Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Mostly cloudy. Scattered showers and slight chance of thunderstorms in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Highs around 82 near the shore to around 70 above 3000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy after midnight. Lows 65 to 72 near the shore to around 55 above 3000 feet. East winds up to 15 mph. Chance of rain 30 percent.

Sunday: Mostly sunny. Highs around 82 near the shore to around 70 above 3000 feet. East winds up to 15 mph.

South Kaua’i

Today: Mostly cloudy with numerous showers and slight chance of thunderstorms. Highs around 79. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows 61 to 70. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Sunday: Partly sunny. Breezy. Isolated showers in the morning. Highs around 79. East winds 10 to 20 mph. Chance of rain 20 percent.

Kaua’i Mountains

Today: Frequent showers and slight chance of thunderstorms. Highs 69 to 76 in the valleys to around 60 above 4000 feet. Southeast winds up to 15 mph. Chance of rain near 100 percent.

Tonight: Mostly cloudy with scattered showers. Lows 56 to 65 in the valleys to around 53 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Sunday: Mostly cloudy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 69 to 76 in the valleys to around 60 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

North Kaua’i

Today: Frequent showers and slight chance of thunderstorms in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Highs 72 to 82. Southeast winds up to 15 mph. Chance of rain near 100 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 58 to 68. Southeast winds up to 15 mph. Chance of rain 40 percent.

Sunday: Partly sunny with isolated showers. Highs 72 to 82. East winds up to 15 mph. Chance of rain 20 percent.

East Kaua’i

Today: Breezy. Frequent showers and slight chance of thunderstorms in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Highs 72 to 81. East winds up to 20 mph. Chance of rain near 100 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 56 to 68. East winds 10 to 15 mph decreasing to up to 10 mph after midnight. Chance of rain 40 percent.

Sunday: Mostly cloudy with isolated showers. Highs 72 to 81. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 20 percent.

Detailed Forecast

Synopsis

A band of moisture associated with a trough moving through the islands will keep the chances for showers and thunderstorms up for most windward areas through the morning hours today. Drier conditions with moderate to breezy easterly trade winds will return across the entire state later today through Sunday. Winds will shift out of the southeast and briefly weaken early next week as another upper disturbance and front set up west of the state. Stronger trades are expected Wednesday.

Discussion

Satellite and radar showed a band of clouds with embedded heavy showers developing along a surface trough moving through the islands from east to west. Added instability associated with a weak trough aloft is triggering a few thunderstorms within this band, mostly over the windward areas and waters. Some of this activity could translate to localized flooding concerns this morning where it becomes focused as it moves ashore. Morning upper air soundings confirmed this and depicted modestly steep mid-level lapse rates due to cooler air aloft.
As the trough and residual moisture shift west of the area later today and tonight, expect a drier and more stable pattern to fill in through the second half of the weekend. Easterly trades will return to moderate to breezy levels with high pressure passing to the north, which will keep the best chance for showers over the typical windward and mauka locations overnight through the morning hours. A slight increase in moisture moving through within the trades late Sunday through Sunday night will support better windward shower coverage overnight and into the early Monday morning hours.
Trade winds will shift out of the east to southeast through the day Monday as a deep trough develops several hundred miles west of the state. Instability associated with the trough may enhance cloud cover and shower activity around Kauai and Oahu into Tuesday, with afternoon leeward showers possible. Otherwise, expect showers to favor windward slopes.
Trade winds should strengthen Wednesday as the trough to the west weakens and surface high pressure builds far north of the state.

Aviation

Low clouds associated with a weakening surface trough near Kauai and Oahu will continue to produce brief periods of showers, isolated thunderstorms and localized MVFR conditions this morning in a light wind pattern. Day time sea breezes along the terrain sheltered western slopes will converge with increasing easterly trade winds, building clouds over island mountains and interior sections. Mostly VFR conditions will prevail.
AIRMET Sierra remains in effect for mountain obscuration over Kauai and Oahu due to low clouds and showers.

Marine

A trough near Kauai will gradually weaken and shift west today, allowing trade winds to strengthen to moderate and locally strong levels across the island chain. As a result, a Small Craft Advisory (SCA) has been issued for the typically windy waters around Maui and the Big Island through 6 PM Sunday. Winds may ease and tip east-southeast, particularly over the western islands Monday and Tuesday as a trough develops west of the state. Trades will then fill back in on Wednesday as the trough shifts westward and away from the island chain.
Small surf along the north and west facing shores will hold through the weekend from a pair of small north and northwest swells. A moderate sized long period northwest swell will arrive Monday, peak Tuesday, then gradually lower Wednesday through next weekend. This swell will give a noticeable boost to north and west shore surf late Monday through Wednesday, potentially close to advisory levels on Tuesday.
Near to just below average surf along south facing shores is expected through the weekend from small overlapping south swells. A new long period south swell will build Monday and Tuesday, and peak Wednesday and Thursday near advisory levels. This swell will then gradually lower Friday through next weekend.
Surf along east facing shores will trend up slightly this weekend into early next week as the trades strengthen upstream of the state. East shore surf will build close to seasonal levels by the end of the upcoming work week.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Sunday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov