Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
912 FXHW60 PHFO 090706 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 906 PM HST Wed May 8 2024 .SYNOPSIS... Trade winds will diminish Thursday through the weekend as a broad surface trough and upper disturbance move in. Added instability associated with these features will lead to an increasing threat for strong thunderstorms and heavy rainfall late Thursday through Saturday. Although the thunderstorm potential will lower Sunday into early next week, plenty of moisture lingering combined afternoon sea breezes and a broad surface trough nearby will support afternoon showers over our interior and leeward areas each day. This potential may continue through the latter half of next week as another upper disturbance approaches. && .DISCUSSION... The evening water vapor imagery showed broad upper troughing over the region with a strong shortwave trough digging southeastward toward the area. The local winds will respond and diminish over the next 24-Hrs as the attendant cold front passes to the north and broad surface troughing evolves over the islands. The short- term guidance has initialized well with this pattern and depicts strong upper height falls late Thursday as the shortwave trough closes off into an upper low as it settles southward into the area Thursday night through Friday. MUCAPES of 1000 to 2000 J/Kg combined with effective deep layer shear values of 35 to 45 knots will support a few strong to severe thunderstorms and locally heavy rainfall that could lead to flash flooding through this period. Impacts could begin over the western end of the state as early as Thursday evening/overnight hours, with a transition to more of a widespread/statewide event Friday through Saturday. Guidance shows the upper low beginning to weaken as it lifts off to the northeast later this weekend, which will support a diminishing threat of thunderstorms. The rainfall chances, however, will likely linger as the aforementioned broad surface trough remains over or nearby to the west Sunday through next week. Expect the light to moderate east to southeast low-level flow to persist, which will allow the land and sea breeze regime to hold for most areas. This combined with a sufficient amount of moisture will keep the rainfall chances up each day, especially through the afternoon and early evening periods with the sea breezes. The wet pattern could persist through the second half of the week as another upper low drops southward into the area drawing up deep tropical moisture over the state. && .AVIATION... Light to moderate trades will persist through Thursday with day time sea breezes and night time land breezes expected over wind- protected leeward areas. Showers will continue to favor windward and mauka areas with an uptick of showers expected later tonight into Thursday morning as a band of moisture approaches from the east. As this moisture band moves in, MVFR conditions will be possible for windward and mountain areas with VFR conditions prevailing across leeward areas through Thursday morning. For tomorrow, sea breeze activity will resume and a disturbance aloft will begin to approach the state, which could enhance shower activity in the afternoon. No AIRMETs are in effect at this time. AIRMET Sierra will be possible late tonight into Thursday morning for windward and mountain areas as a band of moisture moves in. && .MARINE... Moderate to locally fresh trade winds will continue to decline as a strengthen surface trough north of Kauai weakens the local pressure gradient. The trough will strengthen and expand over the islands Thursday night and Friday and linger into the weekend, disrupting the local winds. A strong disturbance aloft moving overhead will bring a threat for strong to severe thunderstorms mainly Friday into Saturday. These thunderstorms will have the potential to produce dangerous wind gusts, hail, and frequent lightning. Moderate east to southeast trade winds will gradually rebuild Sunday or Monday. A long-lived south swell will affect the islands during the next several days. Long-period forerunners have arrived at the nearshore buoys and will continue to build overnight. South shore surf is expected to rise above the summertime average, but will likely peak just below the High Surf Advisory level of 10 feet Thursday afternoon through Friday. We will continue to monitor the buoys overnight in case the swell comes in bigger than anticipated. This long-lived swell will gradually decline Saturday through Tuesday. A series of overlapping long-period south swells will give another sizable boost to south shore surf Wednesday through late next week. The current northwest swell will decrease to tiny levels Thursday and Friday, followed by a small reinforcing short-period north-northwest swell this weekend. A small long period northwest swell will build Sunday night, giving north shore surf a boost early next week. Surf along east facing shores will be well below May average through the middle of next week. && .HFO WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Gibbs AVIATION...Farris MARINE...Jelsema