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Hurricane Dorian Forecast Discussion Number 20
2019-08-29 10:43:40| National Hurricane Center (Atlantic)
Issued at 500 AM AST Thu Aug 29 2019 000 WTNT45 KNHC 290843 TCDAT5 Hurricane Dorian Discussion Number 20 NWS National Hurricane Center Miami FL AL052019 500 AM AST Thu Aug 29 2019 Soon after the previous advisory was issued, Dorian appeared to have a bit of a hiccup in its structure. A dry slot was noted penetrating into the southeastern portion of the circulation, with the eye becoming cloud- and rain-filled. In fact, dropsonde data from the Air Force Reserve mission indicated that the central pressure had come back up a bit to around 991 mb. That being said, the plane still measured maximum SFMR winds between 70-75 kt, so the initial intensity is being held steady at 75 kt for this advisory. Dorian continues northwestward, or 325 degrees at 11 kt. Confidence in the track forecast is fairly high for the first 48 hours, with Dorian expected to continue moving northwestward and then begin to turn west-northwestward between mid-level ridging to the north and a mid- to upper-level low retrograding westward across the Straits of Florida. The models, and their ensembles, continue to diverge after 48 hours and have not really budged from their respective solutions compared to yesterday. The GFS is a northern outlier from the rest of the guidance, showing a weaker ridge and bringing Dorian close to the Florida/Georgia border, while the UKMET and ECMWF models show stronger ridges and remain the southernmost solutions near South Florida. Given the spread in the guidance, the new NHC forecast blends the previous forecast with the simple multi-model consensus aids and the HCCA and Florida State Superensemble aids, and it actually ends up in a position very close to the tightly clustered global model ensemble means. The most notable change in the new forecast is that it's a little bit slower than the previous one as Dorian approaches Florida. Various shear analyses are indicating 10-15 kt of southwesterly shear over Dorian at the moment, but the global models show this shear diminishing within 12-24 hours. With lower shear and very warm waters, all of the intensity models forecast Dorian to begin strengthening again soon, and rapid intensification could occur. The updated NHC intensity forecast has been increased from the previous one and most closely follows the HCCA and Florida State Superensemble aids during the first day or two. After 48 hours, the official forecast is near or just above the intensity consensus, but it's still lower than the solutions shown by the HCCA, Florida State Superensemble, and the HWRF. Dorian is likely to reach major hurricane strength in the next day or two and is forecast to maintain that status until it reaches land. Key Messages: 1. The risk of dangerous storm surge and hurricane-force winds later this week and this weekend continues to increase in the central and northwestern Bahamas and along the Florida east coast, although it is too soon to determine where these hazards will occur. Residents in these areas should ensure they have their hurricane plan in place and not focus on the exact forecast track of Dorian's center. 2. Heavy rains are expected to occur over portions of the Bahamas, Florida, and elsewhere in the southeastern United States later this week and into early next week. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 20.5N 66.6W 75 KT 85 MPH 12H 29/1800Z 21.9N 67.6W 85 KT 100 MPH 24H 30/0600Z 23.7N 69.0W 95 KT 110 MPH 36H 30/1800Z 25.1N 70.6W 100 KT 115 MPH 48H 31/0600Z 26.0N 72.5W 105 KT 120 MPH 72H 01/0600Z 27.0N 76.4W 110 KT 125 MPH 96H 02/0600Z 27.5N 79.5W 110 KT 125 MPH 120H 03/0600Z 28.0N 81.5W 75 KT 85 MPH...INLAND $$ Forecaster Berg
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