Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
663 FXHW60 PHFO 221923 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 923 AM HST Sun Sep 22 2024 .SYNOPSIS... Moderate trade winds will prevail through Monday as the surface ridge to the north briefly weakens. Rainfall will favor windward and mauka locations, but a few showers, some heavy, may develop across leeward areas as a disturbance aloft moves overhead. Locally breezy trades and more stable conditions will return on Tuesday and persist into next weekend. && .DISCUSSION... A surface ridge far north of the islands will drive moderate trade winds through tomorrow, and instability produced by an upper- level low will generate briefly heavy showers. The upper-level low is centered just north of Kauai and Oahu this morning and will creep west slowly over the next couple of days. This feature has wiped out the inversion over most of the island chain and is producing high lapse rates above 15,000 ft. However, with no organized areas of moisture expected through Monday, an increase in widespread rainfall is unlikely, and expect the locally scattered showers moving along the trades to be briefly heavy. Localized afternoon sea breezes will generate spotty showers, some heavy, across sheltered leeward terrain, which may produce some minor flooding concerns over leeward Big Island each afternoon. A stronger and more stable trade wind flow will develop on Tuesday. The locally breezy trades will be driven by a tighter pressure gradient between the strengthening low-level ridge to the north and a pair of tropical disturbances passing several hundred miles south of the islands. The upper-level low fill and drift away to the west, and a ridge aloft building in from the east will bring stability. Through the rest of the work week, we will monitor areas of tropical moisture that could clip the Big Island, but expect typical windward rainfall for most islands. && .AVIATION... An upper level low approaches from the north today bringing brief moderate to heavy SHRA mostly occurring along windward and mauka areas, with occasional spillover into leeward areas. MVFR conds can be expected in SHRA but otherwise VFR should prevail. AIRMET Sierra HAS BEEN canceled as conds have improved. AIRMET Tango is in effect for mod turb between FL200 and FL400 over the islands. This AIRMET will be evaluated at next issuance and may be canceled. && .MARINE... Fresh trades ease slightly into Monday as the ridge north of the islands weakens. Locally strong trades then develop Monday night and persist for the remainder of the week. A Small Craft Advisory for the windier waters of Maui County and the Big Island. Surf along north and west facing shores will remain tiny through Monday. A moderate, long-period NW swell will arrive on Tuesday and push surf heights along north and west facing shores well above the seasonal average Tuesday night and Wednesday but will fall short of the High Surf Advisory threshold. Surf along south facing shores will remain just below seasonal average levels as a SW swell advances through area waters. A reinforcing SW swell is expected late Monday into midweek. East shore surf remains small in response to declining trades with an upward trend anticipated beginning Monday night as trades restrengthen. && .HFO WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Wroe AVIATION...Walsh MARINE...JVC