Photo Credit: Brendan Stephen

West Kaua’i

Today: Sunny. Highs around 80 near the shore to around 68 above 3000 feet. East winds up to 10 mph shifting to the south around 10 mph in the afternoon.

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows around 67 near the shore to around 58 above 3000 feet. Southwest winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday: Mostly cloudy. Breezy. Scattered showers in the morning, then numerous showers in the afternoon. Highs around 82 near the shore to around 69 above 3000 feet. Southwest winds around 20 mph. Chance of rain 70 percent.

South Kaua’i

Today: Sunny. Highs 77 to 82. Light winds becoming southwest 10 to 15 mph in the afternoon.

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

Tuesday: Breezy. Partly sunny with scattered showers. Highs 78 to 83. Southwest winds 20 to 25 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Sunny. Highs 71 to 78 in the valleys to around 63 above 4000 feet. South winds up to 15 mph.

Tonight: Breezy. Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 60 to 65 in the valleys to around 56 above 4000 feet. Southwest winds 10 to 25 mph. Chance of rain 50 percent.

Tuesday: Mostly cloudy. Breezy. Scattered showers in the morning, then numerous showers in the afternoon. Highs 72 to 79 in the valleys to around 62 above 4000 feet. Southwest winds 15 to 25 mph. Chance of rain 70 percent.

North Kaua’i

Today: Sunny. Highs 71 to 80. Light winds becoming southwest up to 15 mph in the afternoon.

Tonight: Partly cloudy. Breezy. Isolated showers in the evening, then scattered showers after midnight. Lows 60 to 68. Southwest winds 10 to 20 mph. Chance of rain 30 percent.

Tuesday: Mostly sunny in the morning then becoming partly sunny. Breezy. Scattered showers. Highs 73 to 82. Southwest winds 10 to 25 mph. Chance of rain 50 percent.

East Kaua’i

Today: Sunny. Highs 72 to 81. Southwest winds up to 10 mph increasing to 10 to 15 mph in the afternoon.

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 61 to 71. Southwest winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday: Mostly sunny in the morning then becoming partly sunny. Breezy. Scattered showers. Highs 72 to 82. Southwest winds 15 to 20 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

The weather pattern starts to change back from a cool and stable weather pattern, to more southerly kona winds as a cold front approaches the islands from the northwest, warming up temperatures, and bringing up another round of unstable showers starting tonight and lasting through Wednesday. The cold front will move through the islands late Tuesday and Wednesday. Light to moderate southerly to variable winds and drier weather trend will develop from Thursday into Sunday as the stable subtropical ridge axis sets up over the island chain. Another cold front approaches the islands from the northwest and stalls just north of Kauai this weekend.

Discussion

The current cool, stable and dry weather pattern is coming to an end from tonight into Tuesday as a cold front approaches the island chain from the northwest. Variable winds will start in the morning hours with sea breeze winds becoming more southerly by afternoon. These southerly winds will strengthen through the day ahead of the approaching cold front. Southerly winds will pull up unstable tropical moisture from the south. Expect increasing clouds and showers in the forecast with the highest trends expected over island mountain and south and west slopes of all islands. Cloud tops with this event will likely be limited to around 10,000 to 12,000 feet under a mid level subsidence layer. This stability aloft should prevent any thunderstorms from developing.
Wind Threats…The current wind advisory for the Big Island summits was cancelled this morning as wind speeds are forecast to briefly decrease below advisory thresholds today. A High Wind Watch was also issued starting tonight as strong winds are expected to return to the summits of Haleakala on Maui, and Mauna Kea and Mauna Loa on the Big Island. These strong winds at summit level will likely continue through late Wednesday night as the cold front moves into the islands. If these strong wind trends continue then a High Wind Warning will replace this High Wind Watch later today. Stronger southwesterly winds aloft may produce strong gusts along north and east slopes of island mountains, as strong convective showers reach up and pull these stronger winds down the to surface in the form of wind gusts. These stronger wind gusts may require a wind advisory along these northern and eastern mountain slopes.
Prefrontal shower bands continue to show up in the latest American and European model runs in the warm and unstable air mass ahead of the frontal trough starting on Tuesday. These shower bands will develop ahead of the front and drift eastward as the front moves through the western islands.
The cold frontal cloud band will move into Kauai from Tuesday night to Wednesday morning spreading showers across the Garden Isle. Meanwhile a strong prefrontal cloud and shower band develops over Maui and Hawaii Counties on Wednesday. The cold front then dissipates over Oahu by Wednesday afternoon. All islands should see some rainfall impacts with this next system, and Oahu might see the lowest storm total rainfall amounts as compared to the other islands. Cloud tops may barely reach the highest summits on the Big Island, yet these clouds will not be high enough to produce much ice or snow along the prefrontal shower band. Temperatures will also remain too warm for any snow over the Haleakala summit on Maui.
From Thursday onward, we transition back to a drier and more stable weather pattern as the frontal trough diminishes and the subtropical ridge builds back in over the Hawaiian Islands. Light to moderate, variable to southerly winds remain in the forecast. The atmosphere will become too stable for much rainfall and local scale sea breezes may develop over each island due to relatively weak large scale winds. This drier ridge pattern will last through the weekend as the forward motion on the next approaching cold front appears to stall out just north of Kauai on Sunday.

Aviation

Wind speeds will slowly increase again today as morning sea breezes give way to more southerly winds as a front approaches from the northwest. Dry conditions will continue until this evening with isolated to scattered showers developing ahead of the approaching cold front.
VFR flight conditions will prevail statewide today. There are no AIRMETs in effect, and none are anticipated during the next 24 hours.

Marine

Light and variable winds with early morning land breezes will shift out of the southwest and strengthen into the fresh to strong category later today through Tuesday as a cold front approaches. The cold front is forecast to move down the island chain Tuesday night through Wednesday, then diminish. Light and variable winds return late Wednesday through Thursday, then strengthen out of the south on Friday as a second front passes to the north.
Surf along north and west facing shores will remain small this morning, then trend up later today as a fresh, medium-period northwest (310-320 deg) swell arrives and builds down the island chain. As this small to moderate northwest swell is peaking later today into tonight, a more significant north-northwest (350 deg) swell associated with a storm-force low centered around 1000 nm north of the state is forecast to arrive and drive the surf up to near warning levels Tuesday as it peaks. As this slowly eases Tuesday night through Wednesday, another significant, long-period northwest (310 deg) swell arriving from a developing hurricane- force low centered near the Date Line north-northwest of Midway will lead to warning-level surf for exposed north and west facing shores late Wednesday through Thursday. A gradual downward trend is expected Thursday night through Friday, with heights dipping back below advisory levels on Friday. For the upcoming weekend, guidance shows a large west-northwest (300 deg) swell arriving Saturday, then peaking Saturday night through Sunday.
Surf along east facing shores will remain small due to the lack of trades locally and upstream over the eastern Pacific. The exception will be for shores exposed to large northerly swells, which will see a rise Tuesday as the aforementioned large north swell arrives.
Surf along south facing shores will come up late tonight through midweek due to a mix of fresh to strong south-southwest winds locally and a small, long-period south swell arriving. A downward trend is expected through the second half of the week.

HFO Watches/Warnings/Advisories

High Wind Watch from this evening through late Wednesday night for Haleakala Summit, Big Island Summits.

Data Courtesy of NOAA.gov