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Hurricane Dorian Discussion Number 56
NWS National Hurricane Center Miami FL AL052019
500 AM AST Sat Sep 07 2019
Dorian is gradually becoming less organized. The cyclone is feeling
some effects of southwesterly wind shear with most of its deep
convection located to the north and east of the estimated center.
The initial intensity is lowered a little to 75 kt, which is in good
agreement with the latest Dvorak CI-numbers from TAFB and SAB. A
pair of ASCAT passes from several hours ago indicate that the wind
field has expanded significantly, and tropical-storm-force winds
have been observed over far southeastern Massachusetts.
Dorian is racing northeastward, with the latest initial motion
estimated to be 050/22 kt. The hurricane is well embedded in the
fast mid-latitude flow, and it should continue to move quickly
northeastward toward Nova Scotia later today. After the cyclone
passes Nova Scotia, it is forecast to move through Newfoundland and
Labrador before turning east-northeastward over the far north
Atlantic. The NHC track forecast is largely an update of the
previous one and not far from the various consensus aids.
Dorian is expected to gradually weaken due to even stronger
southwesterly wind shear and much colder SSTs to the north of
the Gulf Stream current. The combined influences of these cold
waters and an approaching mid- to upper-level trough should cause
Dorian to lose its tropical characteristics in about 24 hours.
However, the post-tropical cyclone will likely still be producing
hurricane-force winds as it moves through portions of eastern
Canada. The global models are in good agreement that the
post-tropical cyclone should slowly weaken and ultimately become
absorbed by another extratropical low in 3 to 4 days. The NHC
intensity forecast is in best agreement with the GFS and ECMWF
models, which typically handle large extratropical lows better that
than the intensity models that are made for tropical cyclones.
1. Regardless of whether it is a hurricane or a post-tropical
cyclone, Dorian is expected to have a significant impact in portions
of eastern Canada beginning later today. Dangerous storm surge
impacts are likely in portions of the Gulf of St. Lawrence,
southwestern Newfoundland and eastern Nova Scotia. Hurricane-force
winds are also likely in Nova Scotia, Prince Edward Island and
Newfoundland later today and tonight. Refer to information from the
Canadian Hurricane Centre for more information on these hazards.
FORECAST POSITIONS AND MAX WINDS
INIT 07/0900Z 39.7N 68.1W 75 KT 85 MPH
12H 07/1800Z 42.8N 64.9W 70 KT 80 MPH
24H 08/0600Z 46.9N 61.6W 65 KT 75 MPH...POST-TROP/EXTRATROP
36H 08/1800Z 50.0N 58.0W 55 KT 65 MPH...POST-TROP/EXTRATROP
48H 09/0600Z 52.5N 52.0W 45 KT 50 MPH...POST-TROP/EXTRATROP
72H 10/0600Z 57.5N 36.0W 40 KT 45 MPH...POST-TROP/EXTRATROP