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Tropical Storm ERIKA Forecast Discussion Number 7
2015-08-26 16:46:57| National Hurricane Center (Atlantic)
Issued at 1100 AM AST WED AUG 26 2015 000 WTNT45 KNHC 261446 TCDAT5 TROPICAL STORM ERIKA DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052015 1100 AM AST WED AUG 26 2015 Deep convection associated with Erika has increased during the past 24 hours, but the overall organization of the tropical cyclone has not changed very much. Reconnaissance aircraft data indicate that the center is located near the northwestern edge of the thunderstorm activity due to moderate northwesterly shear. The aircraft has measured believable SFMR winds of around 40 kt this morning, and the initial intensity is set at that value. Erika is forecast to pass through an environment of moderate to strong westerly vertical wind shear during the next two to three days. The shear will be caused by an upper-level low that is expected to remain near eastern Cuba through Friday. The upper low is forecast to weaken on Saturday, which should produce a more conducive upper-level wind pattern over the Bahamas. The NHC intensity forecast calls for little change in strength through 72 hours, which is in line with the latest statistical guidance. After that time, strengthening is indicated due to the expected more favorable upper-level environment. The official forecast lies between the more robust HWRF/GFDL and lower statistical guidance. An alternative forecast scenario, supported by the GFS model, is that Erika weakens to a tropical wave due to the shear and interaction with the Greater Antilles. The amount of strengthening on days 4-5 will be dependent in part on how Erika responds to the the preceding unfavorable shear. The initial motion estimate is 280/15 kt. Erika is expected to move westward to west-northwestward during the next several days to the south of a subtropical ridge over the western Atlantic. The track guidance is in good agreement through much of the forecast period, with the exception of the GFDL model that takes a stronger storm northwestward much sooner. The new NHC track is essentially an update of the previous advisory and is close to a consensus of the ECMWF, GFS, HWRF, and UKMET. This is also in good agreement with the Florida State Superensemble. One should remember to not focus on the exact forecast track, especially at the long range where the average NHC track errors during the past 5 years are about 180 miles at day 4 and 240 miles at day 5. FORECAST POSITIONS AND MAX WINDS INIT 26/1500Z 16.1N 57.6W 40 KT 45 MPH 12H 27/0000Z 16.7N 59.9W 45 KT 50 MPH 24H 27/1200Z 17.6N 63.0W 45 KT 50 MPH 36H 28/0000Z 18.7N 65.9W 45 KT 50 MPH 48H 28/1200Z 19.8N 68.7W 45 KT 50 MPH 72H 29/1200Z 22.0N 73.7W 45 KT 50 MPH 96H 30/1200Z 24.4N 77.7W 55 KT 65 MPH 120H 31/1200Z 26.5N 80.5W 65 KT 75 MPH...INLAND $$ Forecaster Brown
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