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Tropical Storm ERIKA Forecast Discussion Number 2
2015-08-25 10:38:23| National Hurricane Center (Atlantic)
Issued at 500 AM AST TUE AUG 25 2015 000 WTNT45 KNHC 250838 TCDAT5 TROPICAL STORM ERIKA DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052015 500 AM AST TUE AUG 25 2015 The cloud pattern of Erika has not changed much overnight, with the convection located near the center and in the southern semicircle. The latest Dvorak estimates are T2.5/35 kt from TAFB and SAB, and the initial intensity remains 40 kt based on the earlier buoy data. Erika will be moving over warming SSTs with light to moderate shear for the next 36 to 48 hours, and the NHC forecast shows steady intensification during this time. After that, Erika could encounter increasing westerly shear due to interaction with an upper-level low near Hispaniola and there is the potential for land interaction with the Greater Antilles. The HWRF and LGEM models show more strengthening during this time, while the GFDL and SHIPS models are less aggressive. There is also disagreement among the global models. The GFS weakens Erika to a trough by 5 days while the ECMWF has trended stronger and the UKMET continues to show a more robust cyclone. The NHC intensity forecast has been adjusted upward a bit at days 4 and 5 and is close to or a bit below the IVCN intensity consensus. Due to the large spread in the guidance, the intensity forecast at days 3-5 is of even lower confidence than usual. The initial motion estimate of 275/17 is based largely on continuity, given the difficulty locating the center with infrared imagery. The track guidance is in good agreement through 36 hours, as Erika should be steered westward to west-northwestward south of the subtropical ridge. At 48 hours and beyond, there are two distinct camps of track guidance. The UKMET, HWRF, and GFDL show a deeper system that moves northwestward, while the GFS, ECMWF, and GEFS ensemble mean show a weaker cyclone and a more west- northwestward motion. The NHC forecast has been nudged a bit to the right this cycle and remains close to the ECMWF and GEFS ensemble mean. This track is to the right of the GFS but well left of the TVCA multi-model consensus. Given the divergence in the guidance, confidence in the track forecast late in the period is low. Based on the new forecast, Tropical Storm Watches have been issued for portions of the Lesser Antilles. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 14.6N 49.4W 40 KT 45 MPH 12H 25/1800Z 15.2N 51.9W 45 KT 50 MPH 24H 26/0600Z 16.0N 54.8W 50 KT 60 MPH 36H 26/1800Z 16.9N 57.9W 55 KT 65 MPH 48H 27/0600Z 17.6N 61.0W 60 KT 70 MPH 72H 28/0600Z 19.3N 66.2W 60 KT 70 MPH 96H 29/0600Z 21.5N 71.0W 65 KT 75 MPH 120H 30/0600Z 24.0N 75.0W 70 KT 80 MPH $$ Forecaster Brennan
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