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Tropical Depression Eighteen Forecast Discussion Number 4
2017-10-28 17:00:30| National Hurricane Center (Atlantic)
Issued at 1100 AM EDT Sat Oct 28 2017 000 WTNT43 KNHC 281500 TCDAT3 Tropical Depression Eighteen Discussion Number 4 NWS National Hurricane Center Miami FL AL182017 1100 AM EDT Sat Oct 28 2017 Data from an Air Force Reserve reconnaissance aircraft indicate that the low pressure system located over the northwestern Caribbean Sea has developed a well-defined low-level circulation center. Satellite imagery also shows more central deep convection has developed and persisted in the inner-core region since yesterday. Based on these data, the disturbance has been upgraded to Tropical Depression Eighteen. With the recent redevelopment of the inner-core region this morning, the initial motion estimate is an uncertain 020/19 kt. The global models remain in excellent agreement on an approaching frontal system and deep mid-tropospheric trough accelerating the cyclone north-northeastward across west-central Cuba today, followed by a motion toward the northeast tonight and Sunday, with the system passing about midway between Bermuda and the southeastern United States in 36-48 hours. The new NHC forecast track is essentially just an update of the previous advisory due to the good agreement in the global and consensus models, which lie along or just a tad to the west of the official forecast track. The vertical wind shear affecting the cyclone is expected to remain somewhat favorable for strengthening to occur for the next 24 hours or so, with the depression expected to become a tropical storm by tonight. Thereafter, baroclinic processes associated with the aforementioned frontal system are forecast to induce some additional strengthening before the cyclone merges with the frontal system and becomes an extratropical low by 48 hours. Dissipation is expected by 72 hours when the system is located over the far North Atlantic. KEY MESSAGES: 1. While the forecast track of the center lies about 35 miles southeast of the Upper Florida Keys and extreme southeast Florida and most of the winds are expected to remain east of the center, only a slight deviation to the west of the expected track or an increase in the size of the wind field could bring tropical-storm- force winds across these land areas. For that reason, a tropical storm watch has been issued for these areas. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 20.8N 82.9W 30 KT 35 MPH 12H 29/0000Z 23.0N 81.8W 35 KT 40 MPH 24H 29/1200Z 26.6N 78.5W 40 KT 45 MPH 36H 30/0000Z 31.5N 74.0W 45 KT 50 MPH 48H 30/1200Z 37.5N 69.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 31/1200Z...DISSIPATED $$ Forecaster Stewart
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