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Tropical Storm Dorian Discussion Number   9
NWS National Hurricane Center Miami FL       AL052019
1100 AM AST Mon Aug 26 2019

Satellite imagery indicates that Dorian's convective and outflow
pattern have continued to improve, with a narrow poleward outflow
channel now apparent in water vapor images. Passive microwave
imagery has shown a persistent low-level eye-like feature
along with an intermittent mid-level eyewall forming that quickly
erodes due to mid-level dry air entrainment. The initial intensity
of 50 kt is based on a blend of satellite intensity estimates
ranging from 45 kt to 56 kt from TAFB, SAB, and UW-CIMSS ADT and
SATCON.

The initial motion is now west-northwestward or 285/12 kt. Dorian is
expected to continue moving west-northwestward today through Tuesday
night as the cyclone moves around the southwestern periphery of a
deep-layer subtropical ridge situated to its north. On Wednesday,
Dorian is forecast to turn northwestward toward a weakness in the
ridge, which could allow the cyclone to pass near or between
western Puerto Rico and the eastern Dominican Republic. By late
Thursday and Friday, all of the model guidance indicates that the
ridge will build back as an upper-level trough/low weakens and lifts
out to the north, which should result in Dorian turning back toward
the west-northwest in the vicinity of the Bahamas. The new NHC track
forecast has been nudged slightly to the right or north of the
previous one and lies close to the tightly clustered consensus
models HCCA, FSSE, TVCN, and TVCX.

The intensity forecast is less straight-forward than the track
forecast. Environmental conditions, except for the abundance of dry
mid-level air surrounding and occasionally being entrained into
Dorian's inner-core region, would favor at least steady
strengthening due to very low vertical wind shear, SSTs of at least
29C, and the small overall circulation and inner-core wind field.
The recent development of a poleward outflow channel and possible
development of an equatorward channel would also support
strengthening. However, until Dorian closes off a solid eyewall,
only slow strengthening is likely. Anticipating when an eye will
form is challenging, but Dorian could be a hurricane by the time it
reaches the Windward Islands. The intensity forecast has been
adjusted upward form the previous advisory, but is not as high as
the statistical-dynamical SHIPS and LGEM intensity models.
Interaction with Hispaniola and possibly Puerto Rico should result
in some weakening in 72-96 hours, followed by restrengthening on day
5 when Dorian will be moving over the very warm waters in the
Bahamas in low shear conditions. Given the unknown degree of
interaction with Hispaniola, the intensity forecast at days 4 and 5
is of very low confidence.

Key Messages:

1. Dorian is expected to bring tropical storm conditions to portions
of the Lesser Antilles tonight and Tuesday, where tropical storm
watches and warnings are in effect. Hurricane conditions are also
possible in portions of the Windward Islands, and a hurricane watch
has been issued for St. Lucia. Residents in these areas should refer
to advice from local government officials and products from their
local meteorological service for additional information.

2. Dorian is expected to produce 3 to 8 inches of rainfall from
Martinique to St. Vincent, including Barbados, with isolated totals
as high as 10 inches in portions of the northern Windward Islands.

3.  The risk of direct impacts from wind and rainfall has increased
for Puerto Rico and Hispaniola. Interests in those areas should
monitor the progress of Dorian and tropical storm or hurricane
watches will likely be required later today.

4. Any potential impacts from Dorian in the Bahamas and Florida
later this week are highly uncertain, given the potential for the
system to interact with the high terrain of Hispaniola.

FORECAST POSITIONS AND MAX WINDS

INIT  26/1500Z 12.3N  57.7W   50 KT  60 MPH
 12H  27/0000Z 12.9N  59.4W   55 KT  65 MPH
 24H  27/1200Z 13.9N  61.4W   60 KT  70 MPH
 36H  28/0000Z 15.1N  63.5W   65 KT  75 MPH
 48H  28/1200Z 16.4N  65.6W   70 KT  80 MPH
 72H  29/1200Z 19.2N  69.3W   70 KT  80 MPH...NERN HISPANIOLA
 96H  30/1200Z 22.0N  72.6W   40 KT  45 MPH
120H  31/1200Z 24.8N  76.5W   45 KT  50 MPH

$$
Forecaster Stewart

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