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Tropical Storm Isaac Forecast Discussion Number 6
2018-09-09 04:42:09| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Sat Sep 08 2018 251 WTNT44 KNHC 090242 TCDAT4 Tropical Storm Isaac Discussion Number 6 NWS National Hurricane Center Miami FL AL092018 1100 PM AST Sat Sep 08 2018 Isaac is strengthening this evening. Satellite images indicate that the deep convection has been increasing in intensity and coverage with better defined banding features. The center is not located in the center of the convection, however, due to some easterly shear. An ASCAT pass around 00Z showed maximum winds in the 40-45 kt range. These data are also in line with the latest Dvorak classifications of 3.0/45 kt from TAFB and SAB. Based on these estimates, the initial intensity is raised to 45 kt. Isaac will likely continue to strengthen during the next few days as the storm remains over warm waters and moves into an environment of decreasing wind shear. Beyond a few days, the SHIPS model shows a notable increase in shear, in part due to the outflow from Florence, which should end the strengthening trend and cause some weakening. With the exception of the HMON and COAMPS-TC models, the remainder of the intensity guidance is higher this cycle. The NHC intensity forecast is raised from the previous one, but it is a little lower than the HCCA and IVCN guidance. The storm is moving due westward at 7 kt. The track forecast seems fairly straightforward. A strengthening subtropical ridge to the north of the system should cause Isaac to move westward at an increasing forward speed during the next several days. This scenario is supported by the usually more reliable GFS and ECMWF models, and the NHC track forecast is near a blend of those aids. Based on the current forecast, Isaac will be near the Lesser Antilles in 4 to 5 days and interests there should monitor the progress of this system. FORECAST POSITIONS AND MAX WINDS INIT 09/0300Z 14.4N 37.5W 45 KT 50 MPH 12H 09/1200Z 14.4N 38.7W 50 KT 60 MPH 24H 10/0000Z 14.5N 40.9W 60 KT 70 MPH 36H 10/1200Z 14.5N 43.5W 70 KT 80 MPH 48H 11/0000Z 14.5N 46.1W 75 KT 85 MPH 72H 12/0000Z 14.5N 51.5W 85 KT 100 MPH 96H 13/0000Z 14.6N 57.0W 80 KT 90 MPH 120H 14/0000Z 15.0N 62.9W 75 KT 85 MPH $$ Forecaster Cangialosi
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