| http://www.prh.noaa.gov/cphc/tcpages/archive/2018/TCDCP2.EP142018.041.201808242110 Hurricane Lane Discussion Number 41 NWS Central Pacific Hurricane Center Honolulu HI EP142018 1100 AM HST Fri Aug 24 2018 Lane continues to struggle against 30 to 40 kt of southwesterly shear as analyzed by the UW-CIMSS shear analysis. The CDO continues to be very asymmetric and elliptical. Radar, lightning data, and 1645z Windsat pass indicated that the active convection has been shunted to the northwest through north of the low level circulation center, indicating that the core of the tropical cyclone is getting torn apart by the shear. Subjective current intensity estimates were unanimous at 5.0, and CIMSS-ADT had 5.1. The initial intensity was lowered to 90 kt for this advisory. The initial motion estimate a rather uncertain 360/4. The changes to Lane's structure make the near term track forecast very difficult, as the steering layer will be rapidly evolving in the short term. The proximity to island terrain makes the steering flow even more complex, at least until the vortex completely separates from the persistent convection as a shallow low level circulation. Until then, the motion is likely to be somewhat slow and erratic. The reliable track guidance suggests a slow north or north-northeastward drift for the next 12 hours, followed by an abrupt shift toward the west at some point afterward. The consensus models show a general westward motion from 24 through 96 hours, then turning more toward the northwest. The only significant change to the track forecast during this time was to slow Lane's forward motion. If anything is left of Lane between 96 and 120 hours, the low level circulation may gain latitude and try to merge with a large upper low over the Northwestern Hawaiian Islands. As long as Lane can maintain central deep convection, the weakening trend will remain more gradual. More rapid weakening will commence within 12 to 24 hours, once the convection is no longer able to remain anchored to the low level circulation center. All of the guidance indicates rather rapid weakening in the near term, and our forecast agrees though is at the high end of the guidance in deference to Lane's persistent core. Although the current forecast retains Lane as a tropical cyclone through 5 days, it's very possible that Lane will not last that long as the low level circulation crosses underneath a band of very strong wind shear. KEY MESSAGES: 1. One should not interpret the forecast westward turn south of the islands as a lower threat to the islands. If Lane retains central core convection longer than anticipated, the westward turn would happen later, which could bring hurricane conditions to Maui County or Oahu. This solution is still plausible at this time. Regardless of whether Lane makes landfall, severe impacts are still possible and the effects can extend far to the north and east of the center of Lane. 2. Lane will remain dangerously close to the central Hawaiian Islands as a hurricane today into tonight bringing damaging winds to some areas. Terrain effects can cause strong localized acceleration of the wind through gaps and where winds blow downslope. These acceleration areas will shift with time as Lane passes near or over the islands. Winds will also be stronger at the upper floors of high rise buildings. 3. The slow movement of Lane greatly increases the threat for prolonged heavy rainfall. This is expected to lead to major flash flooding and landslides in some areas. 4. Life-threatening and damaging surf can be expected along exposed shorelines with localized storm surge exacerbating the impacts of a prolonged period of damaging surf. The prolonged period of large surf will also likely produce severe beach erosion. FORECAST POSITIONS AND MAX WINDS INIT 24/2100Z 19.1N 157.9W 90 KT 105 MPH 12H 25/0600Z 19.7N 157.7W 75 KT 85 MPH 24H 25/1800Z 20.2N 158.1W 65 KT 75 MPH 36H 26/0600Z 20.2N 159.4W 55 KT 65 MPH 48H 26/1800Z 20.1N 160.8W 45 KT 50 MPH 72H 27/1800Z 20.4N 163.4W 35 KT 40 MPH 96H 28/1800Z 22.4N 165.7W 30 KT 35 MPH 120H 29/1800Z 26.7N 168.5W 30 KT 35 MPH $$ Forecaster R Ballard |