Hurricane Fernanda Discussion Number 31
NWS National Hurricane Center Miami FL EP062017
800 AM PDT Wed Jul 19 2017
While there are still occasional glimpses of the eye in infrared
imagery, the convective cloud pattern of Fernanda continues to
slowly decay. The initial intensity is thus reduced a little more,
to 75 kt, based on a blend of various satellite intensity
estimates. Water vapor imagery shows that the outflow is becoming
restricted in the southwestern quadrant, which is a reflection of
10-15 kt of southwesterly vertical shear affecting the cyclone.
The initial motion is 310/7. Fernanda is expected to turn
west-northwest later today and continue this motion through 72 h as
it is steered by a strong low- to mid-level ridge to the north.
This ridge is forecast to persist after 72 h. However, the
guidance becomes more divergent during that time, likely due to how
quickly the various large-scale models weaken Fernanda. The NAVGEM
and Canadian models, which weaken the cyclone quickly, show a
generally westward motion of the remnants. The GFS and the HWRF,
which maintain a stronger vortex, show a more northerly motion on
the right side of the guidance envelope. The ECMWF is between these
extremes, and this part of new track forecast is a little to the
north of the ECMWF and a little south of the model consensus.
Overall, the new forecast is little changed through 72 h, then
nudged north of the previous forecast thereafter.
Fernanda is expected to steadily weaken through the forecast period
due to various combinations of cool sea surface temperatures,
southwesterly to southerly shear, and dry air entrainment. Thus,
the new forecast again follows the trend of the previous advisory
and calls for Fernanda to weaken to a tropical storm in less than 24
h, a post-tropical low by 72 h, and a remnant low by 96 h. The new
forecast is little changed from the previous forecast and lies
close to the intensity consensus. It should be noted that the GFS
and ECMWF show the possibility that Fernanda could interact with an
upper-level trough north of the Hawaiian Islands in a way that
could prolong its life as a tropical cyclone. Currently, the
confidence in this happening is too low to justify a change to the
forecast.
FORECAST POSITIONS AND MAX WINDS
INIT 19/1500Z 17.4N 135.5W 75 KT 85 MPH
12H 20/0000Z 17.9N 136.5W 65 KT 75 MPH
24H 20/1200Z 18.5N 138.0W 55 KT 65 MPH
36H 21/0000Z 19.0N 139.6W 45 KT 50 MPH
48H 21/1200Z 19.5N 141.3W 40 KT 45 MPH
72H 22/1200Z 20.5N 144.5W 35 KT 40 MPH...POST-TROPICAL
96H 23/1200Z 22.0N 149.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 24/1200Z 23.0N 153.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
$$
Forecaster Beven
