Hurricane SIMON

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HURRICANE SIMON DISCUSSION NUMBER  11
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP192014
200 AM PDT SAT OCT 04 2014

Microwave satellite imagery between 0000 UTC and 0500 UTC indicate
that the inner-core convection had been unable to consolidate around
the center and maintain a closed eye feature. A 0442 UTC AMSU
overpass revealed that the eye of Simon was open in the northwest
quadrant. Since that time, however, infrared satellite imagery
indicates that a warm spot has developed near the center of a more
symmetrical and growing CDO feature, suggesting that Simon might
finally be getting more vertically coherent. The initial intensity
has been increased to 75 kt based on a Dvorak intensity estimate of
T4.5/77 kt from TAFB and the recent appearance of a warm spot in the
CDO cloud canopy.

The initial motion is 290/10 kt, which is based on several microwave
satellite positions. There is basically no significant change to the
previous track forecast or reasoning. The 00 UTC model guidance
shows less divergence than previous runs, especially through 36
hours. After that time, the models show some noticeable difference
on when and where Simon is expected to gradually recurve to the
northeast when the cyclone nears the subtropical ridge axis that is
situated along 23N-24N latitude. The GFS, GFS-ensemble mean, and
HWRF models show a sharper and earlier turn to the northeast by
about 48 hours due to a weaker ridge, whereas the ECMWF, UKMET,
GFDL and NAVGEM models have Simon moving farther west and making a
wider and slower turn. Given the high amplitude nature of the large
mid-latitude ridge over the western U.S. and eastern Pacific and the
deepening trough over the eastern United States, which should help
to sustain the current steering flow pattern, the official forecast
leans more toward the farther west and slower recurvature model
solutions. The NHC forecast track is similar to but a little to the
west of the previous forecast track and the consensus model TVCN.

The global models indicate that the current impressive outflow and
low vertical wind shear patterns surrounding Simon are expected to
persist for at least the next 36 hours or so. However, the most
significant strengthening, possibly even rapid intensification, is
most likely to occur during the next 24 hours while the hurricane
remains over sea-surface temperatures of 27-28C and where the depth
of the warm water is sufficient to prevent any significant cold
upwelling beneath Simon. By 36 hours, passage over cooler SSTs
should induce gradual weakening, followed by more rapid weakening on
Days 4 and 5 when southwesterly vertical wind shear is expected to
increase to 25-40 kt. Simon is forecast to become a remnant low by
120 hours, but this could occur sooner if the cyclone moves farther
west than the official forecast track is indicating, which would
bring the cyclone over colder water. A NOAA Hurricane Hunter
aircraft is scheduled to conduct a research flight into Simon around
1800 UTC today, at which time a better estimate of the strength of
the hurricane will be obtained.

FORECAST POSITIONS AND MAX WINDS

INIT  04/0900Z 19.5N 112.7W   75 KT  85 MPH
 12H  04/1800Z 20.2N 114.4W   85 KT 100 MPH
 24H  05/0600Z 21.4N 116.2W   95 KT 110 MPH
 36H  05/1800Z 22.3N 117.2W   80 KT  90 MPH
 48H  06/0600Z 23.3N 117.6W   70 KT  80 MPH
 72H  07/0600Z 24.4N 117.4W   55 KT  65 MPH
 96H  08/0600Z 25.2N 117.0W   35 KT  40 MPH
120H  09/0600Z 26.3N 116.1W   30 KT  35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Stewart

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