[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 222032
TCDAT2

Tropical Storm Gonzalo Discussion Number   5
NWS National Hurricane Center Miami FL       AL072020
500 PM AST Wed Jul 22 2020

Satellite imagery suggests that Gonzalo's intensification has
paused since the last advisory.  The cyclone continues to show a
central dense overcast, and microwave imagery indicates a small
convective ring present under the overcast.  However, the CDO has
become a bit ragged, and the other banding seen earlier has
dissipated.  Subjective and objective satellite intensity estimates
are in the 45-55 kt range, the the initial intensity remains a
possibly conservative 45 kt.

The initial motion is now 270/12.  There is no change to the
track forecast philosophy.  Gonzalo is on the south side of a low-
to mid-level subtropical ridge, and this feature should steer the
storm generally westward at a faster forward speed for the next 60
h or so.  After that time, a motion toward the west-northwest is
expected.  The new NHC forecast track is again little changed from
the previous track, and it lies very close to the consensus models.

The intensity forecast remains very problematic and of low
confidence. On one side, the cyclone structure, light shear
environment,and warm sea surface temperatures suggest strengthening,
possibly even rapidly, should occur.  In addition, the SHIPS-based
guidance and the HWRF still make the system a hurricane.  On the
other side, the GFS, UKMET, and ECMWF models continue to forecast
the system to weaken to an open wave by 120 h, possibly due to dry
air entrainment and large-scale subsidence, and microwave imagery
suggests that a tongue of drier air is present west and southwest
of the cyclone.  The NHC intensity forecast again compromises
between these extremes, showing Gonzalo peaking as a hurricane in
36-48 h, followed by weakening in deference to the GFS/UKMET/ECMWF.
The new intensity forecast is unchanged from the previous forecast.
As noted before, the small size of this system makes it
susceptible to significant fluctuations in intensity, both upward
and downward.

Interests in the Windward Islands should monitor the progress of
this system, as watches could be issued sometime on Thursday.


Key Messages

1. Gonzalo is expected to move near or over the southern Windward
Islands this weekend, and could bring direct impacts from winds and
heavy rainfall. While it is too soon to determine the magnitude and
timing of those impacts, interests in the southern Windward Islands
should monitor the progress of Gonzalo.


FORECAST POSITIONS AND MAX WINDS

INIT  22/2100Z  9.9N  45.0W   45 KT  50 MPH
 12H  23/0600Z 10.0N  46.8W   55 KT  65 MPH
 24H  23/1800Z 10.1N  49.2W   65 KT  75 MPH
 36H  24/0600Z 10.3N  51.8W   70 KT  80 MPH
 48H  24/1800Z 10.8N  54.6W   70 KT  80 MPH
 60H  25/0600Z 11.3N  57.6W   65 KT  75 MPH
 72H  25/1800Z 12.1N  60.8W   60 KT  70 MPH
 96H  26/1800Z 14.0N  67.5W   50 KT  60 MPH
120H  27/1800Z 15.0N  72.5W   40 KT  45 MPH

$$
Forecaster Beven
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