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Hurricane WALAKA

Hurricane Walaka Discussion Number  12
NWS Central Pacific Hurricane Center Honolulu HI   CP012018
500 AM HST Tue Oct 02 2018
The satellite presentation of Walaka which was being degraded by an
eye wall replacement cycle overnight, has just begun to improve with
a ring of deep convection beginning to once again encircle the
well defined eye, which could be a sign that the eyewall replacement
cycle is getting ready to complete. The latest intensity estimates
from PHFO, SAB, JTWC were 6.5 (127 knots) while the ADT held at 6.6
(130 knots). Based on constraints likely holding the intensity of
Walaka too low Monday afternoon, have only reduced the initial
intensity slightly with this advisory to 135 knots. The initial
motion was set at 350/09 knots.

A deep north Pacific upper level low in the vicinity of 30N 170W
will draw Walaka northward over the next several days, before
another sharp upper trough shifting across the north Pacific picks
the tropical cyclone up and shifts it off to the northeast Friday
night and Saturday. Overall the guidance envelope remains fairly
tightly clustered through the forecast period. The official forecast
remains very close to that of the previous advisory and is fairly
well aligned with the latest GFEX, TVCN, HCCA consensus guidance.

The environment surrounding Walaka remains conducive for additional
intensification during the next 24 hours. The tropical cyclone will
remain within a deep moist airmass with low vertical wind shear,
high ocean heat content and sea surface temperatures between 84 to
86 Fahrenheit. Eyewall replacement cycles could lead to some
fluctuations in intensity through this time frame, so the intensity
forecast shows little intensity change through 24 hours. Beyond 24
hours, the combination of increasing vertical wind shear, drier
mid-level air entraining into the cyclone, sea surface temperatures
becoming marginal and even unfavorable, along with interaction with
the deep upper level low should result in steady and even rapid
weakening of Walaka. As a result, the intensity forecast calls for
Walaka to begin weakening on Wednesday, with rapid weakening then
continuing through the end of the forecast period. The official
intensity forecast was adjusted downward slightly, but remains above
all guidance through 36 hours before trending closer to a blend of
the statistical and dynamical models thereafter. Walaka is expected
to become an post-tropical/extra-tropical low by 120 hours.

The forecast track will take Walaka near Johnston Island later
today, with hurricane conditions expected this afternoon and this
evening. Therefore a Hurricane Warning remains in effect for this
location. The forecast track also takes the hurricane across the
Papahanaumokuakea Marine National Monument between French Frigate
Shoals and Laysan Island late Wednesday. Therefore, a Hurricane
Watch remains in effect for the region from Nihoa to Maro Reef.
INIT  02/1500Z 14.7N 170.0W  135 KT 155 MPH
 12H  03/0000Z 16.2N 170.2W  135 KT 155 MPH
 24H  03/1200Z 18.9N 169.7W  135 KT 155 MPH
 36H  04/0000Z 22.3N 168.4W  120 KT 140 MPH
 48H  04/1200Z 26.2N 167.4W  100 KT 115 MPH
 72H  05/1200Z 30.5N 168.0W   75 KT  85 MPH
 96H  06/1200Z 33.0N 164.0W   60 KT  70 MPH
120H  07/1200Z 41.0N 157.5W   50 KT  60 MPH...POST-TROP/EXTRATROP
Forecaster Jelsema