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TROPICAL STORM PATRICIA DISCUSSION NUMBER   7
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP202015
1000 PM CDT WED OCT 21 2015

The convective cloud pattern of Patricia has improved significantly
since the previous advisory. A large CDO feature and a pronounced
curved convective band in the western semicircle has developed, and
a primitive eye feature has been noted in recent passive microwave
imagery.  The last report from a NOAA Hurricane Hunter aircraft
indicated a SFMR surface wind value of 56 kt, which arrived
after the previous advisory had been issued. That data, along with a
2056Z UW-CIMSS AMSU intensity estimate of 59 kt and the improved
satellite appearance, is the justification for increasing the
intensity to a conservative 55 kt.

The initial motion estimate is 290/12 kt. The new forecast track is
similar to the previous advisory track except to widen the turn
toward the northwest slightly in 24-36 hours. The new 18Z GFS model
shifted slightly westward and is now very close to the ECMWF
solution. As a result, the official forecast track has been nudged
slightly westward at the 24-, 36-, and 48-hours, which delays
landfall by another 6 hours or so. Otherwise, the track forecast
reasoning remains unchanged. Patricia is expected to move
west-northwestward along the south side of a deep-layer ridge over
the Gulf of Mexico for the next 24 hours, followed by a
gradual turn toward the northwest, and a turn toward the north at
36-48 hours. The model guidance remains in excellent agreement on
this track scenario, and the official forecast lies between the
GFS-ECMWF (GFEX) and TVCE consensus model tracks.

The improved organization of Patricia along with favorable
environmental and oceanic conditions consisting of low vertical
wind shear of less than 5 kt, a very moist mid-level environment,
SSTs in excess of 30 deg C, and high upper-ocean heat content values
in excess of 60 units support rapid intensification of the tropical
cyclone. The NHC intensity forecast closely follows the IVCN
consensus model through 24 hours and then is above the consensus
after that, following a blend of the SHIPS and LGEM models. The
justification for going above the IVCN consensus is due to the low
bias caused by the HWRF model, which moves Patricia inland sooner,
resulting in a much lower intensity at 48 hours. As a result, rapid
intensification is explicitly forecast for the next 36 hours, making
Patricia a major hurricane by the end of that period. The intensity
is then leveled off at 48 hours due to the possibility of modest
southerly wind shear and some land interaction affecting the cyclone
as Patricia nears the coast of southwestern Mexico.

FORECAST POSITIONS AND MAX WINDS

INIT  22/0300Z 13.5N 100.5W   55 KT  65 MPH
 12H  22/1200Z 14.2N 102.1W   70 KT  80 MPH
 24H  23/0000Z 15.5N 103.8W   85 KT 100 MPH
 36H  23/1200Z 17.0N 104.9W  100 KT 115 MPH
 48H  24/0000Z 19.0N 105.0W  100 KT 115 MPH
 72H  25/0000Z 24.1N 103.2W   30 KT  35 MPH...INLAND
 96H  26/0000Z...DISSIPATED

$$
Forecaster Stewart

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