FORECAST DISCUSSION

Synopsis

22 Aug 2018 06:51:00 GMT: A strong high pressure ridge far to the north of the Hawaiian Islands will produce breezy winds over the local area ahead of Hurricane Lane. Deep tropical moisture will move up from the south with Lane, spreading increasing rain shower bands and possible thunderstorms over the Big Island by Wednesday morning and reaching Maui by Wednesday afternoon and evening. These shower bands will continue to spread northward across the rest of the state as Lane moves northward. Hurricane Lane will bring damaging winds, dangerous surf, and intense flooding rains to areas within the state of Hawaii from Wednesday through Saturday.

Discussion

22 Aug 2018 06:51:00 GMT: Please note that tropical cyclone operations are in effect. To incorporate the latest forecast information from the Central Pacific Hurricane Center (CPHC), public forecast updates from the Honolulu Forecast Office will be delayed to immediately follow the latest forecast package from CPHC. Tranquil weather conditions across the islands today will become more unsettled and threatening over the next several days as Lane a category 5 Hurricane roughly 370 miles south-southeast of Kona moves northwestward into the Hawaiian Islands. Lane is one of the strongest storms to ever move into the Hawaiian Islands and the current forecast track will bring local impacts of damaging winds and life threatening flooding rain across the state from Wednesday through Saturday. Do not wait until the storm reaches your island, the time to prepare for hurricane impacts is now. As Hurricane Lane moves further northward, deep unstable tropical moisture will spread across the region. Precipitable Water (PW) values will range from 2.0 to 2.5 inches, producing hot and humid weather conditions and widespread convective heavy rain shower bands. This extremely deep moisture will reach the Big Island by Wed morning, Maui county by Wed night, Oahu by Thu, and Kauai by later Thu or Thu night. Once this extreme moisture arrives the heavy rainfall will start to develop quickly with the orographic effects from mountain ranges alone causing flooding threats across the islands with additional forcing from an upper level trough just to the northwest of the islands. Strong winds will develop, based on the latest CPHC forecast, starting over the Big Island as soon as Wednesday afternoon with hurricane force winds developing by Wednesday night. The highest wind threat for the Big Island will start along the western side as strong and gusty down slope winds interact with mountainous terrain. On Maui county, damaging tropical storm force winds could begin as early as late Wednesday night, with dangerous hurricane force winds possible starting on Thursday. Oahu could see damaging winds by Thursday morning, and Kauai by Thursday night. Hurricane Watches could be needed for other areas as Lane draws closer. It's not possible to know which islands will see the worst storm effects right now. The CPHC forecasts continue to show that all islands are at risk from direct effects from the core of Hurricane Lane. Everyone should take this hurricane very seriously and should prepare accordingly. It's also important to expect that there will need to be future adjustments to the track and intensity forecast, particularly with the challenging recurvature forecast that Lane is presenting. Prepare for the worst and hope for the best. The combination of a deep moist unstable layer and strong low level wind shear along and to the east of the track of Lane will make tornadoes and large waterspouts a distinct possibility in the rainbands across the right semicircle of the hurricane. These continue to be included in the TCV and HLS products as an elevated threat from Oahu to the Big Island. Will be able to better refine the threat as Lane approaches. There is a considerable amount of uncertainty in the models as to when the deep moisture in the wake of Lane departs. The ECMWF shows some modest drying out over the weekend, while the GFS and to a lesser extent the NAVGEM maintain high PW over the islands into next week, which could be troublesome on any areas that get excessive rainfall. There may also be some lingering support from upper troughing to the NW. Please consult the latest advisories from CPHC. weather.gov/cphc

Aviation

22 Aug 2018 06:51:00 GMT: The pressure gradient will tighten across the islands as Hurricane Lane approaching from the south while high pressures resides far north. This results in increasing wind speeds over the islands. AIRMET TURB for TEMPO moderate turbulence below eight thousand feet on the leeward side of the mountains will continue through rest of the evening into early Wednesday, with the strongest turbulence on the Big Island. Mainly VFR conditions prevail across the area through rest of the evening into early Wednesday morning, though windward areas will see MVFR ceilings due to passing low clouds. Weather conditions will gradually deteriorate on the Big Island and Maui by Wednesday as Hurricane Lane approaches from the southeast. The best chance for MVFR or even IFR ceilings and VIS conditions will be on these islands, with these spreading to the rest of the islands as rainbands associated with Hurricane Lane reach the area. Otherwise expect VFR conditions for the rest of the state.

Marine

22 Aug 2018 06:51:00 GMT: Marine interests on the Big Island (leeward/southeast coasts) should finalize all preparations for deteriorating conditions by noon Wednesday as Hurricane Lane begins to approach from the south. The earliest potential onset of tropical storm force winds (34 knots or greater) across the waters around South Point and off the coast of Kona will be through the day Wednesday. Once these conditions are realized, it will be too late to prepare. Interests in Maui County and on Oahu should finalize all preparations come Wednesday evening and by noon Thursday for Kauai. The Hurricane Watch currently in place for the waters surrounding Oahu and Maui County will likely become updated to a warning later tonight into Wednesday and expanded across the Kauai waters. Impacts associated with Lane through the rest of the week for the islands will include: hazardous seas, life-threatening surf (warning level), beach erosion, overwash onto vulnerable coastal roadways, and storm surge along exposed coasts/harbors of all islands as Lane passes through. Improving conditions are expected by the end of the upcoming weekend as Lane slowly begins to track away from the island waters. See the latest Oahu Surf Discussion (SRDHFO) for more details on surf and swell from other sources.

HFO Watches/Warnings/Advisories

22 Aug 2018 06:51:00 GMT: Hurricane Watch for Oahu, Molokai, Lanai, Kahoolawe, Maui. Hurricane Watch for Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel. Hurricane Warning for Big Island. Hurricane Warning for Big Island Leeward Waters, Big Island Southeast Waters. Tropical Storm Warning for Big Island Windward Waters. Flash Flood Watch from 6 AM HST Wednesday through Friday afternoon for all Hawaii islands. High Surf Advisory from noon Wednesday to 6 AM HST Thursday for Niihau, Kauai Windward, Kauai Leeward, Oahu South Shore, Waianae Coast, Molokai Leeward, Lanai Makai, Kahoolawe, Maui Leeward West, Maui Central Valley, Leeward Haleakala. High Surf Warning until 6 AM HST Friday for Kona, South Big Island.

Footer

22 Aug 2018 06:51:00 GMT: DISCUSSION...Bohlin/Ballard AVIATION...Hui MARINE...Gibbs

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