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Tropical Storm Isaac Forecast Discussion Number 7
2018-09-09 10:40:41| National Hurricane Center (Atlantic)
Issued at 500 AM AST Sun Sep 09 2018 335 WTNT44 KNHC 090840 TCDAT4 Tropical Storm Isaac Discussion Number 7 NWS National Hurricane Center Miami FL AL092018 500 AM AST Sun Sep 09 2018 The cloud pattern of Isaac has changed significantly during the past several hours. The storm no longer has a sheared appearance, and instead microwave images reveal a well-defined curved band that wraps a little more than halfway around the center. Despite the change in the storm's structure, the Dvorak classifications are unchanged at 3.0/45 kt. Based on that data, the initial intensity is held at 45 kt for this advisory. Now that the shear has lessened, Isaac should steadily strengthen during the next few days as the storm remains over warm waters and in a low wind shear environment. Beyond a few days, however, the SHIPS model shows a notable increase in shear, in part due to the outflow from Florence, which should end the strengthening trend and induce some weakening. There was no significant change in the intensity guidance this cycle, so the official forecast is largely an update of the previous one. This prediction lies fairly close to the IVCN and HCCA models. Isaac remains on the forecast track and the initial motion is the same as before, 270/7. 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. Although there is some spread in the models, the usually more reliable GFS and ECMWF models have been consistent in showing a due westward motion through the forecast period. The NHC track forecast leans toward those models, and it is fairly similar to the previous prediction. 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 09/0900Z 14.5N 38.1W 45 KT 50 MPH 12H 09/1800Z 14.6N 39.6W 55 KT 65 MPH 24H 10/0600Z 14.7N 41.9W 60 KT 70 MPH 36H 10/1800Z 14.7N 44.6W 70 KT 80 MPH 48H 11/0600Z 14.7N 47.5W 80 KT 90 MPH 72H 12/0600Z 14.7N 53.1W 85 KT 100 MPH 96H 13/0600Z 14.9N 58.9W 80 KT 90 MPH 120H 14/0600Z 15.3N 64.5W 70 KT 80 MPH $$ Forecaster Cangialosi
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