[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 230842
TCDAT2

Tropical Storm Gonzalo Discussion Number   7
NWS National Hurricane Center Miami FL       AL072020
500 AM AST Thu Jul 23 2020

A 0441 UTC ATMS/Soumi NPP microwave overpass revealed a
well-developed banding feature wrapping into the center from the
east semi-circle.  Cloud tops have once again cooled near the
surface center and subsequently, the Dvorak satellite intensity
estimates from both TAFB and SAB have increased to T3.5 (55 kt).
Accordingly, the initial intensity is raised to 55 kt for this
advisory.

No major changes were made to the intensity forecast and there
still remains a relatively high degree of uncertainty beyond day 3
while the cyclone moves through the Caribbean Sea.  Strengthening
is forecast through 48 hours as Gonzalo approaches the Islands and
the forecast is close to a blend of the HCCA intensity consensus,
the IVCN multi-model guidance and the Decay SHIPS.  Beyond
mid-period, the forecast reflects a weakening trend in respect to
the European models solution, but at much more gradual rate.  It
should also be noted that the small size of this system makes it
susceptible to significant fluctuations in intensity, both upward
and downward.

The initial motion is estimated to be due west, or 270/10 kt.
The forecast track philosophy remains unchanged. Gonzalo is moving
within low to mid-level easterly steering flow produced by a
subtropical ridge anchored to the north of the cyclone, and this
high pressure should steer the storm generally westward at a faster
forward speed for the next few days.  After that time, a motion
toward  the west-northwest is expected.  Two distinct
model clusters with differing forecast track solutions persist.  The
European models along with the Canadian indicate a weak cyclone
moving generally westward through the southern Windward Islands and
dissipating in 5 days or less.  The NCEP models, on the other hand,
show a much stronger tropical cyclone with a west-northwestward to
northwestward motion toward Hispaniola.  The NHC forecast basically
down the middle of these to model clusters and is very close to the
TVCA consensus aid.

Interests in the Windward Islands should continue to monitor the
progress of this system.  A Hurricane Watch is in effect for
Barbados.


Key Messages

1. There is an increasing risk of wind and rain impacts from
Gonzalo in portions of the southern Windward Islands this weekend.
Hurricane conditions are possible on Barbados where a hurricane
watch has been issued.  Interests in the southern Windward Islands
should monitor the progress of Gonzalo and follow any advice given
by local officials.


FORECAST POSITIONS AND MAX WINDS

INIT  23/0900Z 10.0N  47.0W   55 KT  65 MPH
 12H  23/1800Z 10.1N  48.7W   65 KT  75 MPH
 24H  24/0600Z 10.4N  51.1W   70 KT  80 MPH
 36H  24/1800Z 10.9N  53.9W   75 KT  85 MPH
 48H  25/0600Z 11.5N  57.0W   75 KT  85 MPH
 60H  25/1800Z 12.2N  60.1W   70 KT  80 MPH
 72H  26/0600Z 13.0N  63.1W   65 KT  75 MPH
 96H  27/0600Z 14.8N  68.8W   50 KT  60 MPH
120H  28/0600Z 16.5N  74.5W   40 KT  45 MPH

$$
Forecaster Roberts
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