical Depression Claudette Discussion Number 10 NWS National Hurricane Center Miami FL AL032021 1000 PM CDT Sat Jun 19 2021 Although the center is well inland, Claudette has become better organized during the past several hours, with a large area of convection forming close to the center in the northern quadrant. In addition to this convection, a large area of rain bands is present over the eastern semicircle from the northeastern Gulf of Mexico northward into southeastern Tennessee Surface observation indicate that the maximum winds have decreased a little more and are now 25 kt, with these winds mainly over the Gulf of Mexico to the south of the center. Surface observations also indicate that the central pressure is 1005-1006 mb. The initial motion is still northeastward, but is a little slower than before, 050/12 kt. A turn to the east-northeast is expected during the next 6-12 h as Claudette moves in the westerlies on the north side of the subtropical ridge. This motion should take the system across portions of the southeast U.S. during the next 36 h or so and then over the western Atlantic and toward Atlantic Canada with a significant increase in forward speed between 36- 72 h. The track forecast guidance remains tightly clustered and has changed little since the last advisory. So, the new forecast track is basically an update of the previous forecast, and it calls for the system to be near the coast of North Carolina at about the 36 h point. The intensity guidance continues to show a sizable amount of spread. On one side, the GFS has an ill-defined system reaching the Carolina coast in 36 h, with only minimal subsequent intensification after Claudette moves into the Atlantic. On the other side, the UKMET shows the central pressure falling below 1000 mb before the system reaches the Atlantic and winds exceeding 50 kt once the system is over water. The ECMWF and Canadian models lie between these extremes. The model forecasts do not show any strong baroclinic forcing that would lead to the level of intensification shown by the UKMET. On the other hand, the short-term trends in the cyclone's organization currently favor the stronger model forecasts. Given the uncertainty, the intensity forecast is not changed much from the previous forecast, except for moving the time of dissipation up by 24 h as Claudette gets absorbed into a large extratropical low over eastern Canada. If the current trends continue, or later GFS runs forecast a stronger system, the intensity forecast could be adjusted upward in later advisories. It should be noted that even the weaker GFS solution brings 30-35 kt winds to the North Carolina coast near the 36 h point, and a tropical storm warning will likely be required for a portion of the current watch area on the next advisory. Key Messages: 1. Claudette is expected to produce heavy rainfall and flash flooding across portions of the Florida Panhandle, northern Alabama, and Georgia through tonight, and into the Carolinas on Sunday. Considerable flash, urban, and small stream flooding impacts are possible across these areas. 2. Tropical storm conditions are possible along portions of the North Carolina coast Sunday night and Monday, where a Tropical Storm Watch is in effect. Tropical Storm Warnings will likely be required for portions of this area early Sunday. FORECAST POSITIONS AND MAX WINDS INIT 20/0300Z 32.6N 87.0W 25 KT 30 MPH...INLAND 12H 20/1200Z 33.3N 84.7W 25 KT 30 MPH...INLAND 24H 21/0000Z 34.2N 81.0W 30 KT 35 MPH...INLAND 36H 21/1200Z 35.4N 76.6W 35 KT 40 MPH...INLAND 48H 22/0000Z 37.7N 71.9W 40 KT 45 MPH...OVER WATER 60H 22/1200Z 40.8N 66.7W 40 KT 45 MPH 72H 23/0000Z 44.5N 60.8W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 24/0000Z...DISSIPATED $$ Forecaster Beven
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