Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
914 FXHW60 PHFO 210652 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 852 PM HST Mon Jul 20 2026 .SYNOPSIS... Light to occasionally breezy trades with an increase in overnight showers. Higher moisture passing through from the east will create thicker overcast and periods of rain mainly over windward exposures and upslope mauka but leeward areas will also experience more precipitation. Recent trade behavior will remain steady through Wednesday with a slight strengthening of winds expected later in the week. Hurricane Fausto will remain far east and away from our offshore waters into next weekend but may still influence localized trade winds going into early next week. && .SHORT TERM UPDATE... Satellite imagery is showing areas of thicker clouds over the upstream nearshore waters, in association with greater easterly moisture advection, traveling toward the islands this evening. Showers are already on the uptick with more organized early evening convection moving across Maui County and Oahu. The quick pace of these cells should keep any localized flooding concerns at bay but they will likely drop a quick few hundredths to tenths of an inch during their passage. This afternoon`s oceanic surface analysis depicts no significant features over or in the vicinity of the islands...just a ridge axis far east of the offshore waters. There will be a noticeable boost in statewide shower activity the next couple of days as batch of higher low-mid layer moisture moves across from the east. Drier air following this moist air mass from late Wednesday onward will ensure a drier late week. && .PREV DISCUSSION... Issued at 333 PM HST Mon Jul 20 2026 Deeper moisture (relative to last night) lurks immediately upstream and will be ushered through the forecast area tonight through Tuesday by persistent moderate trades in the lowest levels. For the most part, a typical distribution of showers focused windward and mauka is expected. However, veering winds within the deepening boundary layer (up to approximately 10kft) yields potential for some leeward convergence downwind of Maui County potentially bringing enhanced shower coverage to Leeward Oahu mainly after midnight tonight continuing into Tuesday morning. As this moisture advances west of the islands mid-week, trades rebound under a broad low amplitude subtropical ridge. Breezy trades, high stability, and limited showers focused windward and mauka then prevail through the weekend. && .AVIATION... Moderate trades will continue through the period. Latest radar and satellite imagery suggests that moisture will circulate towards the islands overnight tonight, making for periodic windward showers and perhaps some spillover showers into leeward sites. The latter sites, however, are generally expected to remain VFR through the period. AIRMET Sierra is in effect for mountain obscuration for windward Maui, Molokai, and the Big Island. This may be expanded overnight as the aforementioned moisture moving in becomes more widespread across the islands. && .MARINE... The trade winds will hold at mostly moderate speeds through Tuesday as a very broad trough has produced a weakness in the subtropical ridge to the northwest of the Hawaiian Islands. Trade winds strengthen to fresh and locally strong speeds Wednesday through Friday as high pressure strengthens north of the island chain. A High Surf Advisory remains in effect for all south-facing shores of the Hawaiian Islands through Tuesday. Latest buoy readings have been showing a gradual downward trend this evening, which may allow surf heights to drop below advisory thresholds earlier than expected. We will continue to monitor the buoys tonight, but the latest readings are showing surf below advisory thresholds by Tuesday morning. The current south southeast swell should slowly fade over the next few days. A powerful low pressure system tracked eastward well south of Tasmania and New Zealand last week. OSCAT pass showed a wide fetch of storm force winds with altimeter passes showing seas above 50 feet. This should translate into very long period forerunners arriving as early as early Wednesday morning and steadily filling in throughout the day Wednesday and peaking on Thursday out of the south southwest. Surf should reach advisory thresholds by Thursday. The very long period energy will make for inconsistent, but powerful waves when they arrive. Several days of advisory level surf is expected starting from Thursday and possibly continuing through Sunday as reinforcing energy arrives over the weekend. Surf along east-facing shores will remain slightly below seasonal levels today through Wednesday as the trades ease upstream of the islands. East shore surf should then build back close to seasonal levels late this week and through the weekend as stronger trades return over and upstream on the islands. Additionally, swell generated by former Tropical Cyclone Elida may give a slight boost to east shore surf during the middle of the week. This weekend, larger surf for east shores generated by Hurricane Fausto is possible and could bring advisory level surf along east-facing shores as well. Surf along north-facing shores will remain at flat to tiny levels through the weekend. && .HFO WATCHES/WARNINGS/ADVISORIES... High Surf Advisory until 6 PM HST Tuesday for Big Island South- Big Island Southeast-East Honolulu-Ewa Plain-Honolulu Metro- Kahoolawe-Kauai South-Kauai Southwest-Kona-Lanai Leeward-Lanai South-Maui Central Valley South-Maui Leeward West-Molokai Leeward South-Niihau-South Haleakala-South Maui/Upcountry- Waianae Coast. && $$ SYNOPSIS/SHORT TERM UPDATE...Blood PREV DISCUSSION...JVC AVIATION...Evans MARINE...Kino