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Post-Tropical Cyclone Walaka Discussion Number  28
NWS Central Pacific Hurricane Center Honolulu HI   CP012018
500 AM HST Sat Oct 06 2018
 
Walaka's low-level circulation center (LLCC) remains completely
devoid of deep convection early this morning.  The last few
thunderstorms associated with the system are slightly more than 
90 n mi southeast of the exposed LLCC. ASCAT passes over Walaka at
0735Z and 0838Z showed the system was stronger than expected, with
surface wind speeds up to 45 kt. It was also apparent the center of
the system was becoming elongated instead of circular. In addition,
the wind field was highly asymmetric, with the strongest winds in a
broad area covering the southeastern semicircle, while the winds
were much weaker over most of the northwestern semicircle. Based on
this evidence, Walaka has already transitioned to an extratropical
gale low this morning. The initial intensity for this advisory is
45 kt due to the ASCAT data from last evening.
 
The initial motion for this advisory is 035/23 kt. Walaka is being
steered by the deep southwesterly flow associated with an advancing
upper-level trough. As a result, it will likely continue to move
toward the northeast or north-northeast at an increasing forward
speed this weekend. The latest track forecast has been adjusted
slightly to the left compared with the previous advisory package.
This follows a blend of the track guidance based on the latest
operational runs and the ensemble means from the GFS and ECMWF
models.
 
The baroclinic processes driving Walaka's new life as an
extratropical system will likely maintain an area of gale force
winds over the southeastern semicircle during the next 36 hours.
The latest intensity forecast has been adjusted up compared with
the previous advisory package to account for these gales. This
intensity forecast is based on a blend of the most recent GFS and
ECMWF models, which are in good agreement through 24 hours. The
ECMWF maintains 35 kt winds for the 36 hour time period, while the
GFS output indicates the winds may drop below gale force by that
time. Both models continue to insist the system will be absorbed by
a larger extratropical low after 36 hours. Therefore, dissipation
will occur by the 48 hour time period.
 
This is the last Tropical Cyclone Discussion issued by the Central
Pacific Hurricane Center on this system.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  06/1500Z 36.2N 163.5W   45 KT  50 MPH...POST-TROPICAL
 12H  07/0000Z 41.0N 160.5W   40 KT  45 MPH...POST-TROP/EXTRATROP
 24H  07/1200Z 48.0N 154.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
 36H  08/0000Z 55.0N 148.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
 48H  08/1200Z...DISSIPATED
 
$$
Forecaster Houston
 
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