Forecast Discussion

Synopsis

22 Dec 2024 19:29:00 GMT: Breezy trades return for the first half of the week bringing a modest increase in showers windward and mauka. Light winds then give way to a land and sea breeze pattern with afternoon clouds and isolated showers over island interiors during the second half of the week.

Discussion

22 Dec 2024 19:29:00 GMT: The trade wind belt remains weakened and suppressed south of the islands leaving the forecast area in the zone of light winds and subsidence equatorward of an extended Pacific jet. A kink in the mid-latitude flow well northwest of the forecast area will evolve into a progressive mid-latitude ridge that will amplify as it transits the Pacific during the next several days leading to surface pressure rises over and north of the Hawaiian Islands. This will in turn allow trades to rebound back into the area late tonight into Monday and continuing into Tuesday. A few additional showers can be expected windward and mauka during this time, but high stability and a dry airmass will significantly limit shower coverage and intensity. High pressure then continues its eastward trek thereby returning the islands to a weakened trade wind state for the second half of the week. Winds then veer to the SE in response to a weakening front approaching from the northwest. This will favor a return to a land and sea breeze pattern over the western half of the state. Dry and benign weather prevails for the forseeable future.

Aviation

22 Dec 2024 19:29:00 GMT: A strong surface ridge over the Hawaiian Islands will maintain light winds today allowing for the development of afternoon sea breezes. This will result in clouds and a few showers inland. VFR will prevail, but brief MVFR is possible with passing showers. Trade winds return late tonight with clouds and showers favoring windward and mauka areas. No AIRMETs in effect.

Marine

22 Dec 2024 19:29:00 GMT: Hazardous marine conditions will persist into Monday, with the largest in a series of extra-large, overlapping northwest swells today. Observations at the offshore buoys northwest of Kauai show a 20-21 foot swell appearing to have leveled off this morning with the peak of this swell expected to reach the islands this afternoon, then gradually ease late tonight through Tuesday. Resulting surf should reach giant levels, in excess of 40 feet (faces) along coastlines with the highest exposure. Heights could hover at or above warning levels well into Monday before lowering to advisory levels by Tuesday. This extended period of warning-level surf, which began last Wednesday, will produce significant coastal impacts, including considerable beach erosion along exposed shorelines and potential overwash onto vulnerable coastal roadways and properties, particularly during the peak today. These impacts will remain likely despite monthly tidal minima, underscoring the magnitude of this swell. Mariners should also anticipate hazardous conditions, including strong currents and occasional breaking waves near harbor entrances, making transits potentially dangerous. Winds across coastal waters will remain light and variable today as a surface ridge lingers over the region. However, a fast- moving surface high approaching from the northwest will lead to a rapid increase in northeast winds tonight, followed by fresh to strong trade winds as the high passes north of the state on Monday. A Small Craft Advisory (SCA) remains in effect for seas exceeding 10 feet, and as winds increase, the SCA will be expanded to include wind-affected zones. Trades are expected to gradually decline and shift southeasterly on Tuesday and Wednesday as the high moves eastward.

Fire weather

22 Dec 2024 19:29:00 GMT: Minimal fire weather concerns at this time to relatively light winds and elevated RH.

HFO Watches/Warnings/Advisories

22 Dec 2024 19:29:00 GMT: High Surf Warning until 6 AM HST Monday for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Maui Windward West, Kona, Kohala, Kauai North, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala. High Surf Advisory until 6 AM HST Monday for Big Island East, Big Island North. Small Craft Advisory until 6 AM HST Monday for all Hawaiian waters except Maalaea Bay,