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| #798503 (Received by flhurricane at: 4:52 PM 26.Aug.2015) TCDAT5 TROPICAL STORM ERIKA DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052015 500 PM AST WED AUG 26 2015 The satellite presentation of the tropical storm has become less organized since the previous advisory, with the low-level center becoming exposed to the northwest of the thunderstorm activity. A NOAA Hurricane Hunter aircraft investigating Erika this afternoon has not found flight-level or SFMR winds as strong as reported this morning, but the aircraft did not sample much of the eastern portion of the circulation. The initial intensity is held at 40 kt, but this could be generous. The intensity forecast philosophy has not changed since this morning. Erika is forecast to move through an area of moderate to strong westerly shear during the next two to three days. Although the NHC intensity forecast during that time shows no change in intensity, weakening is possible during the next couple of days. In fact, Erika could degenerate into a trough of low pressure due to the shear and interaction with the Greater Antilles. After 72 hours, the upper-level environment is forecast to become more conducive for development and all of the guidance, including the global models, shows intensification. Therefore, the days 4 and 5 intensity forecast again calls for strengthening, but is below the intensity consensus and near the SHIPS model. The official forecast leans toward the lower side of the guidance to reflect the possibility that the cyclone's structure would be too disrupted to fully take advantage of the more conducive environment late in the period. The initial motion remains 280/15 kt. Erika is forecast to move west-northwestward during the next three to four days to the south of a subtropical ridge over the western Atlantic. After that time, the global models show a weakness in the ridge developing over the far western Atlantic, which should cause Erika to turn northwestward. All of the models have shifted eastward at days four and five, but the normally reliable GFS and ECMWF define the western edge of the guidance. Out of respect of these models and the previous NHC forecast, the updated track has only been moved slightly eastward late in the period. As a result, the new forecast lies west of the multi-model consensus at 96 and 120 h. One should remember to not focus on the exact forecast track, especially at the long range where the average NHC track errors during the past 5 years are about 180 miles at day 4 and 240 miles at day 5. FORECAST POSITIONS AND MAX WINDS INIT 26/2100Z 16.6N 58.9W 40 KT 45 MPH 12H 27/0600Z 17.1N 61.2W 40 KT 45 MPH 24H 27/1800Z 18.1N 64.0W 40 KT 45 MPH 36H 28/0600Z 19.2N 66.8W 40 KT 45 MPH 48H 28/1800Z 20.5N 69.6W 40 KT 45 MPH 72H 29/1800Z 22.7N 74.3W 40 KT 45 MPH 96H 30/1800Z 25.0N 77.7W 55 KT 65 MPH 120H 31/1800Z 27.5N 80.0W 65 KT 75 MPH $$ Forecaster Brown |
