Tropical Storm RACHEL

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TROPICAL STORM RACHEL DISCUSSION NUMBER   8
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP182014
200 AM PDT FRI SEP 26 2014

Microwave data indicate that Rachel's structure has changed
little during the past few hours, and the maximum winds are
therefore held at 45 kt.  Deep convection remains limited to the
southwest of the low-level center, although a recent expansion of
the cold cloud tops in infrared satellite imagery suggests that the
northeasterly shear may be relaxing just a bit.  The SHIPS guidance
indicates that the shear should gradually diminish, reaching a
minimum in about 36 hours, so gradual strengthening is anticipated
up through that time.  After 36 hours, the shear is expected to
increase while Rachel moves over marginally cooler water and into a
drier, more stable environment.  Steady weakening is expected to
begin by 48 hours, with the cyclone likely becoming a remnant low
by day 5.  The updated NHC intensity forecast is not too dissimilar
from the previous one.  However, it should be noted that the
60-kt forecast peak intensity is a little higher than all of the
guidance except the HWRF.

Rachel's initial motion is 300/12 kt.  The track models are in good
agreement during the first 36-48 hours, showing Rachel slowing down
and turning north-northwestward toward a break in the subtropical
ridge.  There is significant divergence in the guidance after 48
hours, however.  The notable outliers are the GFS and the GFDL
ensemble mean, which have a stronger cyclone being pulled
northeastward toward the Baja California peninsula by a deep-layer
trough over the southwestern United States.  The other models show
a weaker cyclone stalling and then turning southward or
southwestward within the prevailing low-level flow.  Due to the
model divergence, very slow motion is indicated between days 3-5,
and Rachel is expected to become nearly stationary before drifting
southwestward during its remnant low stage.  The guidance shifted a
bit to the west on this cycle, and although the NHC forecast was
also nudged in that direction, it still lies on the eastern edge of
the envelope.

FORECAST POSITIONS AND MAX WINDS

INIT  26/0900Z 18.0N 112.9W   45 KT  50 MPH
 12H  26/1800Z 18.7N 114.3W   50 KT  60 MPH
 24H  27/0600Z 19.7N 115.4W   55 KT  65 MPH
 36H  27/1800Z 20.6N 116.2W   60 KT  70 MPH
 48H  28/0600Z 21.4N 116.7W   55 KT  65 MPH
 72H  29/0600Z 22.7N 116.8W   45 KT  50 MPH
 96H  30/0600Z 23.0N 116.5W   35 KT  40 MPH
120H  01/0600Z 22.5N 117.0W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Berg

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