Tropical Storm SIMON

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TROPICAL STORM SIMON DISCUSSION NUMBER  19
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP192014
200 AM PDT MON OCT 06 2014

Simon's cloud pattern continues to deteroriate.  Microwave data
indicate that the cyclone's low-level center is exposed to the
southwest of the main convective mass due to strong southwesterly
vertical wind shear.  The remaining central convection is no longer
very deep either, with cloud top temperatures having risen to -50
to -60 deg C.  A large plume of stratiform rain and high clouds
also extends well north and east of the center, though even this
area has been shrinking.  The initial wind speed is reduced to 50 kt
based on a blend of Final T-numbers of 3.0/45 kt and 3.5/55 kt from
TAFB and SAB, respectively, which should provide a reasonable
estimate of the intensity in cases of rapid weakening.

Extremely strong west-southwesterly vertical shear of 30-40 kt
will cause a decoupling of the cyclone during the next day or two,
while very unfavorable thermodynamic conditions should result in a
loss of deep convection.  This should cause the rapid weakening
trend observed during the past 24 hours to continue, and remnant low
status is now predicted in 36 hours or perhaps sooner.  The remnant
circulation could dissipate prior to reaching the Baja California
peninsula, as indicated by the latest SHIPS model output, or in the
very least arrive in a greatly weakened state.  The NHC wind speed
forecast is largely an update of the previous one in agreement with
the latest multi-model consensus.

Simon has turned northward, or 360/06, around the western periphery
of a subtropical ridge extending westward near the southwestern
coast of Mexico.  A shortwave trough moving toward southern
California should turn the cyclone north-northeastward in the next
12 to 24 hours, but Simon will have just begun to recurve when it
shears apart.  The track guidance shows the remnant circulation
continuing north-northeastward at varying forward speeds, with the
GFS still much faster than the ECMWF and UKMET.  The NHC track
forecast is very near the previous one and the multi-model consensus
through 48 hours but is slower after that time to acknowledge the
possibility that a weaker system than depicted in global model
fields might not reach the northern Baja California peninsula.

Even if Simon or its remnant circulation does not make it across the
rugged terrain of the Baja California peninsula, moisture associated
with this system is expected to spread across the northern Baja
California peninsula, northwestern Mexico, and into the U.S. Desert
Southwest, which could trigger heavy rains in those regions during
the next few days.

FORECAST POSITIONS AND MAX WINDS

INIT  06/0900Z 24.4N 117.6W   50 KT  60 MPH
 12H  06/1800Z 25.3N 117.5W   40 KT  45 MPH
 24H  07/0600Z 26.4N 117.0W   30 KT  35 MPH
 36H  07/1800Z 27.6N 116.3W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  08/0600Z 28.8N 115.4W   20 KT  25 MPH...POST-TROP/REMNT LOW
 72H  09/0600Z 30.2N 114.2W   15 KT  15 MPH...POST-TROP/REMNT LOW
 96H  10/0600Z...DISSIPATED

$$
Forecaster Kimberlain

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