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Tropical Storm ERIKA Forecast Discussion Number 15
2015-08-28 16:52:11| National Hurricane Center (Atlantic)
Issued at 1100 AM AST FRI AUG 28 2015 000 WTNT45 KNHC 281452 TCDAT5 TROPICAL STORM ERIKA DISCUSSION NUMBER 15 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052015 1100 AM AST FRI AUG 28 2015 Morning visible imagery shows that the broad low-level center of Erika is exposed to the west of the main convective area due to the effects of 20-25 kt of westerly vertical wind shear. An Air Force Reserve Hurricane Hunter aircraft has reported a large area of 40-45 kt surface wind estimates from the Stepped Frequency Microwave Radiometer and 850 mb flight-level winds as high as 55 kt, so the initial intensity remains 45 kt. The central pressure based on the aircraft reports is 1008 mb. Now that the center is somewhat easier to locate, the initial motion is a somewhat more confident 285/16. A generally west-northwestward motion is expected for the next 48 hours or so as Erika moves around the southwestern periphery of the subtropical ridge. After that time, a northwestward and northward turn and a decrease in forward speed are forecast as Erika moves between the ridge and a mid- to upper-level trough over the Gulf of Mexico. The track guidance continues to show some spread based on the forecast strength of Erika. The models with a stronger cyclone, such as the GFDL and GFS, show a faster northward turn and are on the eastern side of the guidance envelope. On the other hand, the ECMWF forecasts a weaker storm and lies on the left side of the envelope. An extra complication is that passage over Hispaniola is likely to disrupt the circulation, with the possibility that the center could reform somewhere northwest or west of the island. Overall, the guidance envelope has shifted a little to the west since the previous advisory, and the new forecast track shows a similar nudge through 96 hours. The guidance is also showing a faster forward speed than six hours ago, so the new track is also a little faster than the previous track. Westerly to southwesterly vertical wind shear is forecast to continue or increase during the next 12 to 24 hours. This, combined with land interaction, suggests that the cyclone should weaken, and there is a chance the system could degenerate to a tropical wave while crossing Hispaniola. Assuming the cyclone survives, the shear should decrease some after 36 hours, which could allow some strengthening up to the time of possible landfall on the Florida Peninsula. The new intensity forecast is an update of the previous forecast, and like the previous forecast it is low confidence. The greatest short-term threat posed by Erika continues to be very heavy rainfall over portions of the Dominican Republic and Haiti today and tonight. These rains could produce flash floods and mud slides. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 17.7N 69.4W 45 KT 50 MPH 12H 29/0000Z 19.3N 71.4W 40 KT 45 MPH...INLAND 24H 29/1200Z 20.8N 74.5W 40 KT 45 MPH...OVER WATER 36H 30/0000Z 22.3N 77.3W 40 KT 45 MPH 48H 30/1200Z 23.5N 79.2W 45 KT 50 MPH 72H 31/1200Z 26.0N 81.5W 50 KT 60 MPH...INLAND 96H 01/1200Z 28.5N 82.0W 40 KT 45 MPH...INLAND 120H 02/1200Z 30.5N 82.0W 35 KT 40 MPH...INLAND $$ Forecaster Beven
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