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Tropical Storm ERIKA Forecast Discussion Number 13
2015-08-28 05:04:10| National Hurricane Center (Atlantic)
Issued at 1100 PM AST THU AUG 27 2015 000 WTNT45 KNHC 280304 TCDAT5 TROPICAL STORM ERIKA DISCUSSION NUMBER 13 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052015 1100 PM AST THU AUG 27 2015 The center of Erika is not easy to locate tonight, and it appears that a few smaller swirls are rotating within a larger gyre. In fact, one of these small swirls moved near St. Croix producing tropical storm force wind gusts during the past few hours on the island. Due to the lack of an inner core, the initial position is based on a mean center of circulation. Despite the poor organization, the reconnaissance plane currently in Erika was able to measure 700 mb flight-level winds of 59 kt well to the southeast of the alleged center. Based on the SFMR, these winds are not at the surface, and the initial intensity is kept at 40 kt. The central pressure is not falling, which is another indication that Erika is not strengthening. The NHC forecast calls for no change in intensity during the next 36 hours, given the fact that cyclone will be moving through a very hostile shear environment, and will also feel the effects of land. Once in the Bahamas, however, the upper-level flow is expected to become more favorable, and if Erika survives, it has the opportunity to strengthen some. The NHC forecast is very close to the intensity consensus and is similar to the previous one. The best estimate of the initial motion is toward the west or 270 degrees at 15 kt, and this estimate is highly uncertain. Erika should begin to turn toward the west-northwest during the next several hours around the periphery of the western Atlantic subtropical ridge, and should reach the Central Bahamas between 36 and 48 hours. By then, the cyclone will be located on the southwestern edge of the ridge, and should begin to turn to the northwest with decreasing forward speed. Most of the track guidance, including the ECMWF and the GFS global models, show a tropical cyclone approaching southeast Florida in about 3 days and moving northward near or over the east coast of Florida during the latter portion of the forecast period. There is unusually high uncertainty in this forecast, especially at days 3 to 5, given that the cyclone has to recover from shear and from the effects of land for this to occur. The greatest short-term threat posed by Erika continues to be very heavy rainfall over portions of the northern Leeward Islands tonight, and over the Virgin Islands and Puerto Rico on Friday. These rains could produce flash floods and mud slides. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 16.6N 65.3W 40 KT 45 MPH 12H 28/1200Z 18.2N 67.4W 40 KT 45 MPH 24H 29/0000Z 19.7N 70.2W 40 KT 45 MPH 36H 29/1200Z 21.1N 73.2W 40 KT 45 MPH 48H 30/0000Z 22.5N 75.5W 45 KT 50 MPH 72H 31/0000Z 25.2N 79.0W 55 KT 65 MPH 96H 01/0000Z 27.3N 80.2W 65 KT 75 MPH 120H 02/0000Z 29.5N 80.7W 75 KT 85 MPH $$ Forecaster Avila
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