West Kaua’i

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Scattered showers. Lows around 70 near the shore to around 60 above 3000 feet. Northeast winds 10 to 20 mph decreasing to up to 20 mph after midnight. Chance of rain 50 percent.

Sunday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 84 near the shore to around 71 above 3000 feet. Northeast winds up to 20 mph. Chance of rain 50 percent.

Sunday Night: Partly cloudy with isolated showers. Lows 67 to 72 near the shore to around 60 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

South Kaua’i

Tonight: Breezy. Mostly cloudy with numerous showers. Lows around 71. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Sunday: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 77 to 85. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Sunday Night: Mostly cloudy with scattered showers. Lows around 71. Northeast winds around 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Breezy. Occasional showers. Lows 62 to 68 in the valleys to around 57 above 4000 feet. Northeast winds up to 20 mph. Chance of rain near 100 percent.

Sunday: Breezy. Occasional showers in the morning, then numerous showers in the afternoon. Highs 69 to 77 in the valleys to around 61 above 4000 feet. Northeast winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain near 100 percent.

Sunday Night: Breezy. Mostly cloudy with numerous showers. Lows 62 to 67 in the valleys to around 57 above 4000 feet. East winds 15 to 20 mph. Chance of rain 70 percent.

North Kaua’i

Tonight: Breezy. Numerous showers in the evening, then occasional showers after midnight. Lows 63 to 72. East winds up to 20 mph. Chance of rain near 100 percent.

Sunday: Mostly cloudy. Breezy. Occasional showers in the morning, then scattered showers in the afternoon. Highs 72 to 84. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 90 percent.

Sunday Night: Mostly cloudy with scattered showers. Lows 63 to 72. East winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Tonight: Occasional showers. Lows 62 to 74. Northeast winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain near 100 percent.

Sunday: Mostly cloudy. Breezy. Occasional showers in the morning, then scattered showers in the afternoon. Highs 69 to 82. Northeast winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 90 percent.

Sunday Night: Breezy. Mostly cloudy with scattered showers. Lows 63 to 75. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A cold front will continue moving down the island chain through Sunday, bringing an increase in showers, especially along windward slopes. Breezy east-northeasterly trades will fill in behind the front and persist through much of next wee, becoming even stronger by mid-week as strong high pressure builds north of the islands. Typical windward and mauka showers will prevail under the trade flow, with generally drier conditions leeward.

Discussion

This afternoon, a weakening cold front is moving down the island chain from northwest to southeast, trailing a strong low pressure system that is moving quickly across the North Pacific with a strong surface high building in its wake. A late morning ASCAT pass placed the front near Kauai, and latest satellite imagery and surface observations suggest it is just north of Oahu this afternoon. A band of clouds and showers along and just ahead of the front is also currently making its way down the island chain, and breezy northeasterly winds are filling in with it's passage. The band of moisture has resulted in increased cloudiness and mostly light showers with occasional brief moderate showers over the western end of the state. Observed rainfall amounts thus far today have been largely around 0.25 inch or less across lower elevations of the Garden Isle, though latest hires guidance and satellite trends suggest that additional light to moderate rain will be possible for Kauai through tonight. Light background winds ahead of the front have resulted in afternoon sea breezes across the remaining islands. Pooled moisture and the front's approach have begun to increase showers across Oahu this afternoon as well.
The front is forecast to progress down the island chain as it weakens, passing over Maui County tonight and reaching the Big Island by early Sunday. Light and variable winds will prevail ahead of the front, shifting to breezy east-northeasterly trades in its wake. Expect an uptick in showers, particularly for windward and mauka areas, as it moves southeast, though the increasing breezy winds may allow some showers to reach leeward areas as well. Mid-level ridging in place over the region will continue to limit vertical development, keeping rainfall rates modest overall. With that said, model guidance is still showing that some windward areas of Maui County and the Big Island could receive a couple of inches of rain from this evening through the rest of the weekend.
Following the front, breezy east-northeasterly trades will become established across the state as high pressure builds to the north. Another reinforcing front with an even stronger high pressure system will arrive midweek, providing another boost in the east-northeasterly trades. With mid level ridging persisting over the region, inversion heights will remain low, keeping the moisture confined to lower levels and focusing clouds and showers over primarily windward and mauka areas.

Aviation

A cold front is pushing through the state with enhanced showers and breezy NE winds. The front has passed Kauai and will continue moving through the island chain tonight, reaching the Big Island tomorrow morning. VFR conditions will prevail ahead of the front, but MVFR conditions are expected during frontal passage. Winds are expected to strengthen out of the NE after the front moves across the state.
AIRMET Sierra is in effect for Kauai windward areas for MTN obscurations due to CLD and SHRA from the front. This is expected to be adjusted as conditions settle behind the front, and other mountainous areas downstream experience CLD and SHRA.
AIRMET Tango is in effect for low-level turbulence over Kauai, and will likely need to be expanded tonight as winds strengthen after frontal passage.

Marine

Rough marine conditions expected through much of the upcoming week due to strong trade winds and a series of north to northeast swells.
A cold front will be making its way through the island chain this evening and tonight and is currently located just north of Oahu this afternoon. As this front pushes through the state, strong northeast winds will follow with a quick rise in seas. Due to the quickly changing conditions behind the front, a Small Craft Advisory was issued for many coastal areas and will likely expand in coverage as the front makes it way through the island chain this weekend. Strong northeast winds are expected through much of the week and could strengthen towards the middle of the week. As the high strengthens and builds north of the area Wednesday into Thursday, we could potentially see gales for some of our typical windy channels around Maui County and the Big Island.
A moderate, short-medium period, north-northwest to north swell will arrive this evening and will produce elevated surf along north facing shores through Sunday. Offshore buoys northwest of the state showed energy mostly in the 10 to 11 second energy bands throughout the day today, which should keep surf under advisory thresholds through at least the first half of tonight for north facing shores. We are expecting a little bit more energy to fill in tonight, which should translate to near borderline advisory level surf along north facing shores for Sunday morning.
A larger moderate period north to north- northeast (010-030 degree) swell will fill in Sunday night into Monday which should exceed advisory thresholds along north and east facing shores. Also due to the northerly direction areas such as west Maui will also see elevated surf as well as some of the exposed areas of west Big Island near Kua Bay. Another reinforcing northeast swell is expected towards the middle of next week as a gale force low develops northeast of the state on Monday. The combination of these swells will likely produce moderate to heavy surges in north facing harbors such as Kahului and Hilo harbors throughout the first half of next week.
A small, long period, south-southwest swell will keep surf heights near seasonal averages along south facing shores today. A pair of south to south-southwest swells should bring above average surf throughout the first half of next week.
Peak monthly tides combined with water levels that are running higher than predicted will lead to minor flooding along the shoreline and in low-lying coastal areas during the morning high tide. A Coastal Flood Statement remains in effect through noon Sunday.

Fire weather

Critical fire weather conditions are not expected through the next few days. Light winds ahead of a frontal passage will transition to become breezy trades through the second half of this weekend, but increasing moisture will prevent critical fire weather concerns. Breezy trades are forecast to become even stronger by mid-week, but low-level moisture embedded within the trades will help keep relative humidity from reaching critical thresholds.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Monday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters.
Small Craft Advisory until 6 PM HST Monday for Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel.

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