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Tropical Storm Fernanda Discussion Number  40
NWS Central Pacific Hurricane Center Honolulu HI   EP062017
1100 AM HST Fri Jul 21 2017
 
Fernanda presents poorly in satellite imagery. Deep convection
remains within the northeast quadrant of Fernanda's low level
circulation center (LLCC), ranging from 40 to 110 nm, as this system
feels the effects of strong southwesterly shear. Subjective Dvorak
satellite intensity estimates range from 25 kt, from SAB, to 35 kt,
from PHFO. UW-CIMSS provided an ADT intensity of 25 kt. It is too
early for a timely ASCAT pass, so we will assign a potentially
generous 35 kt as the initial system intensity in keeping with the
overall poor appearance and continued weakening trend.

Initial motion is 280/07kt, representing a bit of slowing over the
past 12 hours, as Fernanda moves westward along the southern flank
of the subtropical ridge. A weakness in the ridge west of 160W
continues to allow Fernanda to gain latitude, although quite
slowly. Track quidance, once the unrepresentitive GFS and its
associated blends are removed, is rather tight, depicting a shallow
system moving generally westward to west northwestward within low
level steering flow. The forecast track closely follows the
previous one, but is nudged ever so slightly to the left at 24 and
36 hours to account for the ECMWF leftward shift through those
times. The 48 hour forecast is almost unchanged, with system
dissipation expected afterward. Note that on this forecast track,
Fernanda is not forecast to reach the longitude of the main Hawaiian
Islands as an intact tropical system.

Fernanda remains in an unfavorable environment, with sea surface
temperatures around 25C and between 30 and 35 knots of southwesterly
shear. These conditions will persist along the forecast track. As a
result, the forecast is for slow and steady weakening, with Fernanda
expected to become a tropical depression in 12 hours, a remnant low
at 36 hours, then dissipate after 48 hours.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  21/2100Z 18.7N 144.3W   35 KT  40 MPH
 12H  22/0600Z 19.0N 145.6W   30 KT  35 MPH
 24H  22/1800Z 19.6N 147.5W   30 KT  35 MPH
 36H  23/0600Z 20.2N 149.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  23/1800Z 20.9N 151.8W   20 KT  25 MPH...POST-TROP/REMNT LOW
 72H  24/1800Z...DISSIPATED
 
$$
Forecaster Powell
 
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