Tropical Storm RACHEL

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TROPICAL STORM RACHEL DISCUSSION NUMBER  12
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP182014
200 AM PDT SAT SEP 27 2014

Rachel's convective structure has evolved since the last advisory.
The long curved band noted earlier has become broken and is
separated from a small, compact area of deep convection which has
developed over the low-level center.  An eye-like feature has
also occasionally appeared in infrared satellite imagery.  Maximum
winds are held at 55 kt based on a consensus of T3.5/55 kt Dvorak
estimates from TAFB and SAB.  Rachel is forecast to be in a
low-shear environment for the next 36 hours or so, and the
atmosphere should be sufficiently moist and unstable to support some
strengthening in the short term.  After 48 hours, southwesterly
vertical shear of 15-20 kt is forecast to develop, and Rachel will
be moving into a much drier and stable environment.  The intensity
models are in good agreement that Rachel should be at or just below
hurricane intensity in 24 hours, which is indicated in the official
forecast.  Thereafter, the dynamical models show a faster rate of
weakening than the statistical models, and the NHC forecast closely
follows the multi-model consensus ICON.

Rachel has turned northwestward, or 315/7 kt, into a weakness in
the subtropical ridge caused by two deep-layer lows over California
and the Rio Grande Valley.  As the low over California moves
eastward, steering currents are expected to collapse, and Rachel
should turn north-northwestward but slow down and become nearly
stationary in 2-3 days.  Once vertical shear increases on day 3,
a less-vertically-deep Rachel is expected to begin drifting
southwestward in the prevailing low-level flow.  The GFS, GFDL, and
GFDL ensemble mean have begun to pull back a bit on their previous
trend of showing Rachel turning northeastward toward the Baja
California peninsula, although there is still considerable spread
in the track guidance by days 4 and 5.  The updated NHC track
forecast essentially maintains continuity with the previous forecast
and is not too far from the multi-model consensus TVCE.

FORECAST POSITIONS AND MAX WINDS

INIT  27/0900Z 19.1N 115.8W   55 KT  65 MPH
 12H  27/1800Z 19.8N 116.3W   60 KT  70 MPH
 24H  28/0600Z 20.7N 116.6W   65 KT  75 MPH
 36H  28/1800Z 21.5N 116.8W   60 KT  70 MPH
 48H  29/0600Z 21.9N 116.9W   50 KT  60 MPH
 72H  30/0600Z 22.1N 117.0W   35 KT  40 MPH
 96H  01/0600Z 21.5N 117.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  02/0600Z 21.0N 118.0W   20 KT  25 MPH...POST-TROP/REMNT LOW

$$
Forecaster Berg

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