Official Discussion issued by the National Hurricane Center

(AL092020) DATA RELEASED: 7/29/2020 3:00:00 PM UTC

Copy of official data

Potential Tropical Cyclone Nine Discussion Number   5
NWS National Hurricane Center Miami FL       AL092020
1100 AM AST Wed Jul 29 2020

Surface observations from the Lesser Antilles show that the broader 
circulation of the disturbance has become slightly better defined 
but a recent Air Force Reserve reconnaissance aircraft was still 
unable to find a well-defined circulation.  Therefore, the system 
has not yet become a tropical cyclone.  The aircraft measured peak 
flight-level winds of 46 kt and several SFMR winds of around 35 kt, 
so the initial intensity remains 40 kt for this advisory.

The system continues moving briskly west-northwestward at 290/20 kt. 
The forecast reasoning remains unchanged as a ridge to the north of 
the system is expected to steer the disturbance west-northwestward 
during the next couple of days.  This motion should bring the system 
near or over Hispaniola on Thursday and near eastern Cuba Thursday 
night and Friday.  The ridge is forecast to weaken by the weekend 
which should cause a reduction in forward speed. It still must be 
stressed that since the system lacks a well-defined center and 
remains in its formative stage, uncertainty in the specifics of the 
track forecast remain high in both the short and longer range.  The 
latest NHC track foreast has been nudged slightly south of the 
previous advisory and lies between the latest ECMWF solution and the 
various consensus aids. 

Deep convection has consolidated and there is some evidence of 
banding over the northern and western portions of the large 
circulation.  As a result, the system is still expected to  become a 
tropical storm later today or tonight.  Some additional 
intensification is then possible before the system reaches 
Hispaniola on Thursday, but weakening is likely to occur while it 
interacts with land.  After that time, the system's close proximity 
to eastern Cuba and an expected increase in southwesterly shear are 
likely to inhibit significant re-strengthening.  The latest NHC 
wind speed forecast has been lowered from the previous advisory at 
72-120 h.  Given the expected land interaction and less than ideal 
upper-level environment it is best to remain conservative at this 
time. 

Interests in Hispaniola, the Bahamas, Cuba, and Florida should 
continue to monitor forecasts as changes to both the track and 
intensity are likely.

Key Messages:

1. Potential Tropical Cyclone Nine will produce heavy rains and 
potentially life-threatening flash flooding and mudslides across
the northern Leeward Islands, the Virgin Islands, Puerto Rico, and
the Dominican Republic.

2. Tropical storm conditions are likely across portions of the 
Leeward Islands, the Virgin Islands, and Puerto Rico today and will 
spread westward to portions of the Dominican Republic, Haiti, and 
the southeastern Bahamas and Turks and Caicos on Thursday and 
Thursday night. Tropical Storm Warnings are in effect for these 
areas. Do not focus on the details of the track forecast, as 
rainfall and wind hazards will extend far from the center of the 
system.

3. The details of the long-range track and intensity forecasts 
remain more uncertain than usual since the system does not have a
well-defined center and it is expected to move near or over portions
of the Greater Antilles later this week. However, this system could 
bring some rainfall and wind impacts to portions of Cuba, the 
central and northwest Bahamas, and Florida later this week and this 
weekend. Interests there should monitor its progress and updates to 
the forecast over the next few days.

FORECAST POSITIONS AND MAX WINDS

INIT  29/1500Z 15.8N  63.7W   40 KT  45 MPH...POTENTIAL TROP CYCLONE
12H  30/0000Z 16.9N  66.4W   45 KT  50 MPH...TROPICAL CYCLONE
24H  30/1200Z 18.5N  69.8W   50 KT  60 MPH
36H  31/0000Z 19.9N  73.0W   40 KT  45 MPH...INLAND
48H  31/1200Z 21.4N  76.0W   40 KT  45 MPH...NEAR COAST
60H  01/0000Z 22.7N  78.3W   40 KT  45 MPH...OVER WATER
72H  01/1200Z 23.8N  80.2W   45 KT  50 MPH
96H  02/1200Z 26.3N  82.6W   45 KT  50 MPH
120H  03/1200Z 29.0N  83.5W   45 KT  50 MPH

$$
Forecaster Brown