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Tropical Storm Dorian Discussion Number  13...Corrected
NWS National Hurricane Center Miami FL       AL052019
1100 AM AST Tue Aug 27 2019

Corrected southeastward to southwestward motion in third paragraph

Dorian moved directly across the center of St. Lucia around 1000
UTC, which resulted in a significant disruption of the small
inner-core wind field. An Air Force Reserve reconnaissance aircraft
had difficulty identifying a clear-cut center and radar data from
Martinique indicates that the mid-level circulation has also been
disrupted somewhat. Having said that, the overall appearance
of the cyclone in both satellite and radar imagery has improved
since this time yesterday, although a pronounced dry slot is now
evident in the southeastern quadrant of the circulation. The
initial intensity of 45 kt is being maintained based on aircraft
flight-level and SFMR surface wind data.

The initial motion remains west-northwestward or 295/11 kt. There
is still no significant change to the previous forecast track or
reasoning. Although the inner-core wind field and low-level center
have been disrupted, the overall circulation envelope has remained
intact and is expected to move west-northwestward to northwestward
for the next 36-48 hours toward a break in the subtropical ridge
located well north of Dorian. The mid- to upper-level low currently
located east of the Bahamas that has weakened the ridge is forecast
to gradually weaken while digging southwestward across the central
Bahamas and toward central Cuba over the next 3-4 days, resulting in
Dorian turning northwestward on day 3 before turning back toward the
west-northwest on days 4 and 5. How quickly the west-northwestward
turn occurs will depend heavily on the evolution of the upper-low.
For now, the previous forecast track remains unchanged other than to
push out the track a little northeastward at 48 and 72 hours. The
NHC model guidance remains tightly packed and in good agreement on
this scenario, and the new forecast track lies very close to an
average of the various consensus track models. Users are reminded
not to focus on the details of the extended track forecast as the
average 5-day track error is around 200 miles.

Dry air continues to plague Dorian, and interaction with the
mountainous terrain of St. Lucia will likely hinder significant
development in the short term. However, the models continue to
indicate that the upper-level flow pattern and shear conditions are
expected to remain favorable for strengthening throughout the
forecast period, so it is uncertain why the dynamical models are not
showing more development and strengthening when compared to the more
robust statistical SHIPS intensity models, especially at days 4 and
5 when Dorian will be moving over SSTs greater than 29 deg C and
into a fairly moist environment. For now, the official intensity
forecast remains basically midway between the stronger SHIPS model
and the much weaker global and regional models. Given the large
spread in the guidance, there is lower than normal confidence in the
intensity forecast, especially on days 4 an 5.

Key Messages:

1. Tropical storm conditions will continue in portions of the Lesser
Antilles during the next several hours. Tropical storm conditions
are expected and hurricane conditions are possible in Puerto Rico on
Wednesday and in portions of the Dominican Republic Wednesday night
and Thursday.

2. Heavy rainfall over portions of the Lesser Antilles, Puerto Rico,
and the Dominican Republic could produce flash flooding during the
next few days.

3. The threat of winds and heavy rains later this week into this
weekend in the Turks and Caicos, the Bahamas, and Florida is
increasing. Residents in these areas should monitor the progress of
Dorian and ensure that they have their hurricane plan in place.

4. Uncertainty in the intensity forecast later this week remains
higher than usual due Dorian's potential interaction with Hispaniola
and Puerto Rico.

FORECAST POSITIONS AND MAX WINDS

INIT  27/1500Z 14.2N  61.8W   45 KT  50 MPH
 12H  28/0000Z 15.2N  63.4W   50 KT  60 MPH
 24H  28/1200Z 16.5N  65.5W   55 KT  65 MPH
 36H  29/0000Z 17.9N  67.4W   60 KT  70 MPH
 48H  29/1200Z 19.5N  69.0W   60 KT  70 MPH
 72H  30/1200Z 22.8N  72.0W   55 KT  65 MPH
 96H  31/1200Z 25.6N  76.0W   60 KT  70 MPH
120H  01/1200Z 27.8N  80.4W   60 KT  70 MPH

$$
Forecaster Stewart

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