Photo Credit: Brendan Stephen

West Kaua’i

Today: Breezy. Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 84 near the shore to around 70 above 3000 feet. Southeast winds 10 to 20 mph. Chance of rain 90 percent.

Tonight: Cloudy. Occasional showers in the evening, then numerous showers after midnight. Lows around 71 near the shore to around 60 above 3000 feet. East winds up to 15 mph. Chance of rain 80 percent.

Sunday: Cloudy with scattered showers in the morning, then partly sunny with isolated showers in the afternoon. Highs around 87 near the shore to around 72 above 3000 feet. Southeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

South Kaua’i

Today: Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 77 to 84. East winds up to 10 mph. Chance of rain 80 percent.

Tonight: Cloudy with occasional showers. Lows around 70. Northeast winds 10 to 15 mph. Chance of rain 80 percent.

Sunday: Cloudy with numerous showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 78 to 85. East winds up to 15 mph shifting to the southeast in the afternoon. Chance of rain 60 percent.

Kaua’i Mountains

Today: Breezy. Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 71 to 82 in the valleys to around 63 above 4000 feet. South winds up to 20 mph. Chance of rain 90 percent.

Tonight: Cloudy with occasional showers. Lows around 68 in the valleys to around 59 above 4000 feet. Southeast winds up to 15 mph. Chance of rain 90 percent.

Sunday: Cloudy with numerous showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 73 to 83 in the valleys to around 64 above 4000 feet. South winds up to 10 mph. Chance of rain 70 percent.

North Kaua’i

Today: Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 75 to 86. Southeast winds up to 15 mph. Chance of rain 90 percent.

Tonight: Cloudy with occasional showers. Lows 64 to 73. Southeast winds up to 15 mph. Chance of rain 90 percent.

Sunday: Cloudy with numerous showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 77 to 87. Southeast winds up to 15 mph. Chance of rain 70 percent.

East Kaua’i

Today: Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 72 to 82. South winds 10 to 15 mph decreasing to up to 15 mph in the afternoon. Chance of rain 90 percent.

Tonight: Cloudy with occasional showers. Lows 65 to 74. East winds up to 10 mph. Chance of rain 90 percent.

Sunday: Cloudy with numerous showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 73 to 83. Southwest winds up to 15 mph shifting to the south in the afternoon. Chance of rain 70 percent.

Detailed Forecast

Synopsis

A kona low northwest of the state will continue drawing unstable tropical moisture northward over Kauai County through today. The kona low will begin slowly drift north and weaken over the next few days improving trends spreading from east to west, though enhanced rainfall may linger over Kauai and Niihau through tonight. By Monday all islands will see an improvement in weather conditions as easterly trade winds return.

Discussion

A kona low remains centered roughly 850 miles northwest of Kauai with a trough orientated northeast to southwest 150 miles west of Kauai. Radar and satellite imagery shows isolated thunderstorms embedded along the main line of convergence just east of the trough. Radar is now showing this main line of convergence nearing Kauai County from the west early this morning. The Flood Watch for Kauai remains in effect through tonight as current observations remains in line with hi- res model guidance showing rainfall activity picking up this morning. Although most showers will remain light to moderate a few heavy showers and isolated thunderstorms could still develop as the day progress, in addition to this band lingering over Kauai County during the most of the day. A few stray showers could also reach as far as Oahu today so have increased the pops slightly especially for the leeward and interior areas this morning.
A ridge of high pressure will slowly build in from east to west across the state today and Sunday as the kona shifts north and weakens. East southeast winds will keep winds light an variable along sheltered leeward locations down stream of the Big Island. This pattern could also be conducive for showers to develop along the Koolau range this afternoon and evening. Upper levels continue to show divergence aloft that will keep some instability over western end today. Expect more stabilizing trends with decreasing showers as east to southeast winds spread across the state. Likely by Sunday, the moderate to heavy rainfall threat will diminish over Kauai as more stable conditions fill in across the state.
Easterly trade winds will return across the state from Monday onward. Trade showers may be somewhat enhanced during the first half of next week due to lingering moisture and some upper level instability from a short wave trough during the first half of next week. The tongue of high precipitable water vapor should become more normal during the second half of next week allowing for a more typical trade wind pattern.

Aviation

An unstable tropical environment with a low level trough over Kauai will keep MVFR conditions with brief IFR conditions possible in moderate to locally heavy showers through tonight. Lingering instability near Oahu will keep periods of MVFR conditions in showers. Moderate turbulence may develop later this morning over all islands from FL280-400.
Most islands will see light large scale southeast to south winds interacting with overnight land and daytime sea breezes through the weekend. Clouds and showers will build over island mountain and interior sections during the day with some clearing at night for most islands. Kauai will be the exception to this rule as a low level trough will approach the island enhancing clouds and showers through tonight.
AIRMET Sierra in effect for mountain obscurations over all islands.
Occasional light rime icing is expected from Kauai to Oahu in layer 140-FL250.

Marine

Moderate to locally strong east to southeast winds associated with a kona low far north-northwest of the state will persist over the weekend. A shift out of a more typical easterly trade wind direction is expected early next week as it lifts northward and away from the region and the ridge builds to the north. A Small Craft Advisory is now in effect for the windier coastal waters around Maui County and the Big Island through Sunday.
Surf along south facing shores will remain up through early next week due to overlapping, long-period south-southwest swells. The first swell will hold around the advisory level today before briefly lowering Sunday. Offshore buoy observations are holding strong with the peak energy associated with this swell now into the 14-16 second bands. The short-period wind chop added from the southerly winds will linger today, then ease as we transition back to an east to southeast wind regime by early next week. A fresh, long-period south-southwest swell will fill in through the day Sunday, then peak slightly lower than the current swell early next week before easing Tuesday through midweek.
Surf along north facing shores will steadily lower through the weekend, with a return to a more typical pattern for this time of year next week.
Surf along east facing shores will remain well below average through the weekend. An upward trend is possible next week as the trades return locally and far upstream over the eastern Pacific.

HFO Watches/Warnings/Advisories

Flood Watch through late tonight for Niihau, Kauai,
High Surf Advisory until 6 PM HST this evening for Niihau, Kauai Leeward, Waianae Coast, Kahoolawe, Maui Leeward West, Kona, Kauai South, East Honolulu, Honolulu Metro, Ewa Plain, Molokai Southeast, 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 Sunday for Maui County Windward Waters, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters.

Data Courtesy of NOAA.gov