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Potential Tropical Cyclone NINE (Text)


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Potential Tropical Cyclone Nine Discussion Number   6
NWS National Hurricane Center Miami FL       AL092020
500 PM AST Wed Jul 29 2020
 
Deep convection has continued to increase in association with the
disturbance since the previous advisory.  More recently, a band has
developed over the southwestern portion of the broad circulation
and it appears that the system may be closer to acquiring a
well-defined center.  Earlier ASCAT data that arrived shortly after
the release of the previous advisory revealed a large area of 35-40
kt winds well to the north of the vorticity maximum.  This
supports maintaining the initial intensity of 40 kt.
 
The estimated motion remains a brisk 290/20 kt.  A strong 
subtropical ridge that extends westward over the western Atlantic 
should continue to steer the system west-northwestward over the next 
couple of days, bringing the system near or over Hispaniola late 
tonight and Thursday.  A mid-latitude trough moving into the central 
United States on Friday is foreast to weaken the western portion of 
the ridge which should cause a reduction in the forward speed of the 
system and a turn toward the northwest and north later in the 
forecast period.  The latest iterations of the dynamical models have 
trended toward a more eastward solution, taking the system near or 
just east of the Florida peninsula.  Since the system still lacks a 
well-defined center it is not surprising to see these 
inconsistencies in the model runs.  As a result, the NHC forecast 
has been shifted eastward, but it remains to the west of the latest 
multi-model consensus aids out of respect for continuity and the 
continued possibility of further model shifts. 
 
The system is still forecast to become a tropical storm before
reaching Hispaniola, and some slight strengthening could occur
before landfall Thursday morning.  Some weakening is likely as the 
system moves over that island.  The system is likely to take some 
time to recover after its passage over land, and given the forecast 
for at least moderate south to southwesterly shear, only 
gradual strengthening is indicated at that time.  As mentioned 
above, some of the global models are now showing a track farther 
away from eastern Cuba and east of Florida, and if that occurs the 
NHC intensity forecast could be somewhat conservative.  Interests 
in 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, the Dominican Republic, northern Haiti, and over the 
Inagua Islands into the southeastern Bahamas.

2. Tropical storm conditions are likely across portions of the
Leeward Islands, the Virgin Islands, and Puerto Rico through 
tonight 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 and move near or over 
Florida this weekend.  While 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, it is too 
soon to determine the location or magnitude of those impacts. 
Interests there should monitor the progress of this system and 
updates to the forecast over the next few days.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  29/2100Z 16.4N  65.6W   40 KT  45 MPH...POTENTIAL TROP CYCLONE
 12H  30/0600Z 17.5N  68.1W   45 KT  50 MPH...TROPICAL CYCLONE
 24H  30/1800Z 19.2N  71.0W   40 KT  45 MPH...INLAND
 36H  31/0600Z 20.9N  74.2W   40 KT  45 MPH...OVER WATER
 48H  31/1800Z 22.3N  76.9W   45 KT  50 MPH
 60H  01/0600Z 23.6N  78.9W   50 KT  60 MPH
 72H  01/1800Z 25.5N  80.8W   45 KT  50 MPH...INLAND
 96H  02/1800Z 28.6N  82.1W   40 KT  45 MPH...INLAND
120H  03/1800Z 31.5N  82.5W   35 KT  40 MPH...INLAND
 
$$
Forecaster Brown
 
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Page last modified: Thursday, 22-Oct-2020 12:09:23 UTC