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#798787 (Received by flhurricane at: 4:41 PM 27.Aug.2015) TCDAT5 TROPICAL STORM ERIKA DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052015 500 PM AST THU AUG 27 2015 The center has been wobbling during the day, but the mean motion is estimated to be 285/13. In the mean, a west-northwestward track to the south of a subtropical ridge is likely to continue for the next couple of days. Later in the forecast period, the cyclone should turn to the right along the southwestern and western periphery of the ridge. There remains considerable spread in the track model guidance at days 3 to 5, partly due to differences in model-predicted intensities at those time frames. The official track forecast is in good agreement with the latest dynamical model consensus. The NOAA Gulfstream-IV is currently conducting a synoptic surveillance mission around Erika to provide the numerical models with a better depiction of the storm's environment. These data will be reflected primarily in the 00Z run of the GFS. Vertical shear is expected to be fairly strong for the next couple of days and that, along with the interaction with land, should preclude significant strengthening for the next 48 hours or so. Beyond that time, the shear is forecast to relax somewhat, and this could allow for intensification assuming that the cyclone is not too disrupted by the mountainous land mass of Hispaniola. Because of the marginal upper-level wind environment and potential interaction with land over the next few days, there is unusually high uncertainty in the forecast intensity, especially at days 3 to 5. The biggest short-term threat posed by Erika is very heavy rainfall over portions of the Leeward Islands, which should spread over the Virgin Islands and Puerto Rico tonight and early Friday. These rains could produce flash floods and mud slides. More than 12 inches of rain has fallen in Dominica, with reports of fatalities in that island. FORECAST POSITIONS AND MAX WINDS INIT 27/2100Z 16.6N 64.0W 40 KT 45 MPH 12H 28/0600Z 17.9N 66.4W 45 KT 50 MPH 24H 28/1800Z 19.2N 69.2W 45 KT 50 MPH 36H 29/0600Z 20.7N 72.0W 45 KT 50 MPH 48H 29/1800Z 22.1N 74.7W 45 KT 50 MPH 72H 30/1800Z 24.9N 78.8W 55 KT 65 MPH 96H 31/1800Z 27.0N 80.0W 65 KT 75 MPH 120H 01/1800Z 29.5N 80.5W 75 KT 85 MPH $$ Forecaster Pasch |