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Tropical Depression TWELVE Forecast Discussion Number 2
2016-09-14 22:40:53| National Hurricane Center (Atlantic)
Issued at 500 PM AST WED SEP 14 2016 000 WTNT42 KNHC 142040 TCDAT2 TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 500 PM AST WED SEP 14 2016 The depression has not become better organized since the last advisory, with the most concentrated convection now in a cluster just west of the estimated center position. The initial intensity remains 30 kt in best agreement with a satellite intensity estimate from SAB. The initial motion is a somewhat uncertain 295/13 kt. 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 36-48 hours as the ridge weakens slightly. The new forecast track is similar to, but a little north of, the previous track based on a slight northward shift in the track guidance. Some strengthening is expected during the next 12 hours or so. After that, the cyclone will encounter strong westerly vertical wind shear caused by a developing upper-level trough near and north of the cyclone. This, combined with passage over sea-surface temperatures of about 26C-27C, 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 continue to diverge on the evolution of the upper-level winds, with the ECMWF and UKMET forecasting a more favorable ridge pattern near the cyclone, whereas the GFS has an upper-level trough close by. Based on these conflicting models, the forecast leans toward the ECMWF/UKMET scenario and shows some re-intensification by 120 hours. An alternative scenario is that the cyclone degenerates into a broad low pressure area or tropical wave as forecast by the GFS. Overall, the intensity forecast remains on the low side of the guidance in best agreement with the LGEM. Gusty winds remain possible over the Cabo Verde Islands tonight, whereas locally heavy rains will remain possible through Thursday. FORECAST POSITIONS AND MAX WINDS INIT 14/2100Z 17.4N 26.5W 30 KT 35 MPH 12H 15/0600Z 17.9N 28.4W 35 KT 40 MPH 24H 15/1800Z 18.0N 30.8W 35 KT 40 MPH 36H 16/0600Z 18.1N 33.2W 30 KT 35 MPH 48H 16/1800Z 18.1N 35.6W 30 KT 35 MPH 72H 17/1800Z 18.0N 39.5W 30 KT 35 MPH 96H 18/1800Z 17.5N 43.5W 35 KT 40 MPH 120H 19/1800Z 18.0N 47.5W 40 KT 45 MPH $$ Forecaster Beven
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