Tropical Storm SIMON

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TROPICAL STORM SIMON DISCUSSION NUMBER   7
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP192014
200 AM PDT FRI OCT 03 2014


Microwave satellite images early this morning indicate that the
inner-core region of Simon is not particularly well organized. A
low-level eye feature has been intermittent since about 0000 UTC,
but the most recent images do not show the eye feature any longer.
Subjective and objective satellite intensity estimates suggest that
Simon has strengthened to 55-60 kt based on a CDO feature. However,
two ASCAT overpasses at 0412 UTC and 0504 UTC only indicated surface
winds of 39 kt and 41 kt, respectively. Even allowing for some
undersampling due to the compact size of the cyclone likely only
yields 45-50 kt. Owing to the lack of persistent central features,
the initial intensity is being held at 45 kt for this advisory.

The initial motion is an uncertain 280/06 kt and is based primarily
on microwave satellite fixes. There remains high confidence that
Simon will continue to move westward to west-northwestward for the
next 2-3 days as the cyclone navigates around the western periphery
of a strong deep-layer ridge located north of the cyclone. After
that time, however, the model guidance diverges quite significantly.
The overwhelming majority of the guidance recurves Simon toward the
north by Day 4 and toward the northeast by Day 5. However, the very
reliable ECMWF model takes Simon farther west through Day 5 and
does not recurve the cyclone until after this forecast period.
Owing to the significant differences in the various model solutions,
and out of respect for the ECMWF model, and given that mid-level
northwesterly flow patterns are not conducive for recurvature
scenarios, the official forecast was only nudged a little to the
west of the previous forecast track.

Simon will be moving over warmer water with SSTs near 28-29C during
the next 24-36 hours while the deep-layer vertical shear is light.
However, modest easterly mid-level shear that has been undercutting
the otherwise impressive outflow pattern may continue to
occasionally disrupt the inner core convection before Simon reaches
cooler water and a drier, more stable airmass by Days 4 and 5. As
a result, only slow steady strengthening is forecast, which is
similar to the SHIPS intensity model and the previous forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  03/0900Z 18.3N 108.9W   45 KT  50 MPH
 12H  03/1800Z 18.7N 110.3W   55 KT  65 MPH
 24H  04/0600Z 19.3N 112.2W   65 KT  75 MPH
 36H  04/1800Z 20.0N 114.1W   75 KT  85 MPH
 48H  05/0600Z 21.0N 115.8W   75 KT  85 MPH
 72H  06/0600Z 22.5N 116.5W   60 KT  70 MPH
 96H  07/0600Z 24.0N 116.0W   50 KT  60 MPH
120H  08/0600Z 25.0N 115.5W   35 KT  40 MPH

$$
Forecaster Stewart

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