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Tropical Depression NINE Forecast Discussion Number 6
2016-08-30 04:50:07| National Hurricane Center (Atlantic)
Issued at 1000 PM CDT MON AUG 29 2016 000 WTNT44 KNHC 300249 TCDAT4 TROPICAL DEPRESSION NINE DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092016 1000 PM CDT MON AUG 29 2016 Since the previous advisory, the depression's convective pattern has improved somewhat with the development of a cluster of deep convection with tops to -80C having developed near and also east through south of the center. Reports from nearby ships WAHV, J8NY, and C6CL6, along with reconnaissance data indicate that the low-level circulation is slowly improving. The central pressure of 1003 mb is based on a recent NOAA dropsonde report of 1005 mb with 20 kt of wind just north of the center. Since no winds of tropical storm force were sampled, the initial intensity remains at 30 kt. Similar to this time last night, the cyclone has made a jog to the west during the earlier convective hiatus period. However, the past couple of dropsonde reports suggest that the depression has resumed a longer term motion of 280/06 kt. There is little change to the previous forecast track reasoning. Other than having to adjust the forecast track southward slightly through 48 hours due to the more southerly initial position, the previous advisory track remains unchanged. The cyclone is forecast to move slowly around the western periphery of a deep-layer subtropical ridge located over southern Florida for the next 36 hours or so. By 48 hours, the depression is expected to accelerate northeastward across northern Florida ahead of a shortwave trough that is forecast to dig southeastward into the southeastern United States and northern Gulf Mexico. The new NHC track forecast lies between a blend of the GFS-ECMWF solutions and the consensus model TVCN. Data from the NOAA aircraft on its final outbound leg, along with the latest 00Z upper-air observations indicate that mid-level moisture north and northeast of the cyclone has increased since yesterday. However, water vapor imagery and upper-air data still indicate that very dry air lies just west of the cyclone across the central and western Gulf of Mexico. The global and regional models continue to indicate that some of that drier air will be entrained into the western part of the cyclone's circulation by 24-36 hours, offsetting the otherwise favorable upper-level outflow pattern and very warm SSTs of more than 30 deg C. Therefore, only gradual intensification is expected during the next 48 hours or so. When the cyclone nears the Florida Gulf coast, increasing upper-level winds are expected to limit strengthening. The official intensity forecast lies close to the previous advisory and consensus model IVCN. Given the current forecast, a tropical storm or hurricane watch may be required for a portion of the Florida Gulf coast by tomorrow morning. FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 23.9N 85.5W 30 KT 35 MPH 12H 30/1200Z 24.2N 86.4W 35 KT 40 MPH 24H 31/0000Z 24.9N 87.1W 40 KT 45 MPH 36H 31/1200Z 25.8N 87.0W 45 KT 50 MPH 48H 01/0000Z 27.2N 85.8W 55 KT 65 MPH 72H 02/0000Z 30.1N 82.2W 50 KT 60 MPH...INLAND 96H 03/0000Z 33.1N 75.5W 50 KT 60 MPH...OVER WATER 120H 04/0000Z 35.8N 68.7W 50 KT 60 MPH $$ Forecaster Stewart
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