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Tropical Storm GONZALO


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TROPICAL STORM GONZALO DISCUSSION NUMBER   3
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL082014
1100 PM AST SUN OCT 12 2014

The circulation of Gonzalo, which has shown some signs of inner-core
features, is apparent in radar imagery from Guadeloupe, but the
cyclone's overall convective pattern is somewhat disorganized in
satellite imagery. A small area of central convection is noted near
the center, along with a rather linear convective band in the
eastern semicircle. Little deep convection is noted west of the
center, perhaps due to westerly shear of around 10 kt and some dry
air in the mid and upper levels seen in radiosonde data from St.
Maarten. The initial intensity remains 40 kt based on the earlier
aircraft data and a blend of the latest Dvorak data-T numbers from
TAFB and SAB. The SHIPS model shows the shear weakening in 12 to 18
hours, and most of the intensity guidance shows Gonzalo reaching
hurricane status in about 36 hours. Additional intensification is
forecast after that time in a low-shear environment over warm
waters. The new NHC intensity forecast is largely an update of the
previous one and is close to the IVCN consensus through the period.

The initial motion estimate is 275/10, as Gonzalo is being steered
by a mid-level ridge to its northeast. During the next 36 to 48
hours, the cyclone will gradually turn northwestward as it moves
around the western periphery of this ridge. Overall, the guidance
envelope has shifted a little to the right through the first 2 days,
and the NHC forecast has been adjusted in that direction but lies
south of the multi-model consensus and close to the ECMWF. After
that time, most of the guidance shows the cyclone turning northward
into a weakness in the ridge and then accelerating northeastward
ahead of a mid-latitude trough by day 5. There is still a large
amount of along-track spread at these time ranges, with the GFS,
HWRF, GFDL, and GEFS ensemble mean showing a faster northeastward
acceleration, and the slower ECMWF showing the trough missing
Gonzalo and leaving the cyclone moving slowly northeastward
by the end of the period. At days 3 through 5, the NHC forecast is
faster and shows more of a northeastward motion compared to the
previous one, but is much slower than the GFS and south of the
consensus out of respect for the ECMWF model.

FORECAST POSITIONS AND MAX WINDS

INIT  13/0300Z 16.6N  60.2W   40 KT  45 MPH
 12H  13/1200Z 16.9N  61.9W   50 KT  60 MPH
 24H  14/0000Z 17.7N  63.8W   55 KT  65 MPH
 36H  14/1200Z 18.8N  65.3W   65 KT  75 MPH
 48H  15/0000Z 20.0N  66.5W   70 KT  80 MPH
 72H  16/0000Z 22.5N  68.0W   85 KT 100 MPH
 96H  17/0000Z 24.5N  68.0W   95 KT 110 MPH
120H  18/0000Z 27.0N  66.0W   90 KT 105 MPH

$$
Forecaster Brennan

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