ZCZC MIATCDAT4 ALL TTAA00 KNHC DDHHMM Tropical Depression Isaac Discussion Number 27 NWS National Hurricane Center Miami FL AL092018 500 AM AST Fri Sep 14 2018 Northwesterly shear continues to take a toll on Isaac. Although the system is still producing areas of deep convection, an ASCAT overpass that arrived shortly after the release of the previous advisory, indicated that the circulation had become even less defined. The ASCAT data also showed that the winds are below tropical storm strength, therefore the initial intensity has been reduced to 30 kt. Moderate to strong northwesterly shear and dry mid-level air are likely to cause additional weakening, and Isaac is forecast to degenerate into an open wave within the next several days, but this could occur much sooner if the current trends continue. When the system reaches the western Caribbean Sea the shear may relax somewhat and moisture levels are expected to be higher. These conditions could allow for regeneration of the system, but the ECMWF and GFS both show Issac weakening and moving over the western Caribbean as an open wave, and the NHC forecast follows this scenario. A low- to mid-level ridge over the southwestern Atlantic continues to steer Isaac westward, and this general motion should continue until dissipation occur. The new track forecast is once again essentially an update of the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 14/0900Z 15.0N 65.5W 30 KT 35 MPH 12H 14/1800Z 15.1N 67.3W 30 KT 35 MPH 24H 15/0600Z 15.2N 69.7W 30 KT 35 MPH 36H 15/1800Z 15.2N 72.0W 25 KT 30 MPH 48H 16/0600Z 15.4N 73.8W 25 KT 30 MPH 72H 17/0600Z 16.4N 77.7W 25 KT 30 MPH 96H 18/0600Z...DISSIPATED $$ Forecaster Brown NNNN
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