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Tropical Storm Fernanda Discussion Number  37
NWS Central Pacific Hurricane Center Honolulu HI   EP062017
500 PM HST Thu Jul 20 2017

Most of the deep convection near the center of Fernanda has
dissipated leaving an exposed low level circulation center
surrounded by mostly low- and mid-level clouds. The remaining
thunderstorms are confined to an outer rainband more than 60 nm
north of the center. The initial intensity is 45 kt which is
slightly weaker than the previous advisory. This may be conservative
but an ASCAT pass from 1936 UTC sampled the northwestern portion of
the circulation and found 40 kt. Subjective Dvorak estimates from
PHFO and SAB came in at 35 kt but this may be too aggressive a drop
at this time.

The initial motion for this package is 280/10 kt with steering
increasingly dictated by the low level flow. The main dynamical
aids show a fair amount of spread. The GFS, and to a lesser
degree HWRF, continue to hold on to a stronger and deeper system
which results in a more northwestward track. This doesn't appear
to be reasonable given the environmental circumstances. Thus, the
forecast track leans more toward the ECMWF solution and is close to
the previous forecast, keeping Fernanda on a general westward to
west-northwestward motion through the forecast period. 

Fernanda is tracking over waters near 25C. Along the forecast track,
sea surface temperature are to remain in the 25C to 26C range. The
cyclone is also expected to stay within strong vertical shear
conditions of about 25 to 35 kt through the next 3 days.
Although some deep convection may occasionally flare up near
the center, the more likely outcome under these environmental
conditions is for Fernanda to continue to weaken and eventually
dissipate. This expectation is consistent with the SHIPS
guidance. The forecast calls for continued weakening with Fernanda
becoming a remnant low during the next 24 to 36 hours, then opening
up to a trough after 72 hours.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  21/0300Z 18.4N 141.4W   45 KT  50 MPH
 12H  21/1200Z 18.8N 142.9W   35 KT  40 MPH
 24H  22/0000Z 19.3N 144.8W   30 KT  35 MPH
 36H  22/1200Z 19.9N 146.6W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  23/0000Z 20.5N 148.4W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  24/0000Z 21.8N 153.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  25/0000Z...DISSIPATED
 
$$
Forecaster Kodama
 
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