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Tropical Depression TWELVE Forecast Discussion Number 1
2016-09-14 16:42:29| National Hurricane Center (Atlantic)
Issued at 1100 AM AST WED SEP 14 2016 000 WTNT42 KNHC 141442 TCDAT2 TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 1100 AM AST WED SEP 14 2016 Satellite imagery, scatterometer data, and surface observations indicate that the low pressure area over the Cabo Verde Islands has developed a well-defined circulation and sufficient organized convection to be considered a tropical depression. The initial intensity is set at 30 kt based on the scatterometer data along with satellite intensity estimates from TAFB and SAB. The initial motion is 300/12. A low- to mid-level ridge should steer the system west-northwestward and then westward during the forecast period, with some decrease in forward speed after 36 hours as the ridge weakens slightly. The forecast track is near the center of the guidance envelope and close to the various consensus models. Some strengthening is expected during the next 12-24 hours. After that, the cyclone is likely to encounter strong westerly vertical wind shear while over sea surface temperatures of about 26C. This combination should lead to weakening, and the intensity forecast shows the system weakening back to a depression by 36 hours. Near the end of the forecast period, the dynamical models diverge on the evolution of the upper-level winds, with the ECMWF and UKMET forecasting a more favorable pattern than the GFS. Based on this, the forecast shows some re-intensification by 120 hours. An alternative scenario is that the cyclone degenerates to a tropical wave as forecast by the GFS. Overall, the intensity forecast is on the low side of the guidance in best agreement with the LGEM. Locally heavy rains and gusty winds are possible over the Cabo Verde Islands. However, current indications are that the cyclone will not reach tropical-storm strength until it has moved west of the islands. Therefore, watches and warnings are not required at this time. FORECAST POSITIONS AND MAX WINDS INIT 14/1500Z 17.0N 25.0W 30 KT 35 MPH 12H 15/0000Z 17.5N 26.8W 35 KT 40 MPH 24H 15/1200Z 17.9N 29.3W 35 KT 40 MPH 36H 16/0000Z 17.9N 31.7W 30 KT 35 MPH 48H 16/1200Z 17.8N 34.0W 30 KT 35 MPH 72H 17/1200Z 17.5N 38.0W 30 KT 35 MPH 96H 18/1200Z 17.5N 41.5W 35 KT 40 MPH 120H 19/1200Z 18.0N 45.5W 40 KT 45 MPH $$ Forecaster Beven
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