[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT42 KNHC 240240
TCDAT2

Tropical Storm Gonzalo Discussion Number  10
NWS National Hurricane Center Miami FL       AL072020
1100 PM AST Thu Jul 23 2020

After ingesting a hefty portion of dry high statically stable air
this morning, Gonzalo appears to be on the comeback trail.
Enhanced infrared BD-curve imagery shows that a small Central Dense
Overcast with cloud tops of -80C is redeveloping over the surface
center.  A compromise of the available subjective and objective
satellite intensity estimates supports maintaining 50 kt for this
advisory.

This morning's upper air sounding from Barbados revealed a very
dry, high statically stable atmosphere with a mean RH of 23 percent
and a CAPE of only 327 J/Kg.  Consequently, Gonzalo will be moving
into a rather harsh thermodynamic environment over the weekend.  As
a result, the NHC forecast calls for weakening beyond the 48 hour
period as it enters the eastern Caribbean sea and dissipation well
south of Hispaniola at day 5, or sooner as a few of the global
models suggest.  The intensity forecast is basically an update of
the previous advisory through 48 hours, indicating a hurricane
approaching and moving over the southern Windward Islands, and a
faster weakening trend beyond day 2, similar to a consensus of the
large-scale models.

The initial motion is estimated to be westward, or 275/12 kt
within the stiff mid-tropospheric steering flow provided by an
anchored subtropical ridge to the cyclone's north.  The song
remains the same, with Gonzalo expected to speed up toward the west
and west-northwest through the entire period.  The NHC official
forecast is based on a blend of the various consensus aids and is
down the middle of the tightly clustered guidance.

Key Messages

1. The risk of wind and rain impacts from Gonzalo in portions of
the southern Windward Islands this weekend continues to increase,
however there is significant uncertainty in how strong Gonzalo will
be when it moves across the islands.

2. Despite the uncertainty in Gonzalo's future intensity, hurricane
or tropical storm conditions are possible across portions of the
southern Windward Islands Saturday and Saturday night.  Hurricane
and Tropical Storm Watches are currently in effect for some of
the islands, and additional watches or warnings could be required
tonight or early Friday.  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  24/0300Z  9.9N  50.6W   50 KT  60 MPH
 12H  24/1200Z 10.2N  52.5W   55 KT  65 MPH
 24H  25/0000Z 10.7N  55.1W   60 KT  70 MPH
 36H  25/1200Z 11.5N  58.2W   65 KT  75 MPH
 48H  26/0000Z 12.3N  61.3W   65 KT  75 MPH
 60H  26/1200Z 13.3N  64.4W   55 KT  65 MPH
 72H  27/0000Z 13.9N  67.3W   45 KT  50 MPH
 96H  28/0000Z 14.4N  73.7W   35 KT  40 MPH
120H  29/0000Z...DISSIPATED

$$
Forecaster Roberts
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