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Tropical Storm FERNANDA


Tropical Storm Fernanda Discussion Number   4
NWS National Hurricane Center Miami FL       EP062017
300 PM MDT Wed Jul 12 2017

Fernanda has changed little in organization since the last
advisory, as the center continues to be near the northeastern edge
of the central convection and outer bands persist in the
southwestern semicircle.  Recent scatterometer data indicated
maximum winds near 35 kt, and that remains the initial intensity
based on the scatterometer and various satellite intensity
estimates.  The scatterometer data also showed the Fernanda is
currently a small cyclone, with tropical-storm-force winds
extending no more than 20 n mi from the center.

The initial motion is now 265/8. Deep-layer ridging north of the
cyclone is steering it a little south of due west, and the ridge is
expected to strengthen and build westward during the next several
days.  Thus, a westward or south of westward motion is likely for
the first 72 h.  After that, Fernanda should approach a weakness in
the ridge caused by a mid- to upper-level trough over the central
Pacific, and in response it is expected to turn west-northwestward
by 120 h.  The new forecast track is again similar to, but a little
south of the previous track.  It lies a little north of the
consensus models through 72 h and south of them at 96-120 h.

The cyclone is still feeling the effects of 10-15 kt of vertical
wind shear at this time.  The large-scale models continue to
forecast the shear to subside over the next 24 h or so and then
remain light through the remainder of the forecast period.  That,
combined with 28-29C sea surface temperatures along the first 96 h
of the forecast track, should allow the system to intensify.  After
96 h, the expected more northward motion would bring Fernanda over
decreasing seas surface temperatures, which would likely stop
intensification.  The new forecast is again similar to the previous
forecast and is in best agreement with the intensity consensus.
There remains a possibility that rapid intensification could occur
after the shear subsides.


INIT  12/2100Z 11.8N 112.2W   35 KT  40 MPH
 12H  13/0600Z 11.8N 113.5W   40 KT  45 MPH
 24H  13/1800Z 11.7N 115.5W   50 KT  60 MPH
 36H  14/0600Z 11.6N 117.5W   60 KT  70 MPH
 48H  14/1800Z 11.5N 119.5W   70 KT  80 MPH
 72H  15/1800Z 11.5N 124.0W   90 KT 105 MPH
 96H  16/1800Z 12.0N 128.5W   95 KT 110 MPH
120H  17/1800Z 13.0N 133.0W   95 KT 110 MPH

Forecaster Beven