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Tropical Depression FOUR Forecast Discussion Number 1
2014-08-23 22:48:54| National Hurricane Center (Atlantic)
Issued at 500 PM AST SAT AUG 23 2014 000 WTNT44 KNHC 232048 TCDAT4 TROPICAL DEPRESSION FOUR DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL042014 500 PM AST SAT AUG 23 2014 The Air Force Reserve Hurricane Hunter aircraft investigating the disturbance near the southeastern Bahamas found a well-defined circulation this afternoon. Even though the convective presentation is somewhat ragged, there is enough organization to classify the system as a tropical cyclone. The intensity is set to 30 kt based on flight level wind data from the aircraft and an earlier ASCAT pass, and the central pressure of 1005 mb is based on a recent surface observation from Providenciales in the Turks and Caicos. The SHIPS model shows light to moderate shear over the cyclone for the next couple of days, which should allow for intensification given that the cyclone will be moving over waters of 29 to 30C. The NHC forecast shows slow strengthening in the first 24 to 36 hours as the cyclone organizes. Global models show more favorable upper- level winds over the system in a couple of days, which should allow for strengthening to a hurricane in by 3 days. The official forecast is close to the IVCN intensity consensus through the period. The initial motion estimate is a relatively uncertain 310/10 given the recent formation of the center. The cyclone should continue moving northwestward and north-northwestward into a developing break in the subtropical ridge cause by a mid/upper-level trough off the U.S. east coast. As the trough begins to lift out and steering currents weaken, a slow motion is expected in 36 to 48 hours. Then as a subtropical ridge rebuilds to the east of the cyclone later in the period, the system is expected to turn northward and then northeastward. However, there is significant disagreement in the timing and sharpness of the turn in this and previous dynamical model cycles. Currently the GFDL and GFS are along the western edge of the guidance envelope showing a more westward track and a slower motion at day 5. The ECMWF, GEFS mean, and HWRF show a sharper turn and a more northeastward motion by day 5 on the east side of the guidance envelope. The NHC forecast is near the TVCA multi-model consensus through most of the period and a little to the left of it at day 5. Given the spread in the guidance and the recent formation of the system, confidence in the details of the track forecast is lower than normal. FORECAST POSITIONS AND MAX WINDS INIT 23/2100Z 21.8N 72.3W 30 KT 35 MPH 12H 24/0600Z 22.9N 73.6W 35 KT 40 MPH 24H 24/1800Z 24.0N 74.4W 40 KT 45 MPH 36H 25/0600Z 24.6N 74.8W 45 KT 50 MPH 48H 25/1800Z 25.0N 75.0W 55 KT 65 MPH 72H 26/1800Z 26.5N 76.0W 65 KT 75 MPH 96H 27/1800Z 29.0N 77.5W 65 KT 75 MPH 120H 28/1800Z 32.0N 76.5W 70 KT 80 MPH $$ Forecaster Brennan
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