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Hurricane WALAKA

Hurricane Walaka Discussion Number   8
NWS Central Pacific Hurricane Center Honolulu HI   CP012018
500 AM HST Mon Oct 01 2018
The satellite presentation of Walaka has improved significantly 
overnight as the cyclone continues to rapidly intensify. The well 
defined eye is surrounded by a large ring of -70 to -85C cloud
tops, and continues to show excellent outflow in all quadrants as
evident in geostationary satellite animations. Additionally, large
deep convective banding features are present on both the east and
west side of Walaka early this morning. The latest intensity
estimates came in at 5.5 (102 knots) from PHFO, SAB, and JTWC, while
the UW-CIMSS ADT was 5.4 (100 knots). As of 01/14Z, raw DT numbers
are as high as 7.0 (140 knots), but need to be held down
due to intensification constraints. Based on this data along with
the continued improvement in the appearance and organization, the 
initial intensity of Walaka for this advisory was increased to 110 
knots, making it 5 knots short of category 4 status. The initial 
motion was set at 295/09 knots.

Walaka is beginning to round the southwest periphery of a large 
subtropical ridge this morning and is currently moving toward the 
west-northwest. A turn toward the northwest is expected later today 
as a deep north Pacific upper trough digs southward in the vicinity 
of 30N 170W and further erodes the western end of the subtropical 
ridge. 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, with a turn back toward 
the northeast expected Friday night. The official track forecast
was changed very little from the previous advisory and remains
in close proximity to the tightly clustered HCCA, TVCN, and GFEX
consensus guidance.

The environment surrounding Walaka remains very conducive for 
additional intensification during the next 36 hours and possibly 
even a bit longer. Today through Tuesday, the tropical cyclone will
remain within a deep moist airmass, with vertical wind shear
forecast to remain around 10 knots, and sea surface temperatures
holding in the 84 to 86 Fahrenheit range. As a result, additional
rapid intensification is expected today into tonight, with the
cyclone then forecast to level off late tonight through Tuesday
night. Given the environment surrounding the system, the intensity
forecast brings Walaka up to category 5 intensity tonight, and is
slightly above the intensity guidance which doesn't explicitly
indicate Walaka will reach category 5 intensity. There is the
potential that Walaka could intensify even more than currently
forecast, but due to eyewall replacement cycles likely leading to
some fluctuation in intensity, the forecast was held nearly steady
from late tonight through Tuesday night. Vertical wind shear is
expected to steadily increase Wednesday and Wednesday night as
Walaka approaches and begins to interact with the deep upper level
trough over the north-central Pacific, with sea surface temperatures
dropping off during this time as well. The intensity forecast
calls for rapid weakening beginning beyond 48 hours, with this
weakening trend expected to continue through the end of the forecast
period. The official intensity forecast has been increased from the
previous advisory and is slightly higher than all intensity guidance
through 36 hours, then falls more closely in line with a blend of
the statistical and dynamical guidance for forecast hour 72 through
INIT  01/1500Z 12.3N 168.3W  110 KT 125 MPH
 12H  02/0000Z 13.1N 169.4W  130 KT 150 MPH
 24H  02/1200Z 14.5N 170.4W  140 KT 160 MPH
 36H  03/0000Z 16.4N 170.7W  140 KT 160 MPH
 48H  03/1200Z 18.9N 170.1W  135 KT 155 MPH
 72H  04/1200Z 25.0N 167.5W  100 KT 115 MPH
 96H  05/1200Z 29.5N 167.0W   75 KT  85 MPH
120H  06/1200Z 33.0N 164.0W   60 KT  70 MPH
Forecaster Jelsema