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Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
309 FXHW60 PHFO 150621 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 821 PM HST Sun Jul 14 2024 .SYNOPSIS... High pressure north of the Hawaiian Islands will hold through early Monday, maintaining a dry trade wind pattern. Light windward and mauka showers will primarily occur during overnight through early morning hours each day. A mid to upper level disturbance developing northeast of the state this week will weaken trades from Tuesday onward. && .DISCUSSION... Updated the forecast this evening to reflect drier conditions through Monday night for the smaller islands. This is largely based on the lack of rainfall over the last day or so. Many of the models, both high resolution and global, show higher PoPs than what we have been experiencing. The updated forecast leans heavily on the HRRR model. Otherwise, the forecast philosophy remains the same. A broad high pressure system remain about 800 miles north of the state, continuing to funnel moderate to locally breezy trades to the region. An upper level ridge over the islands is helping to maintain a dry and stable airmass over head, thus the update mentioned above to dry out the forecast. Satellite continues to show stable stratocumulus clouds riding in on the trades. Expect this pattern to hold through Monday night. A trough developing into a front to the far northeast of the islands will help to disrupt the broad ridge to the north Monday and Tuesday. Around the same time, an upper level trough develops to the northeast, with a possible mid to upper level low developing midweek. These features will help to weaken the trade wind flow over the islands Tuesday onwards. The mid to upper level low looks to remain well enough east of the area that the upper level ridge remains anchored over the islands. This should continue the stable and mostly dry airmass through the week. Towards the end of the week, the upper level trough may approach the islands, which could provide a little more instability leading to a modest increase in showers, particularly over the eastern end of the state which would be closest to the upper level trough. && .AVIATION... Breezy to locally windy trades will continue through Monday before easing slightly into mid week. Mainly light showers and periodic low ceilings will favor windward and mauka locations with a few showers making it to leeward locations. Some brief MVFR conditions are possible in passing showers, otherwise VFR conditions will prevail. AIRMET Sierra may be needed with low ceilings and a slight increase in showers expected tonight into the morning hours on Monday. AIRMET Tango for moderate low-level turbulence lee of terrain is in effect and will likely be needed through Monday due to the strong trades under a strong inversion. && .MARINE... Surface high pressure north of the islands between 30N and 40N will maintain fresh to locally strong trade winds the next couple of days. A Small Craft Advisory (SCA) remains in effect for the typically windier waters surrounding Big Island and Maui County through Tuesday afternoon. Trades will drop off to more moderate speeds, or fall below SCA criteria, Wednesday through Friday in response to lower pressure northeast of the state. Offshore NOAA buoy data from the past several days (i.e., the PacIOOS Aunuu buoy off of American Samoa) has timed the island`s latest south swell moving around the chain through Monday... peaking tonight through Monday morning. This swell will produce frequent sets that exceed the 10 foot High Surf Advisory (HSA) thresholds for southern shores. Nearshore southern buoys are displaying a 4 foot, 16 to 18 second period rising swell with web cams confirming HSA level surf this evening. The HSA currently runs through Monday afternoon, but it may need to be extended through Monday night if the swell holds larger than anticipated. South shore surf will fall below the advisory levels by Tuesday, then gradually decline through Friday. Rough east-facing shore surf will remain slightly above July averages into Monday. This short period wind wave energy will slowly decline as mid week trades upstream of, and eventually over, the islands weaken. East surf will fall below seasonal averages Wednesday and will fade further into Friday. No significant source for northerly swell is expected for the remainder of the week. && .HFO WATCHES/WARNINGS/ADVISORIES... High Surf Advisory until 6 PM HST Monday 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...M Ballard AVIATION...Farris MARINE...Blood