Marine Weather and Tide Forecast for Kaumakani, HI

DISCUSSION
Light winds continue across the state this afternoon as a weak surface trough lingers over the Kauai Channel and high pressure remains far northeast of the islands. Radar and visible satellite imagery show clouds and numerous moderate to locally heavy showers have developed over island interiors this afternoon as sea breezes matured, with several locations receiving over an inch of rain over the last couple of hours. Meanwhile, water vapor satellite imagery shows a deep upper level low just east of the state. This low is helping to enhance the instability across areas east of Kauai. Expect the threat for locally heavy showers and a few thunderstorms to continue through this evening as sea breezes continue. Land breezes should develop shortly after sunset and help to push shower activity to areas near the immediate coast or over the coastal waters tonight.

Wednesday will serve as a transition day where gentle to moderate trades will gradually build back as the surface trough dissipates west of the state. This will allow drier air to slowly filter in from the east. The airmass will also gradually become more stable as the upper level low shifts eastward and opens up to a trough, allowing a mid level ridge to build over the state. Moderate to locally breezy trades are expected to return Friday then hold through early next week as a pair of strong high pressure systems move north of the state. Expect showers to favor windward and mauka areas, particularly during the overnight and early morning hours.

Volcanic emissions and light background east southeast flow will keep vog in place over portions of the state tonight. The returning trades should clear the vog out of the smaller islands by late Wednesday.

AVIATION
A weak trough of low pressure slowly passing over the islands will keep the background wind flow light and variable through tomorrow afternoon. This flow pattern will lead to land breezes in the morning hours and sea breezes in the afternoon and early evening hours. Diurnal heating, combined with instability aloft, will combine to generate locally heavy showers in the afternoon and evening hours. Slight chance of thunderstorms over inland areas tonight. Brief periods of MVFR/IFR conditions may occur with the more robust showers and storms.

AIRMET Sierra for mountain obscuration is currently in effect for Oahu, Molokai, Maui, Lanai, and northern Big Island. Conditions are expected to improve later this evening as winds shift from onshore to offshore.

SIGMET November for thunderstorm activity just northeast of the Islands has been canceled. The potential for thunderstorm redevelopment along the major flight routes between Hawaii and California will remain through late this evening.

MARINE
A trough of low pressure near Kauai will linger through the night and continue to weaken the high pressure ridge over the Hawaiian Islands, maintaining light and variable winds across the region.
This boundary combined with an upper level disturbance moving down the island chain will keep the potential for showers and thunderstorms over the coastal waters. Trades will build back in from tomorrow onward, strengthening to Small Craft Advisory levels for the typical windier coastal waters around Maui and the Big Island by Thursday.

A small northwest swell will continue to slowly fade into tomorrow morning, allowing surf along north and west facing shores to remain near or below average levels for this time of year (6 feet for the month of May). By Thursday, a moderate long period north- northwest swell is expected to arrive, producing surf above the seasonal average. This north-northwest swell will slowly decline over the weekend.

Multiple small south swells will maintain small background southerly energy today. A bump up in south-southwest swell energy will arrive tomorrow, peak Thursday producing moderate surf, and then slowly fade through the weekend. However, a mix of reinforcing south- southwest swell and new south-southeast swell energy will arrive this weekend and should help maintain surf near or above the summer average (5 feet). Then another pulse of south-southwest swell energy will arrive early next week.

Weak upstream trade wind flow will keep surf on the small side for east facing shores. An increase is expected by tomorrow as the trade winds return. Trade winds should strengthen through Friday with rough and choppy surf expected along east facing shores through the weekend.

HFO WATCHES/WARNINGS/ADVISORIES
None.