Heavy showers and thunderstorms will remain possible across most of the state through at least tonight, while easterly trade winds that remain in place across Big Island and Maui spread to Oahu and Kauai. The upper level disturbance creating the active weather will slowly move eastward and weaken on Saturday, leading to decreased chances for heavy rainfall across most islands. Somewhat wet easterly trade winds will focus most rainfall along windward slopes Sunday into early next week. A more stable, moderate to breezy trade wind flow is expected by Wednesday.
Heavy showers and thunderstorms diminished sharply late this afternoon and evening over and around Oahu. The upper level low that dropped over the state earlier today is now weakening, and the surface trough that it induced over Oahu has filled and lifted to the northwest. This resulted in the dramatic decrease in convection on Oahu as easterly trade winds filled back in, but not before many stations on Oahu measured between 4 and 7 inches of rain, leading to flash flooding. That said, the weakening upper level low will linger overhead and maintain some threat of additional flooding tonight from Oahu to Big Island.
Chances of heavy showers and thunderstorms will diminish from west to east on Saturday as the upper low drifts eastward and weakens. Moderate easterly trade winds will focus rainfall over windward areas, and the GFS and ECMWF are showing increased moisture moving over the Big Island and possibly Maui, suggesting more rainfall across those windward and southeast slopes. Given the lingering instability from the upper level low, heavy rainfall may remain a threat on the Big Island and perhaps Maui, and we will determine if the Flood Watch needs to remain in effect for those islands.
Moderate easterly winds and a somewhat wet pattern of mainly windward and mauka showers is expected by Sunday. The upper low will be replaced by a broad and flat upper trough, which will not allow the atmosphere to become very stable. As a result, we cannot rule out a briefly heavy shower, mainly over the heated leeward slopes of the Big Island and Maui during the afternoon hours.
Increased stability and stronger trade winds are due late Tuesday or Wednesday. Expect a typical pattern of mainly windward rainfall and mostly dry conditions leeward.
An upper level low moving over Maui County this evening will keep unsettled easterly wet trade winds in the forecast with periods of MVFR conditions across the eastern half of the state lasting into Saturday. Shower activity will decrease from west to east this weekend as the upper low weakens and continues to March eastward.
AIRMET Sierra remains in effect for mountain obscuration over Kauai, Oahu, Molokai, Lanai and Maui.
Winds will remain slightly east southeasterly this weekend at moderate to fresh levels. By Saturday, the upper disturbance that gave us some severe weather today will be moving northeast away from the state, with stability slowly returning to the region. As a result, expect decreasing heavy showers and thunderstorms across the waters. A more typical easterly trade wind pattern will return next week.
A small, medium period north northwest (320-330 degree) swell that peaked last night will continue to slowly decline tonight. Surf along north and west facing shores will follow suit, easing during the weekend.
A mix of small, medium to long period south swells will maintain small surf along south-facing shores this weekend. A series of gale lows passing south of New Zealand should send small south swell energy into the southern waters through next week. Surf should lift to summer averages around Sunday and hold through Wednesday. Moderate to fresh trades will maintain rough and choppy surf along east-facing shores.
Tides will peak around 2.5 to 3.0 ft MLLW this weekend. Minor overwash of low lying coastal areas will be possible during times of high tide.
Flood Watch until 6 AM HST Saturday for Waianae Coast-Oahu North Shore-Olomana-Central Oahu-Waianae Mountains-Lanai Mauka- Kahoolawe-Maui Windward West-Maui Leeward West-Haleakala Summit- Kona-Kohala-Big Island Interior-Big Island Summits-East Honolulu- Honolulu Metro-Ewa Plain-Koolau Windward-Koolau Leeward-Molokai- Lanai Windward-Lanai Leeward-Lanai South-Maui Central Valley North-Maui Central Valley South-Windward Haleakala-Kipahulu- South Maui/Upcountry-South Haleakala-Big Island South-Big Island Southeast-Big Island East-Big Island North.
