Marine Weather and Tide Forecast for Maunaloa, HI

DISCUSSION

An upper level low continues to build over the state this evening generating significant amount of instability. A surface trough located just west of Kauai is generating light to moderate east to southeast flow over the state with precipitable water values around 1.5 inches.
Infrared satellite imagery and radar show mostly cloudy conditions in place with numerous showers and isolated thunderstorms mostly along windward Maui and Oahu with a few showers developing over leeward Big Island and Kauai. Main short term focus revolves around the potential for heavy rain and thunderstorms during the next couple days.

The surface troughing will hold in place into Friday, continuing light to moderate east southeast winds allowing for nighttime land and daytime sea breezes. As the upper low slowly moves eastward tonight into Friday, 500 mb temperatures of -12 to -13 C and precipitable water values around 1.5 to 1.6 inches will continue the threat of heavy showers and isolated thunderstorms across any of the islands. Land breezes may help suppress the heavy rain over the islands by late tonight into Friday morning, but the focus will shift back over the islands by midday Friday. Snow is expected across the high elevation summits of the Big Island and Winter Weather Advisory remains in effect through 6 PM Friday for elevations above 11,000 feet.

The upper low will open up to a trough and weaken through the weekend. Thunderstorms or heavy showers could be possible after Friday given the remnant moisture around the islands, but the atmosphere over Hawaii will begin to stabilize and will lower the chances for this. Precipitable water values continue to hold close to 1.5 inches through the weekend and the latest model trends have been for weak trade winds. As a result, the pattern looks a bit showery through the weekend, with both windward showers, and chances for showers each afternoon and evening in leeward areas as well. A new, potent storm system will bring southerly winds beginning Monday and another round of potentially significant rainfall Tuesday through Thursday.



AVIATION
Unstable east-southeast winds will maintain widespread MVFR conditions across most east and southeast slopes with pockets of heavy showers and thunderstorms producing IFR conditions tonight.
A surface trough west of Kauai will creep away from the islands on Friday, though will gentle to moderate winds persist out of the east to southeast. An upper-level low, currently centered near Oahu, will drift eastward, maintaining instability statewide tonight, and the greatest chances for heavy showers and thunderstorms shifting to the eastern half of the island chain Friday.

Airmet Sierra is in effect for mountain obscuration over east and south facing areas of Kauai, Oahu, and Maui due to reduced visibility and low ceilings in heavy showers and thunderstorms.

Moderate upper-level turbulence will be possible near and west of the upper low center. AIRMET Tango remains in effect for Kauai and Oahu through midnight and will shift eastward and diminish on Friday.



MARINE
Light to moderate east-southeast winds will persist into Friday due to a broad surface trough located west of Kauai. Over the western end of the islands, the light winds will allow a land and sea breeze pattern to continue near the coasts. For the eastern end, light to moderate east to southeast breezes, with localized fresh pockets, will likely persist, particularly around the Big Island. Expect spotty heavy showers and thunderstorms to continue into Friday due to an upper disturbance in the area.

A return to moderate easterly trades is possible by the weekend as high pressure builds to the north. Heavy showers and thunderstorms will remain possible into Friday due to an upper disturbance in the area. Guidance continues to show the trades becoming disrupted and shifting out of the south early next week as deep low pressure sets up nearby to the west

Surf along exposed north and west facing shores is quickly rising this evening as a fresh north-northwest builds down the island chain. Observations at the offshore buoys to the northwest peaked above the predicted levels this afternoon, which will correspond to the surf peaking overnight and into Friday morning. Heights could briefly near warning levels during this peak (around midnight). A downward trend is then expected over the weekend, with the swell shifting out of north.

Surf along east facing shores will remain below the April average through at least Saturday, then steadily rise to around average by early next week.

Surf along south facing shores will remain small, with mainly overlapping background south swells moving through. A larger pulse of south-southwest swell may arrive Tuesday.



HFO WATCHES/WARNINGS/ADVISORIES
High Surf Advisory until 6 AM HST Friday for Waianae Coast-Oahu North Shore-Maui Windward West-Kauai North-Molokai Windward- Molokai North-Molokai West-Maui Central Valley North-Windward Haleakala.

Winter Weather Advisory until 6 PM HST Friday for Big Island Summits.