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Hurricane Walaka Discussion Number   7
NWS Central Pacific Hurricane Center Honolulu HI   CP012018
1100 PM HST Sun Sep 30 2018
 
Walaka is undergoing rapid intensification this evening, which is 
clearly evident given the large ring of -70 to -85C cloud tops 
surrounding the the well defined eye. Additionally, recent
microwave passes indicate that the organization of the system has
improved significantly, while geostationary satellite animations
show well defined outflow channels in all quadrants. The latest
intensity estimates came in at 5.0 (90 knots) from PHFO and SAB, 4.5
(77 knots) from JTWC, while the UW-CIMSS ADT was 4.2 (70 knots).
Based on the significant improvement in appearance and organization
of Walaka, the initial intensity for this advisory was increased to
90 knots. The initial motion was set at 280/10 knots.

Walaka continues to be steered westward this evening by a 
subtropical ridge to the north of the system, and this motion is 
expected to continue tonight. A turn toward the northwest is 
expected on Monday as a deep north Pacific upper trough digs 
southward in the vicinity of 30N 170W. A turn toward the north is 
then expected on Tuesday, with Walaka continuing on this course 
through Tuesday night with an increase in forward speed. The 
tropical cyclone should then make a turn toward the north-northeast 
Wednesday and Wednesday night as it begins to feel the influence of 
the deep upper level trough. The track guidance then suggests a 
shift back toward the north with a decrease in forward speed 
Thursday through Friday as Walaka interacts with the deep upper 
level trough. The official forecast was nudged slightly to the left 
through 48 hours, then slightly to the right beyond 48 hours, and
is very close to the HCCA, TVCN, and GFEX consensus guidance.

The environment surrounding Walaka remains very conducive for 
additional intensification through 48 hours. The tropical cyclone 
will remain within a deep moist airmass, with vertical wind shear 
forecast to remain around 10 knots or less through 48 hours, and
sea surface temperatures holding in the 84 to 86 Fahrenheit range
during this time. As a result, additional rapid intensification is
expected tonight and Monday, with the cyclone then forecast to level
off just below category 5 status Tuesday and Tuesday night. Given
the environment surrounding the system, intensification to a
category 5 storm is not out of the question, although none of the
intensity guidance explicitly indicate this at this time.
Additionally, Walaka will likely undergo eyewall replacement cycles
which will lead to some fluctuation in intensity. Beyond 48 hours,
vertical wind shear will steadily increase as Walaka approaches and
begins to interact with the deep upper level trough over the
north-central Pacific, with sea surface temperatures dropping off as
well. The intensity forecast shows a gradual weakening by 72 hours,
with rapid weakening then expected beyond 72 hours through the end
of the forecast period. The official intensity forecast has been
increased from the previous advisory and is in line with the high
end of the intensity guidance.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  01/0900Z 11.9N 167.5W   90 KT 105 MPH
 12H  01/1800Z 12.5N 168.7W  115 KT 130 MPH
 24H  02/0600Z 13.5N 169.9W  130 KT 150 MPH
 36H  02/1800Z 15.1N 170.5W  135 KT 155 MPH
 48H  03/0600Z 17.2N 170.5W  135 KT 155 MPH
 72H  04/0600Z 23.3N 168.1W  115 KT 130 MPH
 96H  05/0600Z 28.5N 167.5W   75 KT  85 MPH
120H  06/0600Z 31.0N 166.0W   60 KT  70 MPH
 
$$
Forecaster Jelsema
 
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