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Tropical Depression Four Forecast Discussion Number 4
2017-07-06 22:32:49| National Hurricane Center (Atlantic)
Issued at 500 PM AST Thu Jul 06 2017 000 WTNT44 KNHC 062032 TCDAT4 Tropical Depression Four Discussion Number 4 NWS National Hurricane Center Miami FL AL042017 500 PM AST Thu Jul 06 2017 It's difficult to tell from visible and microwave satellite imagery whether or not the depression still has a closed surface circulation. In addition, the forward speed is now about 20 kt, which would make it difficult for a 25-kt depression to maintain westerly winds to the south of the center. For now, advisories will be maintained until/if there is stronger evidence that the circulation has opened up. Convective cloud tops have warmed during the past few hours, and Dvorak final-T numbers from TAFB and SAB have decreased. Therefore, the initial intensity will be held at 25 kt based on continuity. Multispectral satellite imagery shows the Saharan Air Layer is overtaking the depression, and it will be increasingly more difficult for the system to maintain organized deep convection. It has also become more likely that the cyclone will not strengthen beyond its current intensity. The global models indicate that southwesterly to westerly deep-layer shear will increase in about 36 hours, at which point the NHC official forecast now shows the depression degenerating to a remnant low. However, it's entirely possible that the cyclone could open up into a tropical wave at any time. Based on the estimated center location, the depression has not gained much latitude today, and the initial motion estimate is 275/20 kt. The global models remain persistent that the cyclone should turn west-northwestward in about 24 hours as it approaches a break in the subtropical ridge, and they are generally in very close agreement on the future track and forward speed through at least 48 hours. The updated NHC track forecast is nudged southward to account for the recent motion, but otherwise it is an update of the previous forecast. FORECAST POSITIONS AND MAX WINDS INIT 06/2100Z 13.1N 44.9W 25 KT 30 MPH 12H 07/0600Z 13.8N 47.8W 25 KT 30 MPH 24H 07/1800Z 14.9N 51.5W 25 KT 30 MPH 36H 08/0600Z 16.2N 55.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 08/1800Z 17.8N 58.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 09/1800Z 20.9N 64.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 10/1800Z...DISSIPATED $$ Forecaster Berg
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