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Tropical Storm Dorian Discussion Number   6
NWS National Hurricane Center Miami FL       AL052019
500 PM AST Sun Aug 25 2019

While still looking a bit ragged, convection has continued to
increase near the center of Dorian since the last advisory, and a
just-received SSMI/S overpass shows a convective band wrapped about
three-quarters of the way around the center.  Various Dvorak-based
objective and subjective satellite intensity estimates are in the
35-45 kt range, while recent microwave-based estimates are in the
45-60 kt range.  Based on these data, the initial intensity is
increased to 45 kt.

The initial motion remains 280/12 kt.  The subtropical ridge to the
north of the cyclone should steer it generally westward to
west-northwestward for the next 72 h or so, 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 has not shifted much since the
previous advisory.  However, some of the normally reliable models
are in disagreement.  The ECMWF and GFS keep Dorian weaker and
farther south, and they are on the left side of the guidance
envelope.  The HWRF and UKMET have more northerly tracks, and
forecast Dorian to pass near Puerto Rico and then near or north of
Hispaniola.  The various consensus models are between these
extremes, and the earlier forecast is now close to them.  Thus, the
new forecast track is little changed from the previous forecast, and
it calls for Dorian to move through the Windward Islands between
36-48 h and cross Hispaniola between 96-120 h.

Dorian still appears to be ingesting dry air based on the somewhat
ragged convective pattern.  This entrainment is expected to continue
sporadically for the next 2-3 days, and this could slow
intensification despite an environment of light to moderate shear.
The intensity guidance is split on how much intensification could
occur during this time.  The statistical-dynamical SHIPS and LGEM
models showing more intensification and forecast Dorian to become a
hurricane. On the dynamical side, the latest HWRF run shows little
development, and the GFS/ECMWF keep the system weak to the point
where it degenerates into a tropical wave before reaching
Hispaniola.  The intensity forecast follows the general trend of the
statistical-dynamical models, but shows less intensification out of
respect for the dynamical models.  The intensity forecast becomes
even lower confidence after 72 h due to uncertainties in how much
shear and land that Dorian will encounter.  The new forecast calls
for Dorian to weaken to a depression due to passage over Hispaniola.
However, the large range of possibilities also includes both Dorian
going north of Hispaniola and remaining a hurricane and the small
cyclone dissipating completely over the island.

Key Messages:

1. Dorian is expected to bring tropical storm conditions to
portions of the Lesser Antilles, where tropical storm watches and
warnings are in effect.  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 2 to 4 inches of rainfall across
portions of the Lesser Antilles, with isolated amounts as high as 6
inches.

3.  While it is too soon to determine the specific time or
magnitude of possible direct impacts in Puerto Rico, the Virgin
Islands, or Hispaniola interests in those areas should monitor the
progress of Dorian.


FORECAST POSITIONS AND MAX WINDS

INIT  25/2100Z 11.5N  54.2W   45 KT  50 MPH
 12H  26/0600Z 11.8N  55.9W   50 KT  60 MPH
 24H  26/1800Z 12.4N  58.2W   55 KT  65 MPH
 36H  27/0600Z 13.1N  60.3W   55 KT  65 MPH
 48H  27/1800Z 14.1N  62.3W   60 KT  70 MPH
 72H  28/1800Z 16.4N  66.4W   65 KT  75 MPH
 96H  29/1800Z 18.5N  70.0W   60 KT  70 MPH...INLAND
120H  30/1800Z 20.5N  73.0W   25 KT  30 MPH...OVER WATER

$$
Forecaster Beven

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