Photo Credit: Jason Weingardt

West Kaua’i

Today: Breezy. Partly sunny with scattered showers and slight chance of thunderstorms. Highs 78 to 85 near the shore to around 71 above 3000 feet. Northeast winds up to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Haze in the evening. Scattered showers. Lows 65 to 71 near the shore to around 59 above 3000 feet. Northeast winds up to 15 mph in the evening becoming light. Chance of rain 50 percent.

Friday: Mostly sunny. Isolated showers in the morning, then slight chance of thunderstorms and isolated showers in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 79 to 86 near the shore to around 72 above 3000 feet. Light winds becoming southwest up to 10 mph in the afternoon. Chance of rain 20 percent.

South Kaua’i

Today: Mostly cloudy. Breezy. Numerous showers and slight chance of thunderstorms in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Haze in the afternoon. Highs 76 to 84. Northeast winds 15 to 25 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Breezy. Haze in the evening. Numerous showers in the evening, then scattered showers after midnight. Lows around 69. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Friday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 77 to 85. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Mostly cloudy. Breezy. Occasional showers and slight chance of thunderstorms in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Haze in the afternoon. Highs 68 to 76 in the valleys to around 61 above 4000 feet. Northeast winds 10 to 20 mph shifting to the east up to 20 mph in the afternoon. Chance of rain 90 percent.

Tonight: Haze in the evening. Occasional showers. Lows 59 to 68 in the valleys to around 57 above 4000 feet. East winds up to 10 mph. Chance of rain near 100 percent.

Friday: Partly sunny. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 71 to 78 in the valleys to around 63 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

North Kaua’i

Today: Mostly cloudy. Breezy. Occasional showers and slight chance of thunderstorms in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Haze in the afternoon. Highs 71 to 81. Northeast winds 10 to 20 mph shifting to the east up to 20 mph in the afternoon. Chance of rain 90 percent.

Tonight: Mostly cloudy. Haze in the evening. Occasional showers in the evening, then numerous showers after midnight. Lows 61 to 69. East winds up to 15 mph in the evening becoming light. Chance of rain 90 percent.

Friday: Partly sunny with scattered showers in the morning, then mostly sunny with scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 73 to 82. East winds up to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Cloudy and breezy. Occasional showers and slight chance of thunderstorms in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Haze in the afternoon. Highs 69 to 81. Northeast winds 10 to 20 mph. Chance of rain 90 percent.

Tonight: Haze in the evening. Occasional showers in the evening, then numerous showers after midnight. Lows 62 to 72. Northeast winds up to 15 mph. Chance of rain near 100 percent.

Friday: Partly sunny. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 70 to 82. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A weakening front over the Kauai Channel continues to produce showers mainly impacting Oahu. Lingering moisture combined with an upper disturbance moving over the state will increase rainfall chances statewide today through Friday, along with the chance for thunderstorms. As trade winds gradually return today, the focus of rainfall will shift to windward and mauka areas through early next week.

Discussion

The highest rainfall totals over the past 24 hours range from 1 to 2 inches over Oahu and from .20 to .75 inches over Kauai, as a diminishing stationary front remains between Kauai and Oahu early this morning based on a NE to SW oriented cloud band centered over the Kauai channel. Kauai radar remains down early this morning but the remaining radars and wind observations show showers have increased along windward and mauka areas across the state as winds continue to shift to a more east northeast direction. The morning soundings show the lower levels have moisten up around the Big Island with a dry layer around 9 kft while the Kauai sounding shows upper level temperatures have cooled, as an upper level trough digs south.
Forecast remain on track with the front weakening this morning and shifting westward as a high builds north of the state allowing for moderate to locally strong trades to return tonight into the weekend. The combination of enhanced moisture and increasing upper level instability may be enough to overcome the mid level drying and increase the risk of thunderstorms and locally heavy showers today into Friday. Latest high resolution models still favors the weakening frontal boundary as the area where the most activity will kick off, due to strengthening northeast and east southeast winds along the convergence boundary later this morning and early afternoon. Some elevated stream response is possible, especially for Kauai and Oahu as this boundary shifts from Oahu to Kauai, which may initiate a flood advisory or two. In addition, the Big Island summits may also see periods of wintry precipitation today through Friday.
Friday into early next week, bands of moisture moving with the trades along with lingering upper level instability from the trough cutting off and sagging south of the Big Island will keep enhanced rainfall chances mainly along windward and mauka areas with some showers spilling over to leeward areas at times. Chances for thunderstorms will trend down Friday night into Saturday as deep moisture is pushed west of the state and the upper low moves south of the state.

Aviation

Expect periods with MVFR conditions over the western end of the state persisting today due to a lingering cloud band associated with a diminishing frontal boundary stalled around Oahu. Showers will favor north- through east-facing slopes and coasts in these areas with light to moderate NE to E winds. Heavy showers and a few thunderstorms will be possible today through tonight as an upper disturbance dips south over the state. Another area of moisture moving into the Big Island will continue to support periods with MVFR CIGS/VSBYS.
AIRMET Sierra for mountain obscuration remains in effect for Oahu, Kauai, and the windward slopes of the Big Island.

Marine

Fresh to strong northeast trades will continue around Kauai today, on the northwest side of a weakening stationary front. Meanwhile, moderate to fresh trades will hold over the eastern most waters, and the waters around Oahu and Maui County will remain lighter. The front will have weakened into a trough by late this afternoon, and will begin to shift westward and gradually dampen out through Friday. This will allow for moderate to locally strong trades to fill in from east to west across the island chain. Moderate to locally strong trades should then hold in place through early next week, with only minor fluctuations in strength each day.
A Small Craft Advisory (SCA) is now in effect for all windward waters through 6 am Friday due to winds, seas, or a combination of the two. The SCA has been dropped for many leeward waters as seas have dropped below the 10 foot threshold.
The current extra-large northwest swell has peaked and will gradually decline through Saturday. A High Surf Warning remains in effect for most north and west facing shores through 6 PM this evening. Surf will likely hold at advisory levels for these same areas tonight, before dropping below the advisory threshold for Friday. A new long-period northwest swell will arrive late Saturday and Saturday night, peak Sunday into Sunday night, then lower Sunday night into Monday. This swell will give a boost to surf along north and west facing shores, but will likely remain below advisory levels. The next in the series of northwest swells will arrive early Monday, peak late Monday and Monday night, then gradually decline through the middle of next week. This swell may reach advisory levels as it peaks.
East shore surf not exposed to the series of northwest swells will remain will remain very small today, then gradually rise Friday through Saturday as the trades return over and upstream of the islands. Surf will then hold relatively steady along east facing shores through the middle of next week.
South shore surf will remain very small through the middle of next week.

Fire weather

No critical fire weather conditions are expected today into early next week as enhanced rainfall remains in the forecast.

HFO Watches/Warnings/Advisories

High Surf Warning until 6 PM HST this evening 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, Big Island South.
Small Craft Advisory until 6 AM HST Friday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Alenuihaha Channel, Big Island Windward Waters.

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