Photo Credit: Braden Jarvis

West Kaua’i

Today: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs around 81 near the shore to around 69 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows around 67 near the shore to around 56 above 3000 feet. East winds up to 15 mph in the evening becoming light. Chance of rain 20 percent.

Saturday: Mostly sunny with isolated showers. Highs around 81 near the shore to around 69 above 3000 feet. Light winds. Chance of rain 20 percent.

South Kaua’i

Today: Partly sunny in the morning then becoming mostly sunny. Isolated showers. Highs around 80. East winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 63 to 68. Northeast winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Saturday: Mostly sunny with isolated showers. Highs around 80. Light winds. Chance of rain 20 percent.

Kaua’i Mountains

Today: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 68 to 76 in the valleys to around 63 above 4000 feet. East winds up to 10 mph. Chance of rain 30 percent.

Tonight: Partly cloudy with isolated showers. Lows 56 to 61 in the valleys to around 50 above 4000 feet. Southeast winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Saturday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 68 to 76 in the valleys to around 63 above 4000 feet. Light winds. Chance of rain 40 percent.

North Kaua’i

Today: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 73 to 80. Southeast winds up to 15 mph. Chance of rain 30 percent.

Tonight: Partly cloudy. Lows 59 to 68. Southeast winds up to 15 mph in the evening becoming light.

Saturday: Mostly sunny. Isolated showers in the afternoon. Highs 73 to 80. Light winds. Chance of rain 20 percent.

East Kaua’i

Today: Partly sunny with isolated showers. Highs 73 to 80. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 20 percent.

Tonight: Mostly cloudy with isolated showers. Lows 57 to 69. East winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Saturday: Mostly sunny with isolated showers. Highs 73 to 80. Light winds. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy east to east-southeasterly trade winds will prevail over the eastern islands, with light to moderate east-southeast trades along with leeward land and sea breezes expected over the western end of the state. Showers will focus mainly along windward and southeast slopes into Sunday. A passing upper-level trough will bring some instability today through Saturday, leading to an uptick in rainfall intensity and triggering a few showers over sheltered leeward areas in the afternoon. Winds will shift out of the south, and showers may increase late Sunday, mainly on Kauai and Oahu. A front is expected to move down portions of the island chain Monday through Tuesday, bringing the potential for heavy rainfall and thunderstorms. Another cold front could bring some more unsettled weather next Thursday.

Discussion

Currently at the surface, a weak 1011 mb low is located around 625 miles west-northwest of Kauai, with a surface trough extending both northeast and south of the low. Meanwhile, a 1033 mb high is centered around 1400 miles northeast of Honolulu. The positioning of these features is bringing east-southeasterly trade winds to the island chain early this morning, with moderate to locally breezy conditions in unsheltered sections of the eastern islands, while lighter winds prevail over the western end of the state where land breezes have developed in leeward locales. Infrared satellite imagery shows variably cloudy conditions with cloud coverage the highest over Kauai and in windward areas of the other islands. Radar imagery shows some light showers moving into windward and southeast facing slopes and coasts, with mainly dry conditions in leeward locales. Not too far west of the state scattered to numerous thunderstorms are present closer to a cold pool aloft. Main forecast concern continues to be on an incoming cold front and potential weather impacts Sunday night through early next week.
Little change in the overall wind regime is expected during the next couple days as high pressure remains anchored northeast of the state. Moderate to locally breezy east-southeast trades will persist in unsheltered sections of the eastern islands, while lighter winds prevail over the western end of the state where widespread leeward land and sea breezes will continue. Winds will gradually ease over the eastern end of the state Saturday night and Sunday, with the low level flow becoming more southerly at light to moderate speeds as a cold front begins to approach from the west. Southerly winds will continue to ramp up in advance of the front Sunday night, with breezy south to southwest winds expected Monday through Tuesday as the front moves into the islands and stalls out. The winds appear to diminish to moderate levels out of the southwest on Wednesday, with the potential for another strong surge of southwest winds, potentially very strong, in advance of yet another cold front next Thursday.
As for the remaining weather details, the east-southeasterly boundary layer flow will favor showers affecting windward and southeast facing slopes and coasts during the next several days. A few showers will be possible over leeward and interior sections of the islands each afternoon and early evening as well due to sea breeze development. A upper low/trough will approach from the west today, then move from eastward across the state tonight through Saturday night. Although the airmass will destabilize as this feature approaches and moves through, moisture return will be limited. Nonetheless, the added instability will likely increase shower coverage and intensity a bit, particularly tonight and Saturday, possibly into Saturday night, as the disturbance aloft moves through. A few thunderstorms may affect Niihau and the nearshore waters west of Kauai today and tonight, but are not expected to reach the island of Kauai.
Attention then turns to a more significant weather maker, as a cold front approaches from the west Sunday night and Monday, then slowly shifts eastward through the smaller islands Monday night and Tuesday. This will bring a rather unsettled period to the islands with widespread rainfall, heavy at times, along with embedded thunderstorms. A Flood Watch will likely be required for much if not all of the state at some point this weekend. The front is forecast to stall out and gradually dissipate in the vicinity of Maui County Tuesday night and Wednesday, keeping some lingering shower activity over the islands although the rainfall intensity should decrease. Another strong cold front appears to bring another round of showers and possibly thunderstorms to the islands next Thursday, but there is more uncertainty with this front as there remains some important model details that have yet to be resolved.

Aviation

Strong high pressure in the Northeast Pacific will keep moderate to locally breezy southeasterly winds in place through the remainder of the week. Sea breezes will predominate in the afternoons across sheltered leeward portions of Oahu, Maui, and the Big Island.
The air mass over the state will remain dry. Shower activity will be limited in both coverage and intensity, and favor southeast facing slopes and coasts. Expect mainly VFR conditions, with brief periods of MVFR under passing showers.
Brisk east winds at summit level will necessitate the continuance of AIRMET Tango for low level turbulence over and downstream of Maui and the Big Island.

Marine

Moderate to strong east to southeast winds will prevail over the eastern waters, while light to moderate east-southeast winds hold over the western waters through today. Winds will weaken slightly Saturday before veering southerly Sunday. Winds will then shift out of the south southwest and strengthen briefly to moderate to locally strong speeds during the first part of next week as a front moves down portions of the state. The combination of a large northwest swell and strong trade winds upstream will build seas to 10 feet or greater over most of the coastal waters today. The Small Craft Advisory (SCA) has been extended for most waters through 6 AM Saturday. However, some zones may drop out before then if seas ease faster than expected due to the passing northwest swell.
A high end High Surf Advisory has been extended through 6 AM Saturday for most north and west facing shores of the smaller islands. The current large, long- period northwest swell seems to have arrived later and a couple of feet bigger than expected, thus the forecast has been adjusted to hold advisory level surf through tonight. A new moderate, long-period northwest swell will build Monday, peak Monday night and Tuesday below advisory level, then gradually decline through the middle of next week.
Surf along east facing shores will remain rough and choppy through Saturday due to locally strong east to southeasterly winds and a wide fetch of strong trade winds upstream. East facing shore surf will gradually decline Sunday into early next week as the upstream trades diminish and local winds veer southerly. Surf along south facing shores will remain small through the weekend, with only background southerly swells. South shore surf could get rough and choppy Monday through the middle of next week as the southerly winds pick up.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Saturday for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala.
Small Craft Advisory until 6 AM HST Saturday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov