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Hurricane Fernanda Discussion Number  19
NWS National Hurricane Center Miami FL       EP062017
800 AM PDT Sun Jul 16 2017

It appears that Fernanda completed an eyewall replacement overnight
with an 1109 UTC SSMI microwave overpass showing evidence of a
single eyewall with a diameter of about 15-20 n mi.  This may
have led to the restrengthening that was indicated in the previous
advisory.  Since that time, the eye has remained very distinct in
infrared satellite pictures but the convective cloud tops have
warmed a little this morning.  Although Dvorak data T-numbers have
decreased slightly, the initial intensity remains at 115 kt, in
agreement with the Dvorak CI-numbers from TAFB and SAB.

Fernanda is forecast to remain over warm water and within a low
shear environment during the next 24 hours. During that time,
additional eyewall replacement cycles could occur leading to some
fluctuations in intensity.  Since the timing of eyewall replacement
cycles are difficult to predict, little change in intensity
is indicated in the NHC forecast through Monday morning.  After that
time, Fernando is forecast to begin moving over cooler waters which
should initiate gradual weakening.  The rate of weakening is
expected to increase later in the period when Fernanda moves over
SSTs of 25-26C and westerly shear increases.  The NHC intensity
forecast is similar to the previous advisory and is close to the
various consensus aids.

The hurricane is moving west-northwestward at about 11 kt. The
track forecast reasoning remains unchanged yet again. Fernanda is
expected to remain on a west-northwestward heading during the next
3 days while it is steered by a deep layer ridge to the north of
the hurricane.  A westward turn is foreast later in the period, as
the ridge builds westward when a trough northeast of the Hawaiian
Islands lifts out. The track guidance remains in very good
agreement and the updated NHC track is similar to the previous
advisory.

FORECAST POSITIONS AND MAX WINDS

INIT  16/1500Z 12.4N 127.4W  115 KT 130 MPH
 12H  17/0000Z 13.0N 129.0W  115 KT 130 MPH
 24H  17/1200Z 13.8N 130.9W  110 KT 125 MPH
 36H  18/0000Z 14.7N 132.6W  100 KT 115 MPH
 48H  18/1200Z 15.5N 134.0W   90 KT 105 MPH
 72H  19/1200Z 16.9N 136.5W   65 KT  75 MPH
 96H  20/1200Z 17.5N 139.8W   45 KT  50 MPH
120H  21/1200Z 17.9N 143.3W   35 KT  40 MPH

$$
Forecaster Brown

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