Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
733 FXHW60 PHFO 121932 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 932 AM HST Wed Jun 12 2024 .SYNOPSIS... Broad high pressure north of the state will drive moderate to breezy trade winds through the week. Showers will be focused over windward areas, and leeward communities will be rather dry, though the Kona slopes Big Island will experience clouds and showers each afternoon and evening. && .DISCUSSION... A wetter trade wind weather pattern is in place today. Broad surface high pressure located about 900 miles north of Kauai is maintaining moderate to locally breezy trade winds, and a mid- level ridge continues to produce stable conditions, capping low clouds at around 7,000 to 8,000 ft. In contrast to the dry weather to start the work week, there was a noticeable increase in showers overnight, as a shallow area of open celled cumulus clouds with precipitable water in excess of 1.5 inches moved in on the trades. Numerous windward sites picked up over a quarter of an inch of rain during the past 12 hours, and these somewhat wet conditions are expected to continue today. A few of these showers will blow over to leeward areas from west Maui to Kauai, but little rainfall accumulation is expected over these locales. Expect clouds and scattered showers to develop over leeward Haleakala and the Kona slopes of the Big Island this afternoon and linger through the evening. Only subtle changes are due this week. It now looks like the trade winds will remain at moderate to locally breezy strength. We had earlier believed that the surface ridge would weaken as it was displaced southward Friday and Saturday, but recent GFS and ECMWF have trended toward a stronger ridge with no significant changes to local winds. Precipitable water is forecast to lower back to around seasonal average of about 1.25 inches by Thursday, suggesting a slight decrease in showers and typical June conditions. A resilient mid-level ridge will maintain stability, even as an upper-level trough develops over the region this weekend. The ECMWF is hinting that this upper trough may strengthen early next week, but it is too far out to confidently expect any increase in shower activity. && .AVIATION... Moderate to breezy trade winds will persist across the Hawaiian Islands over the next couple of days. Clouds and showers will favor windward and mauka areas, especially overnight, and bring brief periods of MVFR conditions to those areas. Otherwise, VFR conditions should generally prevail. AIRMET Sierra for tempo mountain obscuration is in effect for windward portions of the island chain due to low clouds and showers. These conditions should improve by this afternoon. && .MARINE... Fresh to strong easterly trades will continue through the weekend, as the surface ridge remains north of the area. This supports the Small Craft Advisory continuing for the windier channels and waters around Maui County and the Big Island each day. Surf along south facing shores will slowly ease through Thursday as the current south-southwest swell fades. Expect a mix of this fading south-southwest swell and a small, medium-period southeast swell through Thursday. A fresh, long-period south swell is expected to arrive Thursday night into Friday, then peak late Friday into Saturday. This swell should produce advisory level surf Friday into Saturday then gradually decline Sunday into early next week. Surf along north-facing shores will remain up above the summertime average (flat) through a good portion of the week as small, short-period north to north-northwest swells move through. Surf along east-facing shores will remain small and choppy over the next several days due to limited trade wind fetch upstream of the islands. A slight increase is expected towards the end of the week as the winds upstream of the state strengthens. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Thursday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Wroe AVIATION...Farris MARINE...Kino