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| #798356 (Received by flhurricane at: 4:43 AM 26.Aug.2015) TCDAT5 TROPICAL STORM ERIKA DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052015 500 AM AST WED AUG 26 2015 Convection has increased near and to the east of the estimated center position of Erika during the past few hours. Subjective and objective Dvorak estimates remain T2.5/35 kt, and that is the intensity for this advisory. The central pressure of 1003 mb is based on a dropsonde from a NOAA aircraft that reported 1004 mb and 25 kt of wind south of the apparent surface center. The intensity forecast remains very uncertain. Despite the recent improvement in the convective pattern, the statistical guidance shows only very gradual strengthening during the forecast period due to 15 to 25 kt of westerly to northwesterly shear. Another major negative factor in the SHIPS model is the weakening of the vortex in the GFS forecast. The HWRF is also very slow to strengthen Erika in the short term, but continues to show intensification late in the period. The latest ECMWF run shows a more robust cyclone in its latest forecast, while the GFS, as mentioned above, weakens the vortex to a wave in 2 to 3 days. Given this uncertainty, the NHC forecast remains close to the intensity consensus and shows very slow intensification in the first 2 to 3 days followed by steadier strengthening at days 4 and 5. The initial motion estimate is 280/16. Erika will be steered westward to west-northwestward over the next 2 to 3 days by the Atlantic subtropical ridge to the north, and the track model guidance is in good agreement on this scenario. After that time, the track model guidance shows increasing spread with a lack of run to run consistency. For example, the latest run of the GFS takes a much weaker Erika west-northwestward while the new ECMWF run is stronger with Erika with a track farther to the right. Overall, the track guidance envelop has shifted a little to the left this cycle, with the majority of the aids showing a west-northwestward to northwestward motion as the cyclone nears the western edge of the ridge by day 5. The NHC forecast follows this trend and is close to the HWRF and a little to the right of the ECMWF and GEFS ensemble mean at days 3 through 5. This track is left of the TVCA consensus, which has been pulled to the right by the outlier GFDL model this cycle. Given the uncertainty, this is a good time to remind users that average NHC track forecast errors over the past 5 years are 180 miles at day 4 and 240 miles at day 5. New tropical storm warnings have been issued for Puerto Rico, the Virgin Islands, and several other islands in the northeastern Caribbean by their respective Meteorological Services. FORECAST POSITIONS AND MAX WINDS INIT 26/0900Z 16.1N 56.0W 35 KT 40 MPH 12H 26/1800Z 16.5N 58.4W 40 KT 45 MPH 24H 27/0600Z 17.2N 61.5W 40 KT 45 MPH 36H 27/1800Z 18.1N 64.5W 45 KT 50 MPH 48H 28/0600Z 19.2N 67.2W 45 KT 50 MPH 72H 29/0600Z 21.4N 72.4W 50 KT 60 MPH 96H 30/0600Z 24.0N 76.5W 60 KT 70 MPH 120H 31/0600Z 26.0N 79.5W 70 KT 80 MPH $$ Forecaster Brennan |
