[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT42 KNHC 241458
TCDAT2

Tropical Storm Gonzalo Discussion Number  12
NWS National Hurricane Center Miami FL       AL072020
1100 AM AST Fri Jul 24 2020

Gonzalo continues to produce bursts of deep convection, especially
in the southeast quadrant, but has not become any better organized
overall since the last advisory. Microwave imagery overnight
indicated the low-level structure of Gonzalo is still largely
intact, but this has not translated into better convective
organization. ASCAT data valid shortly after 12Z revealed that
Gonzalo has accelerated west faster than anticipated and has not
strengthened. In fact the strongest winds in the ASCAT data were
only 30-35 kt. The resolution of ASCAT likely limits its ability to
sample the actual max winds of small storms like Gonzalo, but it is
another indication that the cyclone has not strengthened and could
be weakening. The initial intensity for this advisory is set
at 45 kt, based primarily on the latest TAFB Dvorak fix and the
UW-CIMSS SATCON. An Air Force Reserve reconnaissance aircraft
scheduled to investigate the storm this afternoon will provide a
more information about Gonzalo's intensity and structure.

Due primarily to the adjusted initial position, the NHC track
forecast has been adjusted a fair amount west and south of the
previous advisory. Overall Gonzalo is still forecast to move
generally westward or west-northwestward through the period,
steered by the subtropical ridge to the north. The new NHC forecast
lies between the old forecast, adjusted for the new initial
position, and the HFIP Corrected Consensus.

The intensity guidance is generally lower than it has been for the
last day or so, and none of the operational models forecast Gonzalo
to reach hurricane strength. Unfortunately, small storms like
Gonzalo are often subject to large swings in intensity, up or down,
and that aspect of the forecast remains highly uncertain, even
though the spread in the guidance is not particularly high. The NHC
forecast has been adjusted only slightly lower for this cycle and
is now above all of the guidance at the time the system is
forecast to pass through the Windward Islands. A larger
adjustment could be made later today if the most recent model
trends continue, or if the recon mission finds that Gonzalo is even
weaker than the current estimates.


Key Messages

1. Gonzalo is forecast to bring tropical storm conditions across
portions of the southern Windward Islands Saturday and Saturday
night. Hurricane and Tropical Storm Warning and Watches are
currently in effect for some of the islands. Interests in the
southern Windward Islands should monitor the progress of Gonzalo and
follow any advice given by local officials.

2. Gonzalo is expected to produce heavy rain over portions of the
southern Windward Islands. This could lead to life-threatening
flash flooding.

FORECAST POSITIONS AND MAX WINDS

INIT  24/1500Z 10.0N  54.2W   45 KT  50 MPH
 12H  25/0000Z 10.5N  56.0W   50 KT  60 MPH
 24H  25/1200Z 11.4N  59.1W   55 KT  65 MPH
 36H  26/0000Z 12.4N  62.3W   60 KT  70 MPH
 48H  26/1200Z 13.0N  65.7W   50 KT  60 MPH
 60H  27/0000Z 13.7N  69.0W   40 KT  45 MPH
 72H  27/1200Z 14.0N  72.0W   30 KT  35 MPH
 96H  28/1200Z...DISSIPATED

$$
Forecaster Zelinsky
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