Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
943 FXHW60 PHFO 220149 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 349 PM HST Mon Jul 21 2025 .SYNOPSIS... Moderate to locally breezy trade wind will prevail through much of the week as periods of thin high clouds continue to pass overhead. On most days, showers will favor windward areas, and aside from scattered afternoon showers on the South Kona slopes of the Big Island, leeward areas will be mostly dry. On Wednesday, winds will decline and shift more easterly, leading to more widespread leeward sea breezes and bringing higher chances for interior and leeward showers on mainly Kauai. && .DISCUSSION... A moderate to locally breezy and rather stable trade wind flow is in place. Broad surface high pressure far north of the state is driving the trades. A ridge aloft centered just south of the state is gradually building overhead, bringing increasingly stable conditions, and an upper-level trough sitting roughly 900 miles to the northwest of the islands is sending thin high clouds over the area. Under these locally breezy and stable conditions, windward rainfall decreased considerably, though Kauai remained slightly wetter until midday, and afternoon soundings showed a low-level returning at just over 6,000 feet. Little change is expected through Tuesday. Locally breezy and rather stable trade winds will focus modest showers over windward areas, and with the exception of scattered afternoon showers over the South Kona slopes, leeward areas should be mostly dry. The pattern aloft will remain relatively unchanged, and patches of high clouds will continue to stream overhead. Subtle changes are in store for Wednesday. The upper-level trough and its associated surface trough to the northwest of the state will strengthen, and a shortwave aloft will pass near Kauai. Winds across the western half of the island chain will veer easterly or possibly even out of the east-southeast as the inversion erodes. As a result, afternoon sea breezes could become more extensive and drive higher chances for leeward showers. Since there does not appear to be an influx of increased moisture, heavy showers appear unlikely at this time. A return to stable summertime trade wind conditions is due on Thursday as the surface and upper-level trough to the northwest weaken. Expect moderate easterly trade winds to bring typical showers to windward areas. && .AVIATION... Moderate to locally breezy trades will persist over the next couple of days with clouds and showers favoring windward and mountain areas, particularly during the overnight and early morning hours. Brief periods of MVFR conditions will be possible as these clouds and showers roll in. Otherwise, VFR conditions are expected to prevail. No AIRMETs are currently in effect. If shower coverage becomes widespread enough overnight, AIRMET Sierra for tempo mountain obscuration may be needed for some windward areas. && .MARINE... Moderate to fresh easterly trade winds will continue through Thursday as surface high pressure remains centered far north of the Hawaiian Islands. A Small Craft Advisory remains in effect for the waters around Maui County and the windier waters around the Big Island. Lighter winds are then expected Thursday night into the weekend as the high drifts northwest and a new high develops northeast of the region. Several pulses of southerly and southwesterly swells will continue to boost surf heights along south and some west facing shores this week. Surf along east facing shores will remain small and choppy. Surf along north facing shores will remain nearly flat through the forecast period. Peak monthly high tides associated with the lunar cycle, combined with water levels that are running higher than predicted may lead to minor flooding along the shoreline and in low-lying coastal areas. Coastal flooding is expected around the daily peak tide each afternoon through Thursday. A Coastal Flood Statement has been issued for Maui County and the Big Island where observed water levels are currently around 0.25 to 0.50 feet above the forecasted tides. && .FIRE WEATHER... Locally breezy, dry, and stable conditions returned this afternoon, and with winds blowing stronger than expected within a slot of dry air passing over the islands, weather observations at the Honolulu International Airport (HNL) have been hovering right around critical levels. Winds at other leeward sites are not as strong, and we will hold off on any headlines at this time. KBDI at HNL has exceeded 600 and will remain elevated above that threshold until significant rain occurs, which is unlikely for weeks or possibly months as the peak of the dry season is near. Expect similarly dry and stable conditions on Tuesday, with near critical winds and relative humidity. East to east southeast winds on Wednesday will likely be lighter over sheltered leeward areas. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Tuesday for Kaiwi Channel- Maui County Windward Waters-Maui County Leeward Waters-Maalaea Bay-Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters- Big Island Southeast Waters. && $$ DISCUSSION...Wroe AVIATION...Farris MARINE...Ahue FIRE WEATHER...Wroe