Marine Weather and Tide Forecast for Koloa, HI

DISCUSSION
Showers were numerous this afternoon across the Kona region on Big Island and across Oahu, and isolated to scattered on other islands. Between low clouds associated with the showers, and high clouds streaming northeast, skies were mostly cloudy early this afternoon. Trade winds were building in across the region, with northeast winds averaging 10 to 20 mph with gusts 20 to 30 mph in most areas.

Over the next few days, a weak broad trough aloft to our north will be replaced with a ridge. This change aloft will help create a stronger surface ridge to the north, and this will strengthen our developing trade winds. A weak surface trough, associated with an increase in moisture, was moving west through the central islands this afternoon. It is expected to continue slowly moving west as it weakens further, exiting the state by Monday. As it does, expect areas of showers to continue to develop and be carried west or WSW on the developing trade winds.

These trades will strengthen through Sunday, and remain moderate to breezy through most of the coming week. Upper ridging to our north will be the dominant feature of the coming week. However, models are coming into better agreement that an upper low may interrupt the ridge beginning around the middle of next week. There is little agreement on how strong this low might be or exactly where it will be positioned. The general consensus at this time is for it to form sometime between Wednesday and Friday, most likely to our northeast. It could end up being a factor in our weather (increased chance of rain and/or weakening trades), but it is too early to be sure. Otherwise, expect a typical trade wind pattern beginning Monday, with showers mainly windward and mauka.

AVIATION
Moderate trades this afternoon will weaken some tonight, then steadily increase throughout the day Sunday becoming locally breezy by the afternoon. A weak trough currently passing through the state will increase showers, especially over windward and mountain areas with periods of MVFR conditions expected throughout the rest of the afternoon. A drier airmass will move in from the east this evening, which should bring a decrease of showers tonight from east to west. One exception is over Kauai, where showery conditions are expected to persist through tonight. Sunday should be a much drier day with some lingering moisture near Kauai.

AIRMET Sierra remains in effect for mountain obscuration over Kauai, Oahu, Molokai and Maui due to the passing showers. AIRMET Sierra should get cancelled from east to west tonight as the drier air moves in.

There will likely be a need for AIRMET Tango for low-level turbulence as trades gradually strengthen Sunday afternoon into the evening.

MARINE
A ridge will remain in place north of the islands with fresh trade winds tonight, strengthening Sunday and Sunday night and maintaining next week. A Small Craft Advisory (SCA) is posted for waters around Kauai and windward Oahu, and waters around Maui County and Big Island through tonight.

A small northwest swell will maintain through the rest of the weekend, shifting out of the north to north northwest next week.
Small south swell will fade this weekend with a small, long period reinforcement Monday through Thursday. Surf along east facing shores will remain below normal this weekend, but will gradually increase next week as trade winds strengthen.

HFO WATCHES/WARNINGS/ADVISORIES
Small Craft Advisory until 6 AM HST Sunday for Kauai Channel- Kauai Leeward Waters-Kauai Northwest Waters-Kauai Windward Waters-Oahu Windward Waters.

Small Craft Advisory until 6 AM HST Monday for Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters- Maalaea Bay-Pailolo Channel.