Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
631 FXHW60 PHFO 311355 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 355 AM HST Sun Aug 31 2025 .SYNOPSIS... Moderate trades will continue through the week, with localized land and sea breezes at times. Mostly dry and stable conditions will prevail, with the exception of a brief uptick in shower activity today through Monday. && .DISCUSSION... High pressure far northeast of Hawaii remains displaced and weakened by a large area of low pressure. This synoptic setup will maintain moderate trades through most of the forecast period, with diurnal sea and land breezes developing across the state, particularly in leeward and interior areas. CIMSS MIMIC Precipitable Water satellite imagery shows a band of tropical moisture moving up the island chain this morning as a weak low tracks westward south of state. As this deeper tropical moisture works its way across the state, it will help to enhance the diurnal convective pattern, with increased shower activity expected along sea breeze convergence zones, particularly over the western slopes of the eastern islands today followed by activity focused mainly over Oahu and Kauai tonight into Monday as moisture begins to exit stage left. Weak cyclonic flow aloft courtesy of a nearly stationary upper level low just northwest of the state will weaken the inversion slightly over Oahu and Kauai giving showers a boost in intensity, particularly over interior and leeward Kauai, but organized heavy rainfall is not anticipated. Mugginess will also be on the rise during this time as dewpoints creep into the low 70s no later than Monday and persisting into Tuesday. Conditions should return to a more typical stable hybrid trade wind and land-sea breeze pattern Tuesday onward, as strong capping builds beneath the mid-level ridge and the surface ridge remains seasonably weak. && .AVIATION... Light to moderate trade winds will prevail through tomorrow, allowing for sea breeze development by this afternoon, bringing clouds and showers to some leeward and interior areas. Deeper moisture moving up the island chain from the southeast to northwest today through tomorrow and some weak instability aloft may allow for these showers to become a little more active during this period, with MVFR conditions focused mainly over windward areas during the overnight and early morning periods and over island interiors and leeward areas each afternoon. VFR should prevail elsewhere. AIRMET Sierra for mountain obscuration is in effect for windward portions of the Big Island this morning. While conditions are expected to improve for this area later today, AIRMET Sierra may be needed for other portions of the island chain as showers develop. && .MARINE... A ridge of high pressure north of the state will gradually shift further south in response to a developing low far north of the state. As the ridge meanders closer to the islands our trade wind speeds will decrease, with gentle to moderate trades expected through early next week. Winds should be light enough for localized sea breezes, especially across leeward waters. Surf along south facing shores is expected to steadily decline through Monday as the swell fades, returning to background levels early in the week. Surf along north facing shores will see a small, short-period swell arriving tomorrow. This swell will be overshadowed by longer period energy out of the northwest starting Monday night, peaking on Tuesday. Another reinforcing pulse out of the north should arrive around the same time the northwest swell arrives. A mix of north and northwest swells are expected Tuesday through Thursday. Below average surf is expected to continue along east facing shores persisting through early next week. Peak monthly high tides, combined with water levels running higher than predicted, may lead to minor flooding along the shoreline and in low-lying coastal areas toward the end of the week. Coastal flooding may be possible around the daily afternoon peak tide. && .FIRE WEATHER... Winds remain on the lighter side as moderate trades prevail through the forecast period. Sea level dewpoints creep into the upper 60s and lower 70s no later than Monday and continue into Tuesday ensuring relative humidity values remain elevated during this time. Drier conditions return mid-week onward. && .HFO WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Farris AVIATION...Farris MARINE...Walsh FIRE WEATHER...Farris