Tropical Storm DORIAN (Text)


Tropical Storm Dorian Discussion Number  14
NWS National Hurricane Center Miami FL       AL052019
500 PM AST Tue Aug 27 2019

Dorian's convective pattern has continued to fluctuate this
afternoon due to some interaction with the Windward and Leeward
Islands, but mainly due to intrusions of very dry mid-level air. A
10-mile wide eye feature developed in Martinique and Guadeloupe
radar data between 1500-1600 UTC and again between 1700-1800 UTC.
But this feature had been short-lived due to erosion of the
inner-core convection caused by dry air entrainment, although a
recent burst of deep convection has developed near and over the
low-level center. Dorian's upper-level outflow has continued to
expand and is very symmetrical. The initial intensity has been
maintained at 45 kt based on earlier aircraft flight-level and SFMR
surface wind data.

Despite the center redeveloping farther north, radar and recon
fixes indicate that the motion remains west-northwestward or
300/11 kt. Due to the more northward initial position, the new
forecast track was shifted 30-60 n mi northeast of the previous
one track through 96 hours. The global models are in good agreement
on Dorian moving west-northwestward tonight and then turning
northwestward on Wednesday, bringing the cyclone's center near
or over the central or western portions of Puerto Rico. After
clearing the island by early Thursday, Dorian is forecast to move
cyclonically around the eastern portion of a southwestward-moving
mid/upper-level low on days 3-5. The evolution of the upper-low and
how strong the mid-level ridge to the north builds in behind the low
and across the southeastern U.S. will determine when and how sharp
Dorian's turn back the west-northwest will occur. The new NHC track
is close to a blend consensus models TVCN, HCCA, and FSSE, and
brings Dorian near the east-central Florida coast in 120 hours.
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 should continue to plague Dorian for the next 24 hours or
so, resulting in only slow strengthening. Land interaction with
Puerto Rico should significantly weaken the small cyclone, thus the
intensities were lowered at 36 and 48 hours. On days 3-5, the models
continue to indicate that the upper-level flow pattern and shear
conditions should favor strengthening, especially since Dorian will
be moving over SSTs greater than 29 deg C and into a moist mid-level
environment. The dynamical models such as the GFS, UKMET, and ECMWF
are now showing more strengthening than previous runs, but still
remain well below the statistical SHIPS and LGEM intensity models,
which bring Dorian to category 1 or 2 strength by day 5. The
official intensity forecast remains a compromise between the these
two extremes, and is close to the HCCA and FSSE consensus models.
Given the large spread in the guidance, there remains lower-than-
normal confidence in the intensity forecast, especially on days 4
and 5.

Key Messages:

1. Tropical storm conditions are expected in the U.S. Virgin Islands
and Puerto Rico on Wednesday and in portions of the Dominican
Republic Wednesday night and Thursday. Hurricane conditions are
possible in Puerto Rico and portions of the Dominican Republic.

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

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


INIT  27/2100Z 15.3N  62.5W   45 KT  50 MPH
 12H  28/0600Z 16.2N  64.1W   50 KT  60 MPH
 24H  28/1800Z 17.6N  66.2W   55 KT  65 MPH
 36H  29/0600Z 19.1N  67.8W   40 KT  45 MPH
 48H  29/1800Z 20.8N  69.2W   45 KT  50 MPH
 72H  30/1800Z 24.2N  72.2W   55 KT  65 MPH
 96H  31/1800Z 26.7N  76.1W   60 KT  70 MPH
120H  01/1800Z 28.2N  80.6W   60 KT  70 MPH...NEAR THE FLORIDA COAST

Forecaster Stewart


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Page last modified: Tuesday, 31-Dec-2019 12:09:13 UTC