Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
997 FXHW60 PHFO 151939 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 939 AM HST Mon Jul 15 2024 .SYNOPSIS... Breezy trade winds will ease to moderate strengthen Wednesday through Friday as broad high pressure weakens northeast of the state. Stable and somewhat dry conditions will prevail through at least Friday, with light showers favoring windward slopes. && .DISCUSSION... A locally breezy and very stable summertime trade wind flow continues. Broad high pressure driving the trades spreads across the much of the central and eastern Pacific near 35N, though the main high is centered roughly 1,400 miles northwest of Kauai, and ridging aloft continues to produce very stable conditions with an inversion based near 6,000 ft. Precipitable water is running slightly below July average, and the nearby trade wind flow is dominated by a field of shallow stratocumulus. In spite of this, showers were surprisingly active early this morning, with many windward stations measuring between 0.1 to 0.2 of an inch of rainfall during the past 12 hours and a few topping a quarter of an inch. These showers will rapidly diminish midday. Aside from some clouds and a few showers on the South Kona slopes, leeward areas will be mostly dry. No significant changes are expected over the next few days. Trades will ease to moderate strength Tuesday night and Wednesday as a weakness develops within the ridge northeast of the islands. Stable conditions will persist with limited moisture in the trade wind flow. As a result, expect modest windward rainfall, and aside from a few afternoon showers on Kona slopes of the Big Island, leeward areas should be dry. In the long range, trades may strengthen during the weekend, and the GFS and ECMWF suggest that an increase in showers will be possible. && .AVIATION... Breezy to locally windy trade winds will continue through tonight then gradually ease through mid week. Showers and periodic low clouds will favor windward and mauka areas, with a few showers possible over leeward areas overnight. VFR conditions will prevail, with brief MVFR is possible in passing showers. AIRMET Sierra for mountain obscuration may be needed tonight as shower coverage increase. AIRMET Tango for moderate low-level turbulence lee of island terrain is in effect and will continue through tonight due to strong trades. && .MARINE... Surface high pressure to the north-northwest of the islands will remain stationary over the next couple of days and maintain fresh to locally strong trade winds. A Small Craft Advisory (SCA) remains in effect for the typical windier waters around Maui County and the Big Island through Tuesday. As the high pressure drifts northeast, trade winds look to decrease below SCA criteria Wednesday through Friday. The current long period south swell has peaked overnight as the PacIOOS Barbers Point buoy peaked around 5 feet 17 seconds. The spectral density observations from the Barbers Point buoy continues to show long period energy in the 16 to 18 second bands through the morning hours and is expected to maintain surf heights well into High Surf Advisory (HSA) criteria through the day. The HSA for all south facing shores will remain in effect through tonight, then gradually decline through Friday. Rough east shore surf will remain slightly above July average today. The short period wind wave energy will slowly decline as trades upstream of, and eventually over, the islands weaken. East shore surf will fall below average by Wednesday and will decline further through Friday. No significant source of northerly swell is due this week. && .HFO WATCHES/WARNINGS/ADVISORIES... High Surf Advisory until 6 AM HST Tuesday for Niihau-Kauai Leeward-Waianae Coast-Kahoolawe-Maui Leeward West-Kona-Kauai South-East Honolulu-Honolulu Metro-Ewa Plain-Molokai Leeward South-Lanai Leeward-Lanai South-Maui Central Valley South-South Maui/Upcountry-South Haleakala-Big Island South-Big Island Southeast. Small Craft Advisory until 6 PM HST Tuesday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Wroe AVIATION...Ahue MARINE...Shigesato