Photo Credit: Jason Weingardt

West Kaua’i

Today: Breezy. Mostly sunny with isolated showers. Highs 83 to 88 near the shore to around 73 above 3000 feet. East winds 15 to 25 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Breezy. Isolated showers after midnight. Lows 68 to 74 near the shore to around 60 above 3000 feet. East winds 15 to 25 mph. Chance of rain 20 percent.

Friday: Breezy. Sunny with isolated showers. Highs 82 to 87 near the shore to around 72 above 3000 feet. East winds 15 to 25 mph. Chance of rain 20 percent.

South Kaua’i

Today: Windy. Partly sunny with scattered showers early in the morning, then mostly sunny with isolated showers in the late morning and afternoon. Highs 80 to 87. East winds 25 to 30 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 71. East winds 20 to 25 mph. Chance of rain 50 percent.

Friday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 80 to 87. East winds 20 to 25 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Partly sunny. Windy. Showers likely early in the morning, then scattered showers in the late morning and afternoon. Highs 71 to 79 in the valleys to around 63 above 4000 feet. East winds 20 to 30 mph. Chance of rain 70 percent.

Tonight: Windy. Mostly cloudy with numerous showers. Lows 63 to 68 in the valleys to around 57 above 4000 feet. East winds 20 to 30 mph. Chance of rain 70 percent.

Friday: Partly sunny. Windy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 71 to 79 in the valleys to around 63 above 4000 feet. East winds 20 to 30 mph. Chance of rain 70 percent.

North Kaua’i

Today: Breezy. Partly sunny with scattered showers early in the morning, then mostly sunny with isolated showers in the late morning and afternoon. Highs 74 to 85. East winds 20 to 25 mph. Chance of rain 50 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Scattered showers. Lows 63 to 73. East winds 20 to 25 mph. Chance of rain 50 percent.

Friday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 73 to 84. East winds 15 to 25 mph. Chance of rain 50 percent.

East Kaua’i

Today: Partly sunny. Breezy. Showers likely early in the morning, then scattered showers late in the morning. Isolated showers in the afternoon. Highs 71 to 82. East winds 20 to 25 mph. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 63 to 74. East winds 15 to 25 mph. Chance of rain 50 percent.

Friday: Breezy. Partly sunny with numerous showers in the morning, then mostly sunny with scattered showers in the afternoon. Highs 70 to 83. East winds 15 to 25 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

High pressure north of the islands will bring strong trade winds the next couple of days, delivering a few windward showers, mainly night and morning. Breezy trade winds over the weekend may deliver a slight increase in showers on Sunday.

Discussion

Latest analysis features a strong 1034 mb surface high centered about 1000 miles N of the islands, and an expansive deep-layer low centered about 1500 miles to the WNW. Breezy to locally strong trade winds prevail, and are especially strong where terrain accelerates the flow. A strengthening subsidence inversion noted in 12Z sounding data is likely increasing the local acceleration of the wind over and around the terrain. A Wind Advisory remains for portions of Maui County and the Big Island, while a High Wind Warning is in effect for leeward Kohala on the Big Island, where gusts to 60 mph are expected. High clouds associated with the low continue to stream over the islands, but are expected to continue to gradually diminish today as the low moves away. Beneath the high clouds, showery low clouds are noted over waters within about 100 miles E of the islands, with radar detecting scattered to numerous showers moving rapidly W over windward portions of the islands. A little further to the E, low cloud coverage decreases to few to scattered.
The high to the N will move slowly S and change little through Friday, then shift NE and gradually weaken over the weekend. This is expected to support locally strong trade winds through Friday, with winds diminishing slightly thereafter. However, a surface trough approaching from the SE may keep the pressure gradient fairly tight into Sunday, with locally breezy trade winds generally anticipated. Guidance is honing in on a new high building NW of the islands on Monday, briefly backing winds to the NE before weakening and veering to the SE as a front approaches from the NW by midweek. Guidance understandably has been inconsistent in the long range prognosis, but there has been a trend toward the formation of yet another cutoff low along this front, with details to come later.
A ridge aloft will prevail over the next couple of days, keeping incoming moisture limited to the lowest 8-10 kft. This is deep enough to allow some showers to develop, but low enough to preclude significant rainfall accumulation. A mid- and upper-low approaching from the ESE is now expected to stall E of the islands this weekend, and a significant increase in moisture is no longer anticipated from this source. Guidance does however indicate that moisture associated with a frontal boundary now near 33N 140W will get embedded in the trade wind flow, potentially fueling an increase in trade showers Saturday night and Sunday.

Aviation

A strong high pressure system far north of the Hawaiian Islands will continue to produce windy conditions across the region. Passing showers will mainly affect windward and mountain areas with brief MVFR/IFR conditions in the stronger showers.
AIRMET Tango below 8000 ft remains in effect over and immediately southwest through northwest of mountains for tempo moderate turbulence. Strong winds will likely keep this AIRMET issued into the weekend.

Marine

High pressure centered north and northeast of the islands, along with a strong low far northwest of Kauai, will maintain these fresh to locally strong east trade winds the next couple of days. A Small Craft Advisory remains in effect for most waters to account for these strong winds and resultant high seas. High pressure will build in the wake of the low as it exits west and this will further tighten the pressure gradient over and upstream of the state, ultimately strengthening these late week easterlies. Speeds through the Pailolo and Alenuihaha Channels and south of Big Island will achieve gale force today and persist into early Saturday. Thus, a Gale Warning is in effect for these waters through Friday night.
A moderate size, medium-period northwest (310-320 degrees) swell will continue to fade through the day. A small, longer period reinforcement from the northwest moving through today will keep north and west-facing surf from completely leveling out as we head into the weekend. Strengthening trades will significantly increase short period wind driven waves along many east-facing shores. As east trade speeds peak through Friday, rough nearshore conditions along eastern shores may reach High Surf Advisory heights by tomorrow.

Fire weather

Despite a decreasing amount of low clouds approaching from the E, it does not appear that afternoon relative humidity (RH) values will diminish sufficiently today to warrant the issuance of a Red Flag Warning. However, guidance indicates drier air filtering in on Friday that could lower RH values to the point that a Warning would be required. As such, the Fire Weather Watch remains posted for Friday.

HFO Watches/Warnings/Advisories

Fire Weather Watch from Friday morning through Friday afternoon for Niihau, Kauai Leeward, Oahu South Shore, Waianae Coast, Oahu North Shore, Central Oahu, Waianae Mountains, Molokai Leeward, Lanai Makai, Lanai Mauka, Kahoolawe, Maui Leeward West, Maui Central Valley, Leeward Haleakala, Kona, South Big Island, Kohala, Big Island Interior.
Wind Advisory until 6 PM HST Friday for Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Haleakala Summit, Big Island Interior, Lanai Windward, Lanai Leeward, Maui Central Valley North, Maui Central Valley South, Big Island South, Big Island Southeast, Big Island North.
High Wind Warning until 6 PM HST Friday for Kohala.
Wind Advisory from 6 PM this evening to 6 PM HST Friday for Big Island Summits.
Small Craft Advisory until 6 AM HST Saturday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Maalaea Bay, Big Island Windward Waters.
Gale Warning until 6 AM HST Saturday for Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov