177 FXHW60 PHFO 311314 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 314 AM HST Sat May 31 2025 .SYNOPSIS... Breezy easterly trade winds will persist today, with showers favoring windward and mauka areas. The trades will briefly weaken and shift out of the east-southeast tonight through Sunday as a broad surface trough develops far northwest of the islands. Increasing moisture may lead to enhanced shower activity Sunday into Monday, particularly over the western end of the state. Breezy easterly trades and drier conditions are expected to return during the first half of next week as the trough weakens and shifts away from the region. && .DISCUSSION... A wet and breezy trade wind pattern remains in place this morning, with numerous showers favoring windward and mauka areas. Some of these showers are managing to reach the typically drier leeward areas over the smaller islands, due to a weak mid-level trough, an elevated trade wind inversion positioned between 8,000 and 9,000 ft, and pockets of moisture moving through. Peak overnight rainfall accumulations around the state ranged from a quarter to just under half of an inch (through 2 AM HST). This showery pattern is expected to persist through the morning, gradually improving later in the day as the moisture shifts westward. Upper-level height falls and the development of a broad surface trough far northwest of the state will lead to a weakening and veering of the trades out of the east-southeast late tonight through the second half of the weekend. This evolving pattern will draw increased moisture northward into the area, enhancing instability and supporting greater cloud and shower coverage - particularly over the western end of the state, where the instability will be more pronounced. As winds ease on Sunday, showers will become more focused over interior and leeward areas of Kauai and Oahu during the afternoon, with a few potentially becoming briefly heavy. This unsettled pattern will persist into Sunday night and early Monday, with land breezes developing across the western islands and showers favoring windward and coastal locations - again with the potential for locally heavy downpours. Meanwhile, more stable conditions and a continuation of typical easterly trades are expected to hold across the eastern end of the state. A return to breezy and more stable trade wind conditions is expected by Monday night into the first half of next week as upper-level heights rise and drier air filters in from the east. This will result in a more typical trade wind pattern, with showers favoring windward and mauka areas and generally dry conditions prevailing elsewhere. && .AVIATION... Breezy trades will persist today, then weaken and veer out of the southeast later tonight through Sunday. Low CIGS and SHRA should impact windward and mauka locations, with some spillover to leeward sides. MVFR conditions can be expected in heavier SHRA, with VFR conditions prevailing otherwise. AIRMET Sierra is in effect for mtn obsc for N thru SE sections of all islands. AIRMET Tango is in effect for mod turb of all islands downwind of island terrain. && .MARINE... Fresh to strong easterly trades associated with a surface ridge to the north will continue today, with the strongest winds over the typically windier channels and waters around Maui County and the Big Island. Forecast guidance suggests the ridge will briefly weaken through the latter half of the weekend and as a broad surface trough develops far northwest of the area. This will lead to the trades veering out of the east-southeast to southeast by Sunday, with lighter and more southeast winds over the western end of the state and fresh east-southeast winds continuing over the eastern end. The winds will shift back out of the east and strengthen early next week as the trough weakens and tracks away from the area. Surf along exposed north and west-facing shores will climb well above average for this time of year today as a fresh, medium- period north-northwest (330-340 degrees) swell builds down the island chain. Swell observations at the offshore buoys surged above predicted levels overnight, which will lead to surf heights nearing advisory levels today as it fills in. This north- northwest source will peak today, then steadily lower late tonight through early next week, with heights returning to seasonal levels. Surf along exposed south-facing shores will continue to see a mix of long-period background south-southwest and shorter-period southeast swell through the middle of next week. Another long- period south-southwest swell is possible late next week due to a system passing through our swell window near New Zealand. If this materializes, surf could climb to above average levels by next weekend. Surf along east-facing shores will remain small and choppy through the weekend, then gradually build through the upcoming week due to a return of fresh to strong trades locally and upstream across the northeastern Pacific. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 AM HST Sunday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Gibbs AVIATION...Walsh MARINE...Gibbs