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Hurricane Fernanda Discussion Number  17
NWS National Hurricane Center Miami FL       EP062017
800 PM PDT Sat Jul 15 2017

Recent microwave imagery, including a just-received GPM overpass,
indicate that Fernanda continues to have concentric eyewalls with
diameters of roughly 10 and 45 n mi.  The eye has become less
distinct in conventional satellite imagery since the last advisory,
and the central convection has become more ragged.  Based on this,
the initial intensity is lowered to 110 kt, which is a little below
the average of the various satellite intensity estimates.  While the
inner core has become a little less organized since yesterday, the
hurricane has developed a large and symmetric area of outer
convective banding.

Fernanda has about 24 h more in a warm-water, light-shear
environment.  The intensity forecast is based on the premise that
the current eyewall replacement cycle will finish before the
hurricane leaves the warmest water, and thus it calls for some
re-intensification during that time.  From 24-96 h, Fernanda
should remain in a light shear environment, but will move over
decreasing sea surface temperatures and into a drier air mass.
After 96 h, the cyclone will also encounter significant westerly
shear.  The intensity forecast thus calls for steady to rapid
weakening after 36 h.  Overall, the new intensity forecast is a
little higher than the model consensus for the first 36 h and near
the consensus after that.

Fernanda is now moving 285/12, steered by a mid- to upper-level
ridge to the north and northeast.  A west-northwestward motion is
expected to continue for the next several days while the hurricane
moves toward a weakness at the western periphery of the ridge.
After 96 h, most of the guidance suggests that Fernanda should turn
westward as it weakens and becomes steered by the low-level
subtropical ridge.  The new forecast track remains near the middle
of the guidance envelope and in best agreement with the various
consensus models.


FORECAST POSITIONS AND MAX WINDS

INIT  16/0300Z 11.7N 125.4W  110 KT 125 MPH
 12H  16/1200Z 12.4N 127.3W  115 KT 130 MPH
 24H  17/0000Z 13.2N 129.5W  120 KT 140 MPH
 36H  17/1200Z 14.0N 131.6W  115 KT 130 MPH
 48H  18/0000Z 14.7N 133.3W  100 KT 115 MPH
 72H  19/0000Z 16.5N 136.0W   75 KT  85 MPH
 96H  20/0000Z 17.5N 139.0W   55 KT  65 MPH
120H  21/0000Z 17.5N 142.5W   40 KT  45 MPH

$$
Forecaster Beven

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