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Hurricane Fernanda Discussion Number   8
NWS National Hurricane Center Miami FL       EP062017
200 PM PDT Thu Jul 13 2017

Fernanda is rapidly intensifying.  Satellite imagery indicates that
the central convection has become more symmetric, and there have
been hints of an eye in visible imagery.  In addition, earlier
microwave imagery showed at lease a partial ring of convection
around the center.  Subjective and objective satellite intensity
estimates range from 65-75 kt, so the initial intensity is
increased to a possibly conservative 70 kt.  Conservative or not,
this is a 35 kt increase from this time yesterday.

The initial motion is a little south of west or 260/10, with part
of the southward component possibly due to some reformation of the
center as the cyclone intensified.  During the next 48 h, a
deep-layer ridge to the north of Fernanda should steer the
hurricane generally westward, and the new forecast is similar to
the previous forecast.  After that time, a large mid- to upper-level
trough over the central Pacific north of Hawaii should cause the
ridge to weaken, and the track guidance shows Fernanda turning
west-northwestward in response.  The guidance is forecasting a
greater northward component of motion from 72-120 h than on the
previous runs, and thus the latter part of the track forecast is
nudged northward as well.  Overall, the new forecast lies close to
the various consensus models.

While satellite imagery suggests that some shear continues to
affect Fernanda, so far it has done little to slow the development.
The hurricane should remain over warm water and in a light shear
environment for the next 72 h, and the SHIPS model Rapid
Intensification Index shows better than a 50 percent chance of a
35-kt increase in strength in the next 24 hours and a 45-kt
increase in 36 h.  Based on this, the intensity forecast calls for
36 h more of rapid strengthening.  Given the lack of negative
factors, except for the possibility of eyewall replacement cycles,
the new intensity forecast could still be conservative even though
it lies above the intensity guidance.  After 72 h, Fernanda should
encounter decreasing sea surface temperatures and drier air, and
this is expected to cause a steady weakening.  The new intensity
forecast is again increased considerably over the previous forecast
during the first 36 h, and it is decreased below for previous
forecast at 120 h.


FORECAST POSITIONS AND MAX WINDS

INIT  13/2100Z 11.2N 116.0W   70 KT  80 MPH
 12H  14/0600Z 11.1N 117.5W   85 KT 100 MPH
 24H  14/1800Z 10.9N 119.4W  100 KT 115 MPH
 36H  15/0600Z 10.9N 121.3W  115 KT 130 MPH
 48H  15/1800Z 11.3N 123.5W  120 KT 140 MPH
 72H  16/1800Z 12.5N 128.0W  125 KT 145 MPH
 96H  17/1800Z 14.0N 132.5W  115 KT 130 MPH
120H  18/1800Z 15.5N 136.0W   95 KT 110 MPH

$$
Forecaster Beven

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