Tropical Storm RACHEL

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TROPICAL STORM RACHEL DISCUSSION NUMBER   9
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP182014
800 AM PDT FRI SEP 26 2014

The organization of Rachel's cloud pattern has not changed this
morning. The center of the cyclone remains on the northeast
(upshear) side and outside of a large mass of very cold-topped
convection, presumably a result of some northeasterly vertical wind
shear. The deep convection continues to regularly burst, a trend
that has been observed for a few days now. The initial intensity
estimate is held at 45 kt in agreement with the 1200 UTC Dvorak fix
from TAFB.  Global models show Rachel moving underneath an upper-
level ridge axis during the next 24 hours or so, which should result
in a relaxation of the persistent shear and allow for some
intensification since the storm will still be over warm enough
waters.  In 2-3 days, Rachel will have moved far enough to the north
to experience an increase of southwesterly shear in response to a
mid-latitude trough over the western United States.  That shear and
increasingly unfavorable thermodynamics factors, including somewhat
cooler waters, are expected to hasten its weakening beyond 48 hours.
The NHC intensity forecast is not much different than the previous
one, and still shows remnant low status at the end of the forecast
period.

Rachel continues on a west-northwesterly track of 295/12.  The
cyclone is forecast to turn toward the northwest and north-
northwest with a significant decrease in forward speed during the
next couple of days when it encounters a weakness caused by the
earlier-mentioned western United States trough. By 48 hours, there
is a rather distinct split in the track guidance, with the GFS-based
model solutions carrying the cyclone quickly northward and
northeastward while the ECMWF/UKMET suggest a weaker cyclone
steered toward the west-northwest and west. The NHC track forecast
stays left of but closer to the GFS through 48 hours due to Rachel's
forecast intensification and then shows slow motion for the
remainder of the forecast period.  The 48-120 hour portion of the
track forecast is very near the multi-model consensus, TVCE, and it
could trend westward in future forecasts if confidence in a weaker
cyclone at that time frame increases.



FORECAST POSITIONS AND MAX WINDS

INIT  26/1500Z 18.2N 114.4W   45 KT  50 MPH
 12H  27/0000Z 19.0N 115.2W   50 KT  60 MPH
 24H  27/1200Z 20.0N 116.1W   55 KT  65 MPH
 36H  28/0000Z 20.9N 116.8W   60 KT  70 MPH
 48H  28/1200Z 21.8N 117.1W   50 KT  60 MPH
 72H  29/1200Z 22.8N 117.2W   40 KT  45 MPH
 96H  30/1200Z 23.0N 117.2W   30 KT  35 MPH
120H  01/1200Z 22.8N 117.4W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Kimberlain

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