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| #799046 (Received by flhurricane at: 4:56 PM 28.Aug.2015) TCDAT5 TROPICAL STORM ERIKA DISCUSSION NUMBER 16 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052015 500 PM EDT FRI AUG 28 2015 The low-level center of Erika continues to be be located west of the convection due to the impact of 25-30 kt of westerly vertical wind shear. Satellite imagery and reports from an Air Force Reserve Hurricane Hunter aircraft indicate that the circulation has been losing definition during the day and it is now barely closed, at best. However, clusters of strong convection continue in the eastern semicircle, and the initial intensity is held at 45 kt on the premise that the strong winds observed earlier are still present. The central pressure of 1009 mb is based on observations from the Dominican Republic. Erika has been moving more westward for the past several hours and the initial motion is 280/17. There is no change to the forecast philosophy from the previous advisory. A generally west- northwestward to 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. While the track guidance is generally in good agreement, it should be noted that the guidance has been consistently forecasting a west-northwestward turn that has so far failed to occur. On the other hand, there is still a chance for a center to re-form farther to the north during the passage over Hispaniola. So while the forecast track has been shifted west of the previous advisory, it still lies near the northern edge of the guidance envelope for the first 48 hours to maintain some continuity with the previous forecast. Additional adjustments may be necessary depending on how Erika evolves during the next 12-18 hours. The forecast intensity has been significantly changed to show a much weaker cyclone, with Erika now forecast to become a tropical depression in about 24 hours, followed by some slight intensification at 48 and 72 hours. This represents a compromise between two scenarios. The first is the increasing likelihood that Erika will degenerate to a tropical wave during the passage over Hispaniola, a scenario supported by the GFS, UKMET, and ECMWF models. The second acknowledges that the shear is still expected to subside after 36 hours and we're are not quite prepared to rule out tropical storm impacts in Florida. The SHIPS and LGEM support this possibility. 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. Although this would normally be an appropriate time for a tropical storm watch for portions of southern Florida, following typical timelines, we have elected to wait until we see what's left of Erika after it passes Hispaniola. There is a significant chance that no watches or warnings for Florida will be required. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 17.9N 71.2W 45 KT 50 MPH 12H 29/0600Z 19.5N 73.5W 40 KT 45 MPH 24H 29/1800Z 21.3N 76.5W 30 KT 35 MPH...INLAND 36H 30/0600Z 22.7N 79.3W 30 KT 35 MPH...OVER WATER 48H 30/1800Z 24.0N 81.0W 35 KT 40 MPH 72H 31/1800Z 27.0N 82.5W 35 KT 40 MPH 96H 01/1800Z 29.0N 82.5W 30 KT 35 MPH...INLAND 120H 02/1800Z 31.0N 82.5W 25 KT 30 MPH...INLAND $$ Forecaster Beven |
