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Tropical Storm MATTHEW Forecast Discussion Number 4
2016-09-29 11:05:32| National Hurricane Center (Atlantic)
Issued at 500 AM AST THU SEP 29 2016 000 WTNT44 KNHC 290905 TCDAT4 TROPICAL STORM MATTHEW DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142016 500 AM AST THU SEP 29 2016 Matthew is currently experiencing 15-20 kt of southwesterly vertical wind shear, with the low-level center located near the western edge of the main convective mass. An earlier Air Force Reserve Hurricane Hunter mission reported 850 mb flight-level winds of 65-70 kt and estimated surface winds of 50-55 kt from the SFMR instrument. Based on these data, the initial intensity remains 55 kt. The aircraft reported a central pressure of 1002 mb on its last pass through the center. The initial motion is 275/14. Matthew is currently on the south side of a low- to mid-level subtropical ridge. This feature should steer the storm westward or even south of west during the next 48 hours. After that time, Matthew is expected to approach the western end of the ridge as a mid- to upper-level trough develops over the Gulf of Mexico. While this combination is expected to cause the cyclone to turn generally northward, there is significant disagreement between the dynamical models on where the turn will occur and how fast Matthew will move northward. The forecast track is in best agreement with the GFS and GFS ensemble mean in bringing the center to eastern Cuba by 120 hours, although it is slower than those models. The Canadian model is a little west of the forecast track. The ECMWF and UKMET are to the east of the forecast track and much slower, bringing the center to the island of Hispaniola. Overall, the new forecast track is nudged a little south of the previous track for the first 72 hours, then is similar to the previous track. Users are reminded that the average NHC track errors at days 4 and 5 are on the order of 180 and 240 miles, respectively. The current shear is likely to gradually diminish during the next 72 hours, and this should allow continued gradual development. After that time, there is also disagreement in the models regarding the forecast shear, with the GFS showing a more favorable pattern than the ECMWF. If the GFS upper-level winds are correct, Matthew could strengthen more than currently forecast as show by the HWRF. However, given the uncertainty, the new intensity forecast is the same as the previous forecast and is in best agreement with the intensity consensus. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 14.0N 64.7W 55 KT 65 MPH 12H 29/1800Z 14.1N 66.7W 60 KT 70 MPH 24H 30/0600Z 14.1N 69.2W 65 KT 75 MPH 36H 30/1800Z 13.9N 70.8W 70 KT 80 MPH 48H 01/0600Z 13.8N 72.2W 75 KT 85 MPH 72H 02/0600Z 14.5N 74.0W 75 KT 85 MPH 96H 03/0600Z 17.5N 75.0W 85 KT 100 MPH 120H 04/0600Z 20.5N 75.5W 80 KT 90 MPH...INLAND $$ Forecaster Beven
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