West Kaua’i

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy after midnight. Lows 71 to 76 near the shore to around 63 above 3000 feet. East winds up to 10 mph. Chance of rain 40 percent.

Tuesday: Mostly sunny in the morning then becoming partly sunny. Highs 85 to 92 near the shore to around 77 above 3000 feet. East winds up to 15 mph shifting to the southwest in the afternoon.

Tuesday Night: Mostly cloudy in the evening then becoming partly cloudy. Lows 70 to 75 near the shore to around 61 above 3000 feet. East winds up to 10 mph.

South Kaua’i

Tonight: Partly cloudy with isolated showers. Lows around 74. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny. Highs 83 to 91. East winds 10 to 15 mph.

Tuesday Night: Partly cloudy with isolated showers. Lows around 74. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 65 to 71 in the valleys to around 60 above 4000 feet. Light winds becoming east up to 10 mph after midnight. Chance of rain 50 percent.

Tuesday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 76 to 86 in the valleys to around 68 above 4000 feet. East winds up to 10 mph. Chance of rain 40 percent.

Tuesday Night: Mostly cloudy with scattered showers. Lows 64 to 70 in the valleys to around 59 above 4000 feet. East winds up to 10 mph. Chance of rain 40 percent.

North Kaua’i

Tonight: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 67 to 75. Southeast winds up to 10 mph. Chance of rain 30 percent.

Tuesday: Mostly sunny. Isolated showers in the morning. Highs 79 to 88. East winds up to 15 mph. Chance of rain 20 percent.

Tuesday Night: Partly cloudy with isolated showers. Lows 66 to 74. Southeast winds up to 10 mph. Chance of rain 20 percent.

East Kaua’i

Tonight: Partly cloudy with isolated showers. Lows 66 to 78. East winds around 10 mph. Chance of rain 20 percent.

Tuesday: Partly sunny with isolated showers in the morning, then mostly sunny in the afternoon. Highs 75 to 88. East winds around 10 mph. Chance of rain 20 percent.

Tuesday Night: Partly cloudy with isolated showers. Lows 65 to 78. East winds around 10 mph in the evening becoming light. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Showers near Kauai and over the Kona slopes of the Big Island will diminish overnight as light to moderate trade winds bring a drier air mass over the island chain. For the remainder of the week, continued light to moderate trade winds and generally stable conditions will bring modest rainfall to windward areas. While most leeward areas will be rather dry, sea breezes will produce afternoon clouds and a few showers over terrain, especially on the Big Island.

Discussion

An area of moisture within a light to moderate trade wind flow has been producing some active showers over the western end of the island chain this afternoon. Aided by slight instability produced from a nearby upper-level low northwest of the state, a few showers briefly formed along the Waianae Mountains on leeward Oahu around midday, but as drier air pushed westward, this activity has largely moved over interior Kauai and waters just to the south. This moisture has also remained hung up on leeward Big Island and has fueled scattered showers, some briefly heavy, in and around Kailua-Kona. Expect shower activity on Kauai and leeward Big Island to linger into the evening then diminish overnight. Elsewhere, the stable trade wind flow will produce minimal windward rainfall and mostly dry conditions leeward.
A stable and somewhat dry light to moderate trade wind flow will become established on Tuesday. A weak surface ridge parked roughly 300 miles north of Kauai will maintain trades near current strength. The upper-level low will begin to creep northward and allow a strong mid-level ridge, already in place over the eastern half of the island chain, to bring increasingly stable conditions to the entire state. The moisture currently fueling showers around Kauai and over the Kona slopes will move west of the islands, and the incoming drier air mass will produce minimal showers over windward slopes. Most leeward areas will be rather dry, but sea breezes will produce afternoon clouds and a few showers, mainly on the Kona slopes of the Big Island. Little change is expected to the somewhat dry trade wind flow through the coming weekend.
The latest National Hurricane Center forecast has East Pacific Tropical Storm Kiko strengthening into a hurricane before crossing into the Central Pacific Friday or Saturday. It remains too early to tell what, if any, impacts this system might have on the local weather as it nears the islands early next week.

Aviation

Beneath a partial coverage of cirrus aloft, the trade wind inversion has trapped moisture in the 7-9kft layer which will continue supporting SCT-BKN VFR cigs through tonight mainly from Oahu to Kauai. Iso-sct aftn showers over select interior zones will dissipate with the loss of heating this evening followed by moderate trades that will deliver limited showers to windward and mauka zones overnight. Little to no change expected for tomorrow.

Marine

A ridge of high pressure north of the state will remain displaced to the south in response to large low far to the north. This will maintain moderate trades through most of the forecast period, with some localized sea breezes, especially across leeward waters.
Elevated surf will continue along north facing shores due to a short- to medium-period north swell. This swell will quickly be overshadowed by longer-period energy out of the northwest starting tonight. The northwest swell will peak Tuesday afternoon. A reinforcing pulse out of the north should arrive around the same time the northwest swell arrives. A mix of north and northwest swells are expected to continue thereafter, keeping north shore surf elevated, but slowly declining, through Thursday.
Surf along south facing shores will continue to decline through today as the south swell fades, despite a slight boost from short- period southeast energy. Below average surf is expected to continue along east facing shores persisting through early next week.
Peak monthly high tides, combined with water levels running higher than predicted, may lead to minor flooding along the shoreline and in low-lying coastal areas toward the end of next week. Coastal flooding may be possible around the daily afternoon peak tide.

Fire weather

Even as rather dry conditions return tonight and Tuesday, trade winds will remain in the light to moderate range and below the critical threshold this week.

HFO Watches/Warnings/Advisories

None.