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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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