Hurricane RACHEL

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HURRICANE RACHEL DISCUSSION NUMBER  16
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP182014
200 AM PDT SUN SEP 28 2014

Rachel's eye disappeared for a few hours, but it is now becoming
distinct again.  Final-T numbers from TAFB and SAB decreased at 0600
UTC, but the initial intensity is held at 75 kt based on CI numbers
of 4.5/77 kt and an ADT estimate of T4.4/75 kt.  If Rachel is going
to strengthen further, it probably has another 6-12 hours to do so
before vertical shear begins to increase out of the south and
southwest.  In addition, Rachel will be moving into a drier
environment over the next couple of days, and upwelling of colder
ocean water could have a greater-than-normal influence on the
intensity since the cyclone will become nearly stationary in a day
or two.  The SHIPS and LGEM models show Rachel increasing in
strength just a bit later today and then only gradually weaken the
system through 48 hours.  In contrast, the GFDL, HWRF, and FSU
Superensemble show weakening beginning soon and predict a faster
weakening rate during the next two days.  Given the hurricane's
improving appearance in satellite imagery, the official forecast
still allows some strengthening in the short term.  After 24 hours,
the NHC forecast shows steady weakening and essentially splits the
difference between the two model scenarios.

Rachel is moving slowly north-northwestward--335 degrees at 5 kt--
through a break in the subtropical ridge caused by a deep-layer low
over the western United States.  The steering currents near Rachel
are forecast to collapse during the next few days after the
deep-layer low moves eastward, and the cyclone is expected to
become nearly stationary in 36-48 hours.  Once the vertical shear
increases, the low-level circulation is expected to begin moving
southwestward and west-southwestward in the trade wind flow.  The
track guidance, in particular the ECMWF, is not as far south on
this cycle, and the new NHC track forecast is therefore shifted
north and west during the remnant low phase.

FORECAST POSITIONS AND MAX WINDS

INIT  28/0900Z 21.1N 117.0W   75 KT  85 MPH
 12H  28/1800Z 21.6N 117.2W   80 KT  90 MPH
 24H  29/0600Z 22.2N 117.4W   70 KT  80 MPH
 36H  29/1800Z 22.4N 117.5W   60 KT  70 MPH
 48H  30/0600Z 22.2N 117.6W   45 KT  50 MPH
 72H  01/0600Z 21.6N 118.2W   30 KT  35 MPH...POST-TROP/REMNT LOW
 96H  02/0600Z 21.3N 119.2W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  03/0600Z 21.0N 121.0W   20 KT  25 MPH...POST-TROP/REMNT LOW

$$
Forecaster Berg

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