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Tropical Storm RICK


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TROPICAL STORM RICK DISCUSSION NUMBER   7
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP212015
800 PM MST THU NOV 19 2015

Rick's cloud pattern has eroded some during the past 6 hours with
previously solid bands of convection in the northern semicircle
having become more fragmented during the past few hours.
In addition, numerous small arc cloud lines have been noted
propagating away from the cyclone, which is indicative of dry
mid-level air having penetrated into the inner core region. This
supposition is further supported by a 20/0006 UTC AMSU pass
indicating only a narrow fragmented band of convection is present
in the northwestern quadrant of the storm. Therefore, the initial
intensity of 35 kt remains unchanged for this advisory, which is
lower than the available satellite intensity estimates.

The initial motion estimate is 295/09 kt and is based primarily on
passive microwave satellite data. A mid-level ridge over central
Mexico is forecast to build westward to the north and east of Rick
during the next 24-36 hours, while a large upper-level low located
near 27N 138W is expected to fill and gradually open up into a broad
trough by 48-72 hours. The combination of these two steering
mechanisms should keep Rick moving west-northwestward for the next
48 hours, followed by a decrease in forward speed and a gradual turn
toward the northwest and north at 72 h and 96 h, respectively. The
official forecast track was only nudged slightly to the left of the
previous advisory track, and essentially lies down the middle of NHC
track guidance envelope.

Rick is forecast to move into a weak vertical wind shear regime
during the next 24-36 hours while remaining over SSTs of 29 deg C.
These favorable conditions would normally support intensification of
a tropical cyclone. However, the ragged and elongated inner-core
wind field, coupled with additional entrainment of drier mid-level
air, is expected to inhibit any significant development and
organization of deep convection. By 48 hours and beyond, an increase
in southwesterly vertical wind shear to more than 25 kt is forecast
to induce gradual weakening, with Rick becoming a remnant low by 96
hours when the cyclone will be moving over cooler waters at that
time. Rick is expected to dissipate day 5, if not sooner. NHC
intensity forecast is a little lower than the previous advisory and
remains below the multi-model consensus, IVCN.

FORECAST POSITIONS AND MAX WINDS

INIT  20/0300Z 15.2N 108.1W   35 KT  40 MPH
 12H  20/1200Z 15.9N 109.5W   40 KT  45 MPH
 24H  21/0000Z 16.5N 111.1W   40 KT  45 MPH
 36H  21/1200Z 17.2N 112.4W   40 KT  45 MPH
 48H  22/0000Z 17.8N 113.4W   35 KT  40 MPH
 72H  23/0000Z 19.5N 115.0W   25 KT  30 MPH
 96H  24/0000Z 21.6N 115.6W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  25/0000Z...DISSIPATED

$$
Forecaster Stewart

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