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Hurricane Walaka Discussion Number  20
NWS Central Pacific Hurricane Center Honolulu HI   CP012018
500 AM HST Thu Oct 04 2018
 
Walaka's partially exposed low-level circulation center (LLCC) is 
evident southwest of an area of deep convection. Strong vertical
wind shear from the southwest is likely responsible for this. As a
result of this persistent weakening, the latest subjective Dvorak
current intensity estimates were 5.0/90 kt from JTWC and PHFO, and
4.5/77 kt from SAB. The latest UW-CIMSS ADT estimate around 1330Z
has lowered to 5.2/95 kt. Therefore, the initial intensity for this
advisory is 95 kt.
 
Walaka's initial motion for this advisory is 360/17 kt. The track
forecast guidance remains rather tightly clustered. We have had to
make some minor adjustments in the latest track forecast compared
with the previous advisory during the 12 to 48 hour time periods.
This is primarily due to the way the models are handling Walaka's
interaction with a deep layer low now centered near 29N 171W. Since
there remains a great deal of uncertainty about how warm core Walaka
will respond to the close encounter with this baroclinic feature, we
are assuming it will survive the event intact. So with this
uncertainty in mind, Walaka is expected to move northward at a
slower speed within the next 12 hours, followed by a turn toward the
north-northwest between 12 and 24 hours. After that, again assuming
Walaka is a viable system, it is expected to turn toward the
north-northeast between the 24 and 36 hour time periods. An
accelerating north-northeast motion is forecast during the 48 to 72
hour time periods.
 
With continued strong vertical wind shear , sea surface
temperatures (SST) dropping below 27 degrees C, and reduced ocean
heating content today, Walaka will likely experience a rather rapid
weakening trend. By tonight, the guidance continues to suggest the
vertical wind shear may relax somewhat. However, water temperatures
will become a limiting factor, since the SST would likely cool to
24-25 degrees C. As was mentioned above, we are still not certain
how the interaction with the cold core low will affect Walaka.
Assuming it survives intact as a warm core system, we continue to
maintain it as a tropical storm between 36 and 48 hours. After that,
extratropical transition will likely occur, so that Walaka will
likely be an extratropical gale low by day 3. 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  04/1500Z 26.8N 166.5W   95 KT 110 MPH
 12H  05/0000Z 29.4N 166.8W   80 KT  90 MPH
 24H  05/1200Z 31.8N 167.2W   65 KT  75 MPH
 36H  06/0000Z 34.4N 165.8W   55 KT  65 MPH
 48H  06/1200Z 38.9N 162.2W   50 KT  60 MPH
 72H  07/1200Z 51.0N 151.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 96H  08/1200Z...DISSIPATED
 
$$
Forecaster Houston
 
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