ZCZC HFOTCDCP1 ALL TTAA00 PHFO DDHHMM Hurricane Walaka Discussion Number 19 NWS Central Pacific Hurricane Center Honolulu HI CP012018 1100 PM HST Wed Oct 03 2018 Walaka's appearance has continued to degrade this evening, with no signs of an eye. Strong vertical wind shear is likely to blame for this. Fortunately, a plethora of microwave images were available from the FNMOC and NRL web sites earlier this evening. These passes, which were useful for determining the location of the low-level circulation center (LLCC), indicated the eyewall structure appeared to remain somewhat intact, although there has been some degradation in the southeastern quadrant. As a result of this continued weakening, the latest subjective Dvorak current intensity estimates were 5.5/102 kt from JTWC and PHFO, and 4.5/77 kt from SAB. The latest UW-CIMSS ADT estimate was 5.8/110 kt. The initial intensity for this advisory is 110 kt. Walaka's initial motion for this advisory is 025/19 kt. The track forecast guidance remains tightly clustered, but it has shifted slightly to the left during the 12 to 36 hour time periods. Therefore, we have had to make some minor adjustments in the current 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 the much anticipated interaction with a deep layer low centered near 30N 170W this evening. Since there is 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, we have Walaka moving 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 by the 36 hour time period. An accelerating north-northeast motion is forecast during the 48 to 72 hour time periods. With continued strong vertical wind shear into Thursday and sea surface temperatures (SST) dropping to around 27 degrees C later tonight, Walaka will likely experience a more rapid weakening trend through early Thursday morning. We continue to weaken it below major hurricane status within 12 hours. By late Thursday, the guidance continues to suggest the vertical wind shear may relax somewhat. However, water temperatures and ocean heat content will become limiting factors, since 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, 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 low by day 3. Note that the latest intensity forecast was adjusted slightly up from the previous package during the 36 to 72 hour time periods. This is more in line with the latest GFS and ECMWF output. FORECAST POSITIONS AND MAX WINDS INIT 04/0900Z 24.8N 166.7W 110 KT 125 MPH 12H 04/1800Z 27.5N 166.5W 90 KT 105 MPH 24H 05/0600Z 30.3N 167.2W 75 KT 85 MPH 36H 05/1800Z 32.5N 166.6W 60 KT 70 MPH 48H 06/0600Z 35.4N 164.2W 55 KT 65 MPH 72H 07/0600Z 46.0N 156.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 08/0600Z...DISSIPATED $$ Forecaster Houston NNNN