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Hurricane Sergio Discussion Number  25
NWS National Hurricane Center Miami FL       EP212018
800 AM PDT Fri Oct 05 2018

GOES-16 images and a 1054 UTC ATMS microwave overpass indicate
that Sergio's 25 n mi eye has become a bit ragged this morning, and
has continued to cool.  Despite the eye's irregularity, the inner
core convection is still intact and is producing very cold (-76C)
cloud tops.  Primarily due to the eye adjustment temperature,
however, the subjective and objective satellite intensity estimates,
as well as a recent SATCON analysis, have again decreased to 95-100
kt, and the initial intensity is subsequently lowered to 100 kt.

Although due to the possibility of unpredicted inner core structure
changes in the short term which could cause Sergio to strengthen
again, the current weakening trend is expected to continue through
day 5 as Sergio moves toward decreasing oceanic temperatures and
into a stabilizing surrounding atmosphere.  The statistical
intensity guidance as well as the large-scale models show increasing
southwesterly shear entering the picture after 72 hours.  This
should also aid in the forecast weakening trend.  The official
forecast is just an update of the previous one and follows the
NOAA-HCCA consensus and is just above the Florida State
Superensemble.

Sergio is moving a little left of the previous 6-hr motion...now
westward, or 280/7 kt.  A gradual turn toward the west-southwest
during the next 36 hours is expected as high pressure located
north-northeast of the Hawaiian Islands builds to the north of
Sergio.  Over the weekend, a decrease in forward speed and a turn
toward the northwest is forecast as the aforementioned mid-level
high retrogrades in response to an amplifying trough over the
southwestern United States and Baja California peninsula. Beyond the
72 hour period, increasing southwesterly mid-tropospheric flow
should induce a northeastward accelerated motion through the
remaining portion of the forecast.  The NHC forecast is adjusted a
little toward the south of the last advisory through 72 hours to
agree more with the various consensus models, but is quite similar
in motion and forward speed beyond that period.


FORECAST POSITIONS AND MAX WINDS

INIT  05/1500Z 15.9N 121.8W  100 KT 115 MPH
 12H  06/0000Z 15.8N 122.7W   95 KT 110 MPH
 24H  06/1200Z 15.5N 123.8W   90 KT 105 MPH
 36H  07/0000Z 15.2N 125.0W   85 KT 100 MPH
 48H  07/1200Z 15.3N 126.0W   85 KT 100 MPH
 72H  08/1200Z 16.5N 126.8W   80 KT  90 MPH
 96H  09/1200Z 18.5N 125.0W   70 KT  80 MPH
120H  10/1200Z 21.5N 120.8W   60 KT  70 MPH

$$
Forecaster Roberts

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