ZCZC HFOTCDCP1 ALL TTAA00 PHFO DDHHMM 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 120. FORECAST POSITIONS AND MAX WINDS 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 NNNN
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