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Tropical Storm Dorian Forecast Discussion Number 5
2019-08-25 16:49:27| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Sun Aug 25 2019 000 WTNT45 KNHC 251449 TCDAT5 Tropical Storm Dorian Discussion Number 5 NWS National Hurricane Center Miami FL AL052019 1100 AM AST Sun Aug 25 2019 The convective organization of Dorian has improved a little since the last advisory, as a more persistent area of central convection has formed along with increased, but ragged, outer banding. However, the various satellite intensity estimates remain clustered around 35 kt, and that remains the initial intensity. A combination of 1-minute GOES-16 visible imagery and microwave satellite data have helped pinpoint the center, and the initial motion is 280/12. The subtropical ridge to the north of the cyclone should steer it generally westward to west-northwestward for the next 3-4 days, with a more northwestward motion possible thereafter as Dorian approaches an upper-level low pressure area forecast to be over the north-central Caribbean. The model guidance continues the previous trend of being south of and a bit faster than the previous runs, and as a result the new forecast track is again shifted a little to the south. The new forecast lies between the previous forecast and the various consensus models. However, it is south of the forecasts of the HWRF, the UKMET, and the UKMET Ensemble mean. Additional adjustments to the track may be required on the next advisory if the current model trends continue. While vertical wind shear is decreasing over Dorian, the cyclone still appears to be ingesting dry air based on the ragged convective pattern. Some dry air entrainment is expected to continue for the next few days, and based on this the new intensity forecast again calls for gradual strengthening through 72 h. This part of the intensity forecast is in best agreement with the SHIPS model, and it lies near the upper edge of the intensity guidance. The intensity forecast becomes low confidence after 72 h due to uncertainties in the amount of shear and land that Dorian will encounter. The new forecast calls for some weakening due to shear before Dorian moves over Hispaniola, followed by weakening to a depression due to passage over the island. However, the large range of possibilities includes both Dorian going north of Hispaniola and remaining a hurricane and the small cyclone dissipating completely over Hispaniola. Key Messages: 1. A Tropical Storm Warning has been issued for Barbados, and a Tropical Storm Watch is in effect for St. Lucia, St. Vincent, and the Grenadines. Additional watches and warnings for other portions of the Lesser Antilles could be required later today. 2. It is too soon to determine the specific timing or magnitude of impacts in Puerto Rico, the Virgin Islands, or Hispaniola, but interests in those areas should monitor the progress of Dorian. FORECAST POSITIONS AND MAX WINDS INIT 25/1500Z 11.2N 52.9W 35 KT 40 MPH 12H 26/0000Z 11.5N 54.6W 40 KT 45 MPH 24H 26/1200Z 12.0N 56.9W 45 KT 50 MPH 36H 27/0000Z 12.7N 59.1W 50 KT 60 MPH 48H 27/1200Z 13.5N 61.2W 55 KT 65 MPH 72H 28/1200Z 15.6N 65.3W 65 KT 75 MPH 96H 29/1200Z 17.5N 69.0W 60 KT 70 MPH 120H 30/1200Z 20.0N 72.0W 25 KT 30 MPH $$ Forecaster Beven
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