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Tropical Storm Fernanda Discussion Number  42
NWS Central Pacific Hurricane Center Honolulu HI   EP062017
1100 PM HST Fri Jul 21 2017

The satellite presentation of Fernanda has degraded since the
previous advisory, with cloud tops warming to the northeast of the
exposed low level circulation center (LLCC). The latest subjective
Dvorak intensity estimates came in at 25 and 30 knots from SAB and
PHFO respectively, with the ADT intensity from UW-CIMSS coming in
at 30 knots as well. However, a late arriving ASCAT pass from
22/0640Z, indicated that a small area of 35 knot winds remain
present to the north of the LLCC, and thus Fernanda is a
minimal Tropical Storm. This does not mean that the system has
intensified since the previous advisory, but that the storm was
slightly stronger than previously thought.

The initial motion for this advisory is 285/7 kt, representing a
slight decrease in the west-northwestward motion since the previous
advisory. The GFS continues to be the northern outlier solution,
with the ECMWF solution the farthest to the south. Hostile
environmental conditions will remain over Fernanda over the next
couple of days, keeping the system shallow with the track more
influenced by the low level trade wind flow. As a result, the
forecast track for this advisory will remain very close to that of
the previous advisory, keeping it to the south of the GFEX and TVCN
consensus aids that are likely too far north due to the influence
from the outlier GFS solution. A general motion toward the
west-northwest with an increase in forward speed is expected through
system dissipation.

Fernanda remains in an unfavorable environment with sea surface
temperatures around 25C, very dry air aloft as evident in water
vapor imagery, as well as strong southwesterly shear of around 30
knots. Strong shear of 25 to 35 kt, very dry air aloft, and
unfavorable sea surface temperatures hovering between 25 and 26C
are forecast to persist through the forecast period. As a result,
the forecast will continue to show slow and steady weakening, with
Fernanda expected to become a Tropical Depression in 12 hours, a
remnant low in 24 hours, with dissipation forecast after 48 hours.


FORECAST POSITIONS AND MAX WINDS

INIT  22/0900Z 19.0N 145.4W   35 KT  40 MPH
 12H  22/1800Z 19.4N 146.8W   30 KT  35 MPH
 24H  23/0600Z 20.0N 149.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
 36H  23/1800Z 20.4N 151.2W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  24/0600Z 20.6N 154.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  25/0600Z...DISSIPATED

$$
Forecaster Jelsema




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