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Hurricane Aletta Discussion Number  12
NWS National Hurricane Center Miami FL       EP022018
900 AM MDT Fri Jun 08 2018

The remarkable intensification of Aletta has continued through this
morning.  The eye has become clear and at times has been
surrounded by a closed ring of cloud tops colder than -70 deg C.
The initial intensity of 120 kt is based on a blend of subjective
and objective Dvorak estimates.  It is noteworthy that the
intensity of Aletta has increased by an estimated 60 kt in just 24
hours since yesterday morning.

The short-range intensity forecast is particularly difficult since
there are no obvious reasons why Aletta should cease
intensification.  Although the deep-layer wind shear is currently
very low and SSTs are warm enough to support further
intensification, nearly all of the intensity guidance indicates that
Aletta should have reached its peak.  Recent microwave imagery does
indicates that a secondary eyewall has not yet formed, however
the resolution of the instruments could limit our ability to detect
such a feature.  Given the low bias of the guidance for Aletta so
far, the new forecast allows for some slight additional
strengthening during the day today.  By 24 hours, moderate shear
should cause the hurricane to begin weakening steadily, with rapid
weakening occuring between 36 and 72 h while Aletta traverses a
strong SST gradient.  Due to the higher initial intensity of Aletta,
the official forecast is a little higher than the previous one for
the first 24 hours, but very similar thereafter.

Almost no change has been to the track forecast.  A broad
upper-level trough over the eastern Pacific should cause Aletta to
turn more toward the northwest in 24 to 36 h.  After Aletta rapidly
weakens over the weekend, the lower-level trade winds will become
the dominant steering flow, forcing the cyclone to turn back toward
the west.  Excluding the ECMWF which does not have a realistic
depiction of the major hurricane, the guidance has come into
somewhat better agreement today and confidence in the track
forecast has increased since yesterday.

FORECAST POSITIONS AND MAX WINDS

INIT  08/1500Z 15.8N 111.2W  120 KT 140 MPH
 12H  09/0000Z 16.3N 111.9W  125 KT 145 MPH
 24H  09/1200Z 17.0N 112.9W  110 KT 125 MPH
 36H  10/0000Z 17.9N 113.8W   85 KT 100 MPH
 48H  10/1200Z 18.6N 114.8W   65 KT  75 MPH
 72H  11/1200Z 19.5N 116.7W   35 KT  40 MPH
 96H  12/1200Z 20.0N 118.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  13/1200Z 20.0N 119.5W   20 KT  25 MPH...POST-TROP/REMNT LOW

$$
Forecaster Zelinsky

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