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Tropical Storm ERIKA Forecast Discussion Number 1
2015-08-25 04:47:05| National Hurricane Center (Atlantic)
Issued at 1100 PM AST MON AUG 24 2015 000 WTNT45 KNHC 250246 TCDAT5 TROPICAL STORM ERIKA DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052015 1100 PM AST MON AUG 24 2015 Satellite imagery, buoy observations, and a very recent ASCAT pass suggest that the circulation associated with the area of low pressure over the tropical Atlantic has become better defined. Deep convection also became better organized during the afternoon and has persisted in a band over the southeastern portion of the circulation this evening. The NOAA buoy reported peak south- southwesterly winds of 39 kt, and a minimum pressure of 1004 mb. Based on these data, advisories are being initiated on a 40-kt tropical storm. Erika becomes the 5th tropical storm of the 2015 Atlantic hurricane season. During the next couple of days, Erika will be moving through an environment characterized by warm water, a moist air mass, and generally low vertical wind shear. These factors should allow strengthening. After 48 hours, Erika will be approaching an upper-level low/trough that is forecast to be near Hispaniola, which is expected to cause an increase in westerly wind shear. The NHC intensity forecast calls for steady intensification during the next 48 hours, and is close to the SHIPS model and intensity consensus. After that time, the intensity guidance diverges with the statistical guidance and the HWRF bringing Erika to hurricane strength. Meanwhile, the ECMWF and GFS weaken the system in about 3 days, due to the increasing shear. The NHC intensity forecast is between these scenarios and shows no change in strength after 48 hours. Due to the large spread in the intensity guidance, the intensity forecast at days 3-5 is of low confidence. Erika is moving quickly westward across the tropical Atlantic or 275/17 kt. The tropical cyclone is forecast to move westward to west-northwestward to the south of a deep-layer ridge over the central Atlantic during the next few days. The forward speed of Erika should gradually decrease as the cyclone nears the western portion of the ridge. The track guidance is tightly clustered through 72 hours, with more spread after that time. The bifurcation appears to be the result of the future strength of Erika. The models that have a deeper depiction of the cyclone show more of a northwestward turn late in the period, while the models that weaken Erika indicate a more westward motion. The NHC forecast is close to the ECMWF and GFS ensemble mean, which is south of the consensus but not as far south as the GFS. FORECAST POSITIONS AND MAX WINDS INIT 25/0300Z 14.4N 47.7W 40 KT 45 MPH 12H 25/1200Z 14.9N 50.1W 45 KT 50 MPH 24H 26/0000Z 15.8N 53.3W 50 KT 60 MPH 36H 26/1200Z 16.5N 56.4W 55 KT 65 MPH 48H 27/0000Z 17.1N 59.6W 60 KT 70 MPH 72H 28/0000Z 18.5N 64.5W 60 KT 70 MPH 96H 29/0000Z 20.5N 69.5W 60 KT 70 MPH 120H 30/0000Z 22.0N 73.0W 60 KT 70 MPH $$ Forecaster Brown
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