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Tropical Storm Fernanda Discussion Number  38
NWS Central Pacific Hurricane Center Honolulu HI   EP062017
1100 PM HST Thu Jul 20 2017
 
Deep convection has flared up this evening to the northeast of the
low level circulation center of Fernanda. The latest subjective
Dvorak intensity estimates from PHFO and SAB came in at 35 and 30
knots respectively, likely too low given the slow spin down time of
these systems. Given the improvement in appearance of Fernanda
since the previous advisory, the initial intensity will be held at
45 knots for this package. 

The initial motion for this advisory is 280/10 kt. The spread
between the reliable guidance remains large. The GFS continues
to show a stronger and deeper system tracking off to the
west-northwest for the next 12 hours and then toward the northwest
for the next several days thereafter around the southwestern 
periphery of a strong sub-tropical ridge. The ECMWF and HWRF on the
other hand, show a more shallow system steered along primarily by
the low level trade wind flow. Given the unfavorable environmental
conditions, the forecast track is very close to the previous
official forecast, and closely in line with the ECMWF and HWRF
solutions. As a result, the forecast track takes Fernanda off to
the west-northwest through the forecast period.

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 remain over the system 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 to 24 hours, a remnant low in 24 to 36 hours, then dissipating
after 72 hours.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  21/0900Z 18.4N 142.5W   45 KT  50 MPH
 12H  21/1800Z 18.9N 144.0W   35 KT  40 MPH
 24H  22/0600Z 19.5N 145.9W   30 KT  35 MPH
 36H  22/1800Z 20.1N 147.7W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  23/0600Z 20.7N 150.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  24/0600Z 22.0N 155.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  25/0600Z...DISSIPATED
 
$$
Forecaster Jelsema
 
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