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Tropical Depression EIGHT Forecast Discussion Number 1
2015-09-09 06:26:03| National Hurricane Center (Atlantic)
Issued at 1230 AM AST WED SEP 09 2015 000 WTNT43 KNHC 090425 TCDAT3 TROPICAL DEPRESSION EIGHT SPECIAL DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL082015 1230 AM AST WED SEP 09 2015 A recent ASCAT-B overpass indicates that the low pressure area east-southeast of Bermuda has developed a well-defined circulation with winds of at least 30 kt in the northeastern quadrant. In addition, a strong cluster of convection has been persisting in the eastern quadrant. Based on these developments, advisories are being initiated on Tropical Depression Eight. It should be noted that the system has a large radius of maximum winds more characteristic of a subtropical cyclone. However, data from the FSU phase space analysis and the strong convection suggest the system is more tropical than subtropical. The cyclone is currently nearly stationary. A northward motion should begin on Wednesday as a deep layer trough moves into the eastern United States and weakens the subtropical ridge. The cyclone is expected to enter the westerlies and turn toward the northeast after 48 hours, with this motion continuing until dissipation. The forecast track lies in the center of the track guidance envelope in good agreement with the various consensus models. An upper-level trough just west of the cyclone is currently providing upper-level difluence, and this is likely enhancing the convection. The dynamical models forecast the cyclone to become embedded in about 15 kt of southerly vertical wind shear on the east side of the trough. While there is dry air entraining into the cyclone, the environment should allow for some slow strengthening through 72 hours while the system remains over warm water. Thus, the intensity forecast calls for strengthening in best agreement with a blend of the SHIPS and LGEM models. After 72 hours, the cyclone is expected to merge with a frontal system and lose its identity by 120 hours. FORECAST POSITIONS AND MAX WINDS INIT 09/0430Z 30.8N 61.5W 30 KT 35 MPH 12H 09/1200Z 30.8N 61.5W 35 KT 40 MPH 24H 10/0000Z 31.6N 61.5W 40 KT 45 MPH 36H 10/1200Z 33.4N 61.9W 45 KT 50 MPH 48H 11/0000Z 36.0N 62.2W 50 KT 60 MPH 72H 12/0000Z 43.0N 60.5W 50 KT 60 MPH 96H 13/0000Z 48.0N 45.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 14/0000Z...DISSIPATED $$ Forecaster Beven
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