Tropical Storm Dorian Discussion Number 16
NWS National Hurricane Center Miami FL AL052019
500 AM AST Wed Aug 28 2019

Satellite images and Doppler radar data from Puerto Rico indicate
that Dorian is becoming better organized with banding features now
more established on the north side of the circulation. The
flight-level and SFMR winds from the Air Force Hurricane Hunters
were a little higher in the most recent passes through the storm,
and a blend of that data supports an initial intensity of about 50
kt. The Hurricane Hunters also reported that Dorian has developed a
partial eyewall and that the minimum pressure has dropped to 1003
mb. A combination of the reconnaissance data and recent ASCAT
passes were used to modify the initial wind radii, and it confirms
that Dorian remains a compact and asymmetric tropical storm.

Dorian is moving northwestward at 11 kt toward a weakness in the
ridge caused by a cut off mid- to upper-level low to the north of
Hispaniola. This motion should continue for the next few days,
taking Dorian across the Virgin Islands or the eastern portion of
Puerto Rico later today and to the east of the Bahamas on Thursday
and Friday. By late in the week, the steering pattern is expected
to change as the models show a ridge building over the western
Atlantic. The flow between the ridge and the aforementioned mid- to
upper-level low should cause Dorian to turn west-northwestward and
approach the southeast U.S. coast this weekend. The new NHC
track forecast is adjusted a little to the right at most forecast
times trending toward the latest consensus aids. However, there has
been considerable run-to-run variability among the models so
confidence in the long term track remains low. In addition, users
are reminded not to focus on the exact forecast points as the
average 5-day track error is around 200 miles.

Some additional slow strengthening seems likely today before Dorian
reaches Puerto Rico and the Virgin Islands. The land interaction
could end the strengthening trend or even cause some temporary
weakening, however, environmental conditions favor intensification
after the storm pulls northward into the southwestern Atlantic.
Nearly all of the intensity models show Dorian becoming a hurricane
in about 2 days, with additional strengthening beyond that time.
The NHC intensity forecast is increased from the previous one,
especially at the longer forecast times, to be in better agreement
with the latest models. This forecast, however, is still on the
lower end of the guidance envelope, so additional upward adjustments
could be needed if the guidance trends persists. It is also worth
noting that the global models show Dorian increasing in size by the
time it nears the southeast U.S.


Key Messages:

1. Tropical storm conditions are expected in the U.S. and British
Virgin Islands and Puerto Rico today, and are possible in
portions of the Dominican Republic tonight and Thursday.
Hurricane conditions are possible in Puerto Rico and the U.S.
Virgin Islands today.

2. Heavy rainfall over portions of Puerto Rico and the U.S. and
British Virgin Islands could produce flash flooding during the next
couple of days. Heavy rains are expected to occur over portions of
the Bahamas and Florida later this week and into early next week.

3. The threat of tropical storm or hurricane conditions, along with
storm surge, in the northwestern Bahamas and along portions of the
Florida east coast have increased. 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 late this week remains
higher than usual due to a large spread in the model guidance.


FORECAST POSITIONS AND MAX WINDS

INIT 28/0900Z 16.8N 63.9W 50 KT 60 MPH
12H 28/1800Z 17.9N 65.3W 60 KT 70 MPH
24H 29/0600Z 19.5N 66.8W 60 KT 70 MPH
36H 29/1800Z 21.4N 68.2W 60 KT 70 MPH
48H 30/0600Z 23.3N 69.6W 65 KT 75 MPH
72H 31/0600Z 26.1N 73.0W 80 KT 90 MPH
96H 01/0600Z 27.7N 77.1W 85 KT 100 MPH
120H 02/0600Z 29.0N 80.0W 85 KT 100 MPH