Tropical Storm SIMON

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TROPICAL STORM SIMON DISCUSSION NUMBER   9
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP192014
200 PM PDT FRI OCT 03 2014

Recent visible imagery shows that Simon is getting better
organized, with the inner core convection now wrapping around the
center.  In addition, a recent TRMM overpass shows a well-defined
low-level circulation center, and a recent ASCAT overpass shows a
few vectors of 50-55 kt.  Satellite intensity estimates from TAFB
and SAB are 55 kt, and that will be the initial intensity.

The initial motion is 285/8.  Simon should move generally west-
northwestward for the next 24-36 hours as it is steered by
the subtropical ridge to the north and northeast.  After that time,
the track guidance remains very divergent.  The GFS, GFS ensemble
mean, and GFDL forecast Simon to recurve through a break in the
ridge near 116W-117W and move inland over the Baja California
peninsula and northwestern Mexico.  The GFS has shifted somewhat
westward since the last advisory, but this did not change its
forecast scenario.  The ECMWF, NAVGEM, and Canadian models show
Simon moving farther west, with a northward turn delayed until the
cyclone is near 120W. The ECMWF and Canadian subsequently show Simon
dissipating over water. Overall, the guidance envelope has shifted a
little to the west at 48-120 hours since the last advisory, and the
official forecast does as well.  The new forecast lies between the
TVCE consensus and the Florida State Superensemble from 48-120
hours, but is notably slower than both of those models.

Simon will be moving over warmer water with SSTs near 28-29C while
the deep-layer vertical shear is expected to be light.  This should
allow continued strengthening until the cyclone encounters cooler
waters in about 36 hours.  The new intensity forecast has been
increased over the previous forecast from 12-96 hours based on
current trends and the latest SHIPS model guidance.  There remain
two major sources of uncertainty in the intensity forecast.  The
first is that rapid intensification could occur during the next 24
hours or so.  Second, how much cool water Simon will encounter is
dependent on the track. The GFS/GFS Ensemble Mean/GFDL track would
keep the storm over relatively warm water, while the ECMWF/NAVGEM/
Canadian track would take it over much cooler water.

The ASCAT data shows that Simon remains a very small cyclone in
terms of size, with tropical-storm force winds extending no more
than 40 n mi from the center.


FORECAST POSITIONS AND MAX WINDS

INIT  03/2100Z 18.8N 110.6W   55 KT  65 MPH
 12H  04/0600Z 19.2N 112.2W   65 KT  75 MPH
 24H  04/1800Z 20.0N 114.3W   75 KT  85 MPH
 36H  05/0600Z 20.9N 115.6W   80 KT  90 MPH
 48H  05/1800Z 21.9N 116.4W   80 KT  90 MPH
 72H  06/1800Z 23.5N 116.5W   65 KT  75 MPH
 96H  07/1800Z 24.5N 116.0W   50 KT  60 MPH
120H  08/1800Z 25.5N 115.5W   35 KT  40 MPH

$$
Forecaster Beven

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