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#1013022 (Received by flhurricane at: 5:00 PM 20.Aug.2020)
TCDAT3

Tropical Depression Thirteen Discussion Number 4
NWS National Hurricane Center Miami FL AL132020
500 PM AST Thu Aug 20 2020

Recent late afternoon visible satellite imagery has shown evidence
of a low-level swirl that is racing away from the persistent area
of deep convection. It is unclear if that is the only center of
circulation or a swirl rotating around the broader circulation.
The initial position for this advisory is a compromise between the
earlier estimated center location and the swirl seen in satellite
imagery. The initial intensity has been held at 30 kt, based on
the earlier ASCAT data.

The initial motion estimate is a somewhat uncertain 290/18 kt. The
cyclone is located south of a subtropical ridge that is forecast to
build westward over the western Atlantic through early next week.
This ridge should steer the system west-northwestward over the next
several days, and the suite of dynamical track models continue to be
agreement on this overall scenario. The lastest NHC track foreast
is similar to the previous advisory and again lies between the HFIP
corrected consensus and the TVCA multi-model consensus. It should
be noted that since the system is still lacking in organization,
there could be some center reformations that result in some shifts
in the track forecast.

Although the depression has changed little in strength since it
formed yesterday, the overall environment ahead of the system
favors gradual strengthening. The cyclone is forecast to remain
over warm water and in an area of light to moderate vertical wind
shear. Most of the guidance suggests a little more favorable
upper-level wind pattern once the system is north of the Greater
Antilles, but a track farther south would result in more land
interaction, which increases the intensity forecast uncertainty.
The updated NHC intensity forecast shows a slightly slower rate of
strengthening over the next couple of days, but is unchanged at the
latter periods. The overall confidence in both the track and
intensity forecasts remain lower than normal.

Key Messages:

1. Tropical storm conditions are possible across portions of the
northern Leeward Islands, the Virgin Islands, and Puerto Rico
Friday night and Saturday, and Tropical Storm Watches have been
issued for some of these islands. Heavy rainfall is likely across
this area beginning late Friday and could cause mudslides and flash
and urban flooding through Sunday.

2. The details of the long-range track and intensity forecasts are
more uncertain than usual since the system could move over portions
of the Greater Antilles this weekend. However, this system could
bring some storm surge, rainfall and wind impacts to portions of
Hispaniola, Cuba, the Bahamas, and Florida this weekend and early
next week. Interests there should monitor this system`s progress
and updates to the forecast over the next few days.

FORECAST POSITIONS AND MAX WINDS

INIT 20/2100Z 16.7N 53.9W 30 KT 35 MPH
12H 21/0600Z 17.5N 57.2W 30 KT 35 MPH
24H 21/1800Z 18.3N 60.5W 35 KT 40 MPH
36H 22/0600Z 19.1N 63.5W 40 KT 45 MPH
48H 22/1800Z 20.0N 66.7W 45 KT 50 MPH
60H 23/0600Z 20.9N 70.4W 50 KT 60 MPH
72H 23/1800Z 22.2N 74.1W 60 KT 70 MPH
96H 24/1800Z 25.1N 80.4W 65 KT 75 MPH
120H 25/1800Z 28.3N 84.2W 65 KT 75 MPH

$$
Forecaster Brown