Photo Credit: Brendan Stephen

West Kaua’i

Rest Of Today: Partly sunny with numerous showers. Highs around 81 near the shore to around 69 above 3000 feet. Northeast winds around 10 mph shifting to the southwest in the afternoon. Chance of rain 60 percent.

Tonight: Mostly cloudy. Numerous showers early in the evening, then isolated showers in the late evening and overnight. Lows around 67 near the shore to around 56 above 3000 feet. North winds around 10 mph. Chance of rain 60 percent.

Thursday: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 81 near the shore to around 68 above 3000 feet. Northwest winds around 10 mph. Chance of rain 40 percent.

South Kaua’i

Rest Of Today: Partly sunny. Scattered showers in the morning, then numerous showers in the afternoon. Highs around 80. North winds around 10 mph shifting to the south in the afternoon. Chance of rain 60 percent.

Tonight: Mostly cloudy early in the evening then becoming partly cloudy. Numerous showers early in the evening, then isolated showers in the late evening and overnight. Lows around 64. North winds around 10 mph in the evening becoming light. Chance of rain 60 percent.

Thursday: Mostly sunny early in the morning then becoming partly sunny. Isolated showers. Highs around 80. Light winds. Chance of rain 20 percent.

Kaua’i Mountains

Rest Of Today: Mostly cloudy with numerous showers. Highs 73 to 78 in the valleys to around 63 above 4000 feet. Southwest winds around 10 mph shifting to the northeast in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy. Numerous showers early in the evening, then isolated showers in the late evening and overnight. Lows 57 to 64 in the valleys to around 54 above 4000 feet. Northwest winds around 10 mph. Chance of rain 70 percent.

Thursday: Partly sunny. Isolated showers early in the morning, then scattered showers in the late morning and afternoon. Highs 72 to 78 in the valleys to around 63 above 4000 feet. Northwest winds around 10 mph. Chance of rain 50 percent.

North Kaua’i

Rest Of Today: Partly sunny. Scattered showers in the morning, then numerous showers in the afternoon. Highs 72 to 81. South winds around 10 mph shifting to the north in the afternoon. Chance of rain 60 percent.

Tonight: Mostly cloudy with isolated showers. Lows 59 to 67. Northwest winds around 10 mph. Chance of rain 20 percent.

Thursday: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 71 to 80. North winds around 10 mph. Chance of rain 30 percent.

East Kaua’i

Rest Of Today: Partly sunny. Scattered showers in the morning, then numerous showers in the afternoon. Highs 72 to 82. West winds around 10 mph shifting to the east in the afternoon. Chance of rain 60 percent.

Tonight: Mostly cloudy. Numerous showers early in the evening, then isolated showers in the late evening and overnight. Lows 59 to 69. Northwest winds around 10 mph. Chance of rain 60 percent.

Thursday: Partly sunny with isolated showers. Highs 73 to 81. North winds around 10 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Expect light and variable winds and mostly dry weather through tomorrow as moisture lingering over the area gradually dissipates. A fast-moving cold front will bring increased clouds and showers tomorrow night and Friday, especially to north and east facing slopes and coasts. Strong northeast trade winds will follow the front, bringing a significantly cooler air mass, with just a few windward showers through the weekend. Breezy trade winds will continue into next week, with passing clouds and showers favoring windward areas as the air mass gradually warms.

Discussion

A bubble high passing just N of the area has an associated ridge near the islands, where it will remain through tomorrow. Winds have become light and variable, while low-level moisture associated with a dissipated front lingers, mainly in the form of stable low clouds. Satellite shows this E-W oriented, 300 to 400-mile-wide, ragged band of broken to overcast low clouds straddling most of the islands. Radar shows little in the way of rainfall falling from a cloud deck based around 7000', except over portions of windward Big Island, where thicker low clouds dropped anywhere between 1/4″ and 3/4″ of much-needed rain overnight.
The lingering frontal moisture will gradually dissipate today although a new weak frontal cloud band passing to the N may introduce a subtle increase in low-level moisture near Kauai tonight. Land and sea breezes will modulate island weather through tomorrow, with mostly dry conditions prevailing. Afternoon sea breezes will likely drive the formation of some interior and upslope clouds that linger into the evening. Just a few showers are expected as a mid-level ridge S of the area the island atmosphere supports a strong low-level subsidence inversion.
High pressure building NW of the islands late tomorrow and Friday will usher in a cool air mass on strong and gusty NE trade winds. The high will push a relatively weak and fast-moving frontal band over the islands from the N, bringing a period of clouds and showers that will focus over N and E facing slopes and coasts. Initial timing estimates are tomorrow night and Friday for Kauai and Oahu, Friday for Maui County and Friday night for the Big Island, with the moisture axis pushing SE of the Big Island on Saturday. After the frontal passage, limited windward showers are anticipated through the weekend. Dew points lowering into the mid-50's Friday and Saturday will make it feel markedly cooler, especially when compared to the recent low-70's dew points. Max and min temperature forecasts for the weekend were lowered.
Trade winds will persist into the middle of next week as they gradually veer to the E and ESE as the high moves slowly E. The trades will deliver clouds and passing showers that will favor windward and mauka areas, with weak mid-level troughing over the area likely supporting periods of moderate rainfall. Dew points will slowly increase and the weekend chill will gradually ease.

Aviation

A surface trough near the Big Island will continue to focus showers on north and east facing slopes and coasts of Maui and the Big Island early this morning. Periods of MVFR conditions and even IFR conditions are possible in the heavier downpours, with VFR conditions prevailing elsewhere. Drier weather is filtering in from the west, but mid level clouds are also moving in. Light and variable winds will continue through Thursday as a weak surface high/ridge passes overhead. This weaker wind pattern will allow for land and sea breeze development over the next 24 hours.
AIRMET Sierra for mountain obscuration above 1,500 ft is currently in effect for the Big Island early this morning. AIRMET Sierra may also be needed for Maui again this morning for mountain obscuration if low clouds and showers persist.
AIRMET Tango for moderate turbulence below 9,000 ft is in effect for areas north through east of the terrain on Kauai this morning. These conditions should improve by the afternoon.

Marine

Light background winds will persist across the coastal waters through Thursday due to two troughs breaking down the high pressure ridge over the Hawaii region. High seas from a large northwest (310 degree) swell continue to produce Small Craft Advisory (SCA) conditions for exposed western waters through this afternoon. This SCA was extended in time for most western waters and windward Maui waters through this afternoon, and this SCA will likely be cancelled later this evening as wave heights fall below advisory thresholds.
Another cold front will sweep through the islands late Thursday through Friday with moderate to strong north winds filling in behind the front from Thursday night through Friday. A strong high pressure system passing by just north of the island chain will increase northeasterly to easterly trade winds into the strong to gale range across the region. The gale force winds are forecast from Saturday morning through Sunday night affecting all eastern channels including Maalaea Bay and south Big Island waters.
A large medium period northwest swell is slowly declining, however this swell continues to produce advisory level surf along most N and W facing shores of the smaller islands and along west facing shores of the Big Island. Surf heights will decline below HSA levels later this evening for most areas. The HSA remains in effect for most of these exposed north and west facing shores through 6 PM HST this evening. The HSA over west facing shores of the Big Island was extended through Thursday.
As the northwest swell eases through Thursday, guidance shows a mix of a moderate north to north-northeast and west-northwest swell moving through the region. The first northerly swell is from a Hurricane Force low near the Gulf of Alaska with a fetch partially directed towards the Hawaiian Islands. There will be a strong west to east gradient with this next northerly swell with higher swell heights expected near the Big Island and decreasing swell heights over the smaller islands. The north- northeast component will become the dominant swell Thursday night into the weekend. This swell will likely result in advisory level surf for most exposed coasts from Friday into the weekend, with warning level surf for exposed north facing shores of the Big Island possible this weekend. This swell direction may also produce harbor surges and impacts for Hilo Harbor on the Big Island and to a lesser degree Kahului Harbor on Maui. There is still a large degree of uncertainty on precise swell heights and impacts for the eastern half of the state.
Surf along east facing shores will remain small through Thursday due to the lack of trade wind flow. Rapidly building trends are forecast to start along east facing shores from Friday into the weekend as the north-northeast swell builds and strong trades return. South shore surf will remain small through early next week.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST this evening for North and West facing shores of Niihau Kauai Oahu Molokai and for North facing shores of Maui.
High Surf Advisory until 6 PM HST Thursday for West facing shores of the Big Island.
Small Craft Advisory until 6 PM HST this evening for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters.

Data Courtesy of NOAA.gov