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Tropical Depression Thirteen Discussion Number 2
NWS National Hurricane Center Miami FL AL132020
500 AM AST Thu Aug 20 2020
There has been little change in the organization of Tropical
Depression Thirteen during the past several hours. An area of
ragged but persistent convection continues near the estimated
center position, and there is some outer banding in the southern
semicircle. Dvorak-based satellite intensity estimates have
changed little since the last advisory, so the initial intensity
remains 30 kt.
The initial motion is a somewhat uncertain 295/18. The subtropical
ridge to the north of the cyclone is expected to build westward to
the north of the Greater Antilles during the next several days, and
this should steer the cyclone generally west-northwestward through
the forecast period. The track guidance remains in fairly good
agreement with this scenario, but there remains a spread between
the GFS/UKMET on the south side of the guidance and the
Canadian/HMON on the north side. Overall, the envelope has shifted
a little to the south since the previous advisory and the new
forecast track, which lies just to the north of the consensus
models, is also nudged southward. The new track calls for the
cyclone to pass near the Leeward Islands in 36-48 h, near or north
of Puerto Rico and the Virgin Islands in 48-60 h, and then near or
over Hispaniola and the southeastern Bahamas by 72 h.
Overall, the environment looks generally favorable for
strengthening, with the cyclone expected to encounter light- to
moderate shear during forecast period. However, the guidance
responds to this environment with a wide range of solutions. The
HWRF/HMON forecast the cyclone to intensify into a major hurricane
by 120 h. On the other hand, the GFS and ECMWF show the system
degenerating into an open wave by 120 h. The UKMET and Canadian
models are between these extremes. The weak GFS solution appears
to be due to forecast dry air entrainment, which is a possibility
as satellite imagery suggests Saharan dust not far from the
cyclone. Between these factors and the possibility of land
interaction, the low-confidence intensity forecast is changed
little from the previous advisory.
1. Tropical storm conditions are possible across portions of the
northern Leeward Islands by Friday night, and Tropical Storm Watches
have been issued for some of these islands. Heavy rainfall is
likely across this area beginning late Friday.
2. There is a risk of tropical storm conditions in the Virgin
Islands and Puerto Rico Friday night and Saturday and Tropical
Storm Watches could be required for these islands later today.
Interests there should closely monitor the progress of this system.
3. 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 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 20/0900Z 15.2N 49.8W 30 KT 35 MPH
12H 20/1800Z 16.4N 52.7W 30 KT 35 MPH
24H 21/0600Z 17.5N 56.4W 35 KT 40 MPH
36H 21/1800Z 18.4N 60.2W 40 KT 45 MPH
48H 22/0600Z 19.1N 63.9W 45 KT 50 MPH
60H 22/1800Z 19.8N 67.1W 50 KT 60 MPH
72H 23/0600Z 20.8N 71.0W 55 KT 65 MPH
96H 24/0600Z 23.0N 78.0W 60 KT 70 MPH
120H 25/0600Z 26.0N 83.0W 60 KT 70 MPH