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Hurricane Fernanda Discussion Number  20
NWS National Hurricane Center Miami FL       EP062017
200 PM PDT Sun Jul 16 2017

Satellite images indicate that the eye of Fernanda, which is about
10 n mi in diameter, is not quite as distinct as it was earlier
today.  The deep convection surrounding the eye is also a little
less symmetric with a few dry slots noted in infrared pictures.  The
initial wind speed is lowered slightly to 110 kt, based on an
average of Dvorak T- and CI-numbers from TAFB, SAB, and ADT values
from CIMSS at the University of Wisconsin.  The hurricane is still
over warm water and in a favorable atmospheric environment, and it
is forecast to remain in those conditions for another day or so.
Therefore, little change in strength is expected in the short term.
After that time, however, cooler waters, drier air, and an increase
in wind shear should cause Fernanda to steadily weaken.  The NHC
intensity forecast is an update of the previous one, and is in
general agreement with the consensus models.

Fernanda continues to move west-northwestward at 10 kt near the
southwestern periphery of a mid-level high pressure system
centered over the southwestern United States.  The track forecast
philosophy remains unchanged from the past several advisories.  A
trough to the northeast of the Hawaiian Islands is expected to erode
the western portion of the ridge during the next few days.  This
pattern change should cause Fernanda to slow down and gain more
latitude than it has in previous days.  The trough is expected
to lift out later in the week allowing the ridge to rebuild to the
the north of the tropical cyclone in about 4 days.  This should
cause Fernanda to turn back toward the west in the 4- to 5-day
period.  The models are in good agreement on this overall
scenario, and the NHC track forecast is near the middle of the
guidance envelope.

The initial wind radii were expanded outward based on a 1835 UTC
ASCAT overpass.

FORECAST POSITIONS AND MAX WINDS

INIT  16/2100Z 12.7N 128.4W  110 KT 125 MPH
 12H  17/0600Z 13.3N 129.8W  110 KT 125 MPH
 24H  17/1800Z 14.2N 131.6W  105 KT 120 MPH
 36H  18/0600Z 15.0N 133.0W   95 KT 110 MPH
 48H  18/1800Z 15.9N 134.2W   85 KT 100 MPH
 72H  19/1800Z 17.0N 136.7W   60 KT  70 MPH
 96H  20/1800Z 17.5N 140.1W   45 KT  50 MPH
120H  21/1800Z 18.0N 144.0W   35 KT  40 MPH

$$
Forecaster Cangialosi

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