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Tropical Depression Eleven Forecast Discussion Number 1
2021-08-29 04:49:54| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Sat Aug 28 2021 023 WTNT41 KNHC 290249 TCDAT1 Tropical Depression Eleven Discussion Number 1 NWS National Hurricane Center Miami FL AL112021 1100 PM AST Sat Aug 28 2021 Before sunset this evening, visible satellite images showed that a well-defined low level circulation was developing in association with the disturbance over the subtropical central Atlantic. However, up until a couple of hours ago, the system lacked sufficient organized deep convection to be considered a tropical cyclone by definition. Since that time, a deep convective burst has increased in size near, and to the east of the estimated center. In addition, a curved band has begun to develop over the southeastern portion of the circulation. Based on this increase in convective organization, advisories are being initiated on Tropical Depression Eleven. There was no ASCAT data this evening over the cyclone, so the initial intensity of 30 kt is based on the latest Dvorak CI number from TAFB. The initial motion of the depression is 050/10 kt. The cyclone is embedded in southwesterly flow to the southeast of a mid- to upper-level trough and an associated cold front. This flow is forecast to increase as the cold front approaches the cyclone, resulting in the system accelerating northeastward over the next day or so. Once the cyclone interacts with this frontal boundary in a couple of days, a turn to the north is expected. The model guidance is in very good agreement on this scenario, and the NHC track forecast lies in the middle of the consensus tracks. Baroclinic forcing and upper-level diffluence should aid in intensifying the depression over the next 24 h, despite increasing shear. By 36 h, the combination of interaction with the cold front and passage over much cooler waters should result in extratropical transition. The system is then forecast to become absorbed by a larger low pressure system by midweek. The NHC intensity forecast is near the various multi-model consensus solutions. FORECAST POSITIONS AND MAX WINDS INIT 29/0300Z 33.0N 49.7W 30 KT 35 MPH 12H 29/1200Z 34.6N 47.1W 35 KT 40 MPH 24H 30/0000Z 36.8N 43.4W 45 KT 50 MPH 36H 30/1200Z 39.5N 39.2W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 31/0000Z 43.4N 36.4W 45 KT 50 MPH...POST-TROP/EXTRATROP 60H 31/1200Z 47.9N 36.3W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 01/0000Z...DISSIPATED $$ Forecaster Latto
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