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Chill falls over the Atlantic as the official season heads towards close
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| #873346 (Received by flhurricane at: 4:56 AM 30.Aug.2016) TCDAT4 TROPICAL DEPRESSION NINE DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092016 400 AM CDT TUE AUG 30 2016 Although there has been an increase in convection over the southeastern portion of the depression's circulation, the system is still being affected by westerly shear, with the low-level center exposed to the west of the deep convection. Recent observations from a NOAA Hurricane Hunter aircraft and the unmanned NASA Global Hawk indicate that the tropical cyclone remains just below tropical storm strength. The NOAA aircraft has reported peak flight level winds in the southeastern quadrant of 32 kt, and believable SFMR winds of around 30 kt. A dropsonde from the Global Hawk reported 33 kt surface winds, but the mean-layer wind over the lowest 150 m support winds closer to 30 kt. A very recent center drop from the unmanned aircraft indicate that the minimum pressure is 1003 mb. The westerly shear over the depression is forecast to decrease somewhat during the next day or so, however dry mid-level air is expected to remain near and to the west of the system. As a result of the marginal environment, only gradual strengthening is predicted during the next couple of days. This is supported by the global models which do not significantly deepen the system until is moves over the western Atlantic and interacts with an upper-level trough. The NHC intensity forecast is unchanged from the previous advisory and remains near the intensity consensus model IVCN. The aircraft fixes show that the depression has moved westward since the previous advisory, and the initial motion estimate is 275/6 kt. The cyclone is forecast to turn west-northwestward, then northwestward tonight around a low- to mid-level ridge over the western Atlantic and Florida. After that time, a deepening mid-latitude trough over the southeastern United States should cause the system to turn northeastward toward the Florida Big Bend region. The dynamical models continue to agree on this scenario, but there are some differences in the forward speed of the system after 36 hours, and the NHC track is near the consensus of the GFS and ECMWF models. The more westward initial position has required a westward adjustment to the track through 24 hours, but otherwise, the new NHC track forecast is similar to the previous advisory. Given the current forecast, a tropical storm or hurricane watch may be required for a portion of the Florida Gulf coast later today. FORECAST POSITIONS AND MAX WINDS INIT 30/0900Z 23.8N 86.6W 30 KT 35 MPH 12H 30/1800Z 24.2N 87.3W 35 KT 40 MPH 24H 31/0600Z 24.9N 87.6W 40 KT 45 MPH 36H 31/1800Z 26.2N 86.9W 45 KT 50 MPH 48H 01/0600Z 27.7N 85.5W 55 KT 65 MPH 72H 02/0600Z 30.7N 81.1W 50 KT 60 MPH 96H 03/0600Z 33.2N 74.0W 50 KT 60 MPH 120H 04/0600Z 35.5N 67.5W 50 KT 60 MPH $$ Forecaster Brown |
