textproduct: Honolulu

SYNOPSIS

Breezy trades will gradually weaken through the weekend as a stout low pressure system developing to the far north disrupts the surface ridge extending over the islands. Clouds and showers will favor windward and mauka areas through Friday, then focus shifts to sea breezes each afternoon over the weekend. Early next week, increasing moisture will move up the island chain from the southeast, increasing rain chances for the eastern end of the state Monday and Tuesday. Moderate to locally breezy trades are expected to return shortly thereafter for the remainder of the forecast period.

DISCUSSION

A strong surface ridge positioned north of the state will remain the primary driver of weather conditions across the Hawaiian Islands today. This pattern will continue to support moderate to locally breezy trades and maintains periodic shower activity mainly focused over windward and mauka areas. In addition, a weak upper-level trough quickly moving west to east across the state this morning will temporarily weaken the low-level inversion, allowing for a slight increase in moisture, cloud cover, and shower activity through the morning hours.

Trades will begin to weaken shortly thereafter as a broad area of low pressure develops southward from the Aleutian Islands. This system will erode the surface ridge and weaken the local pressure gradient, leading to lighter winds and the potential for localized land and sea breeze development through the weekend and into early next week. As a result, interior and leeward areas may experience increased afternoon cloud and shower development, followed by overnight clearing.

Model guidance indicate that moisture levels will gradually increase between Monday night and Wednesday as a large plume of tropical moisture lifts northwestward across the island chain from the southeast. Meanwhile, ridging will begin to rebuild over the region as the low pressure system lifts northward into the Gulf of Alaska, allowing trades to strengthen once again. This return to a more typical trade pattern will favor isolated to locally scattered showers, mainly favoring windward and mauka areas, through the remainder of the forecast period.

AVIATION

Moderate to breezy trades through today then decreasing this weekend. Low cigs and SHRA along windward and mauka locations. MVFR conds possible in SHRA otherwise VFR prevails.

AIRMET Sierra is in effect for mtn obsc for Kauai, Oahu and windward Big Island. Conds should improve later this morning.

AIRMET Tango is in effect for mod turb across all islands downwind of terrain.

MARINE

Fresh to strong trade winds will persist today as the subtropical ridge remains strong north of the state. This will support an extension of the Small Craft Advisory through this afternoon for the windier waters around Maui and the Big Island. Thereafter, guidance depicts the ridge beginning to weaken in response to broad low pressure developing roughly 1,500 nautical miles to the north near the Aleutian Islands this weekend through early next week. This will translate to local trades easing into the light to moderate range, likely giving way to localized land and sea breezes near the coasts late this weekend through early next week. A return of moderate to fresh easterly trades is likely by midweek as the ridge strengthens.

An active pattern is in store for surf along south-facing shores as we head into June due to a series of recent gale- to storm- force lows passing through our swell window near New Zealand over the past week. Expect surf to gradually build today as forerunners from a long-period south-southwest swell arrive while the current medium-period south swell fades out. Our buoys are already reflecting this new source with energy registering in the 20-23 second bands this morning. Surf heights will likely reach the advisory level by tonight, with the swell becoming fully established by Saturday. Heights will hover near the advisory level through the weekend. As the swell gradually begins to ease early next week, long-period forerunners from the next south- southwest swell are expected to arrive. Heights may briefly dip below the advisory level Monday night, but as the next swell fills in, surf will likely return to the advisory level Tuesday through midweek as it peaks. A gradual downward trend is then expected through the second half of next week.

A combination of advisory-level surf this weekend and water levels hovering above predicted levels could lead to some wave runup issues, with water sweeping across areas of beaches that typically remain dry. Water levels will steadily lower each day early next week as the next large south swell arrives.

The current small northwest swell will slowly lower through Saturday before fading on Sunday. A small north swell will likely produce surf near seasonal averages along north-facing shores from late Tuesday or Wednesday into Thursday.

Expect surf along east-facing shores to remain near seasonal averages today, then gradually decline through early next week as trade winds ease. A slight increase is possible Tuesday and Wednesday due to a combination of rebuilding trade winds and a wrapping north swell.

HFO WATCHES/WARNINGS/ADVISORIES

Small Craft Advisory until 6 PM HST this evening for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters.