[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT44 KNHC 292044
TCDAT4

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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