Tropical Storm FERNANDA (Text)


Tropical Storm Fernanda Discussion Number   6
NWS National Hurricane Center Miami FL       EP062017
300 AM MDT Thu Jul 13 2017

Fixes off of recent ASCAT data indicate that Fernanda's center is
now fully embedded beneath the convective canopy, and cloud tops
are as cold as -85 deg C.  The improved structure is translating
into stronger surface winds, with the ASCAT passes showing that the
initial intensity is now 45 kt.

The ASCAT data showed that Fernanda's center is moving south of due
west, and the motion estimate is 265/9 kt.  Deep-layer ridging to
the north of the cyclone is expected to strengthen and build
westward, which should keep Fernanda on a west to south-of-due-west
trajectory for the next 3 days.  The ridge then narrows and weakens
a bit on days 4 and 5, which should allow Fernanda to gradually gain
some latitude by the end of the forecast period.  The recent trend
of the track guidance shifting south has continued, and the updated
NHC track forecast has therefore been shifted south of the previous
forecast during the first 48 hours.  After that time, the models are
then suggesting that Fernanda's track may take a more pronounced
poleward bend, and the new NHC forecast is therefore a little
northeast of the previous forecast on days 4 and 5.

Northeasterly shear affecting Fernanda has weakened as expected,
and it's now analyzed to be about 10 kt.  The shear is forecast to
diminish further, and it should generally be below 10 kt for the
remainder of the forecast period.  In addition, Fernanda is
currently moving over a warm pool where sea surface temperatures
are about 29 deg C.  This low-shear, high-SST environment should
spark a significant intensification trend in the coming days.
HCCA, the Florida State Superensemble (FSSE), and the COAMPS-TC
model are all quite aggressive, showing Fernanda becoming a major
hurricane just after 48 hours and continuing to strengthen through
days 3 and 4.  This scenario is supported by the SHIPS RI guidance,
which gives a 50/50 chance of Fernanda reaching major hurricane
strength in 48 hours.  Based on these models, the NHC intensity
forecast has been bumped upward, and it generally lies near a blend
of HCCA, FSSE, and the ICON intensity consensus.


INIT  13/0900Z 11.7N 114.1W   45 KT  50 MPH
 12H  13/1800Z 11.5N 115.5W   55 KT  65 MPH
 24H  14/0600Z 11.2N 117.4W   65 KT  75 MPH
 36H  14/1800Z 10.9N 119.3W   80 KT  90 MPH
 48H  15/0600Z 10.9N 121.4W   95 KT 110 MPH
 72H  16/0600Z 11.6N 125.9W  110 KT 125 MPH
 96H  17/0600Z 12.8N 130.2W  115 KT 130 MPH
120H  18/0600Z 14.0N 134.0W  105 KT 120 MPH

Forecaster Berg


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Page last modified: Sunday, 31-Dec-2017 12:10:07 UTC