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Hurricane ALETTA


Hurricane Aletta Discussion Number  14
NWS National Hurricane Center Miami FL       EP022018
900 PM MDT Fri Jun 08 2018

Aletta's weakening phase has begun, with the eye becoming cloud
filled in visible satellite imagery since the last advisory.
An analysis from CIMSS at the University of Wisconsin indicates that
vertical shear has increased to 15-20 kt out of the south-southwest,
and a 2309 UTC SSMI/S pass confirms that the hurricane's structure
is responding to that shear.  All final-T numbers have decreased,
and the initial intensity is set at 110 kt as a blend of the various
final-T and CI numbers.  This is also supported by the latest SATCON

Vertical shear is forecast to strengthen during the next 36 hours,
and Aletta will be moving over marginally warm sea surface
temperatures, both of which should cause the cyclone to continue
weakening.  The new intensity models are now showing a much more
significant rate of weakening, and the updated NHC intensity
forecast follows suit, bringing down the winds much faster than
shown in the previous forecast.  The NHC forecast is near the top
end of the guidance for the first 24 hours and then close to the
ICON intensity consensus from 36 hours and beyond.  Interestingly,
the HCCA guidance weakens Aletta to a tropical storm within 24
hours, so it wouldn't be surprising if the hurricane weakens faster
than shown in the official forecast.  Aletta is now forecast to
degenerate into a remnant low by day 3.

The initial motion estimate is 285/5 kt.  Since Aletta is moving
around the southwestern periphery of a mid-level ridge centered over
northwestern Mexico, the cyclone is expected to maintain a slow
west-northwestward or northwestward motion for the next 36 hours.
After that time, the weakening storm should turn back toward the
west and eventually southwest as it becomes increasingly steered by
the low-level trade winds and the flow around another developing
tropical cyclone to the east.  The new NHC track forecast is a
little south of the previous forecast to account for an overall
southward shift in the guidance envelope.


INIT  09/0300Z 16.2N 112.3W  110 KT 125 MPH
 12H  09/1200Z 16.6N 113.1W   95 KT 110 MPH
 24H  10/0000Z 17.3N 114.2W   75 KT  85 MPH
 36H  10/1200Z 17.7N 115.2W   55 KT  65 MPH
 48H  11/0000Z 17.8N 116.3W   40 KT  45 MPH
 72H  12/0000Z 17.8N 118.7W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  13/0000Z 17.5N 121.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  14/0000Z 16.5N 122.5W   20 KT  25 MPH...POST-TROP/REMNT LOW

Forecaster Berg