Photo Credit: Braden Jarvis

West Kaua’i

Rest Of Today: Breezy. Partly sunny with scattered showers and isolated thunderstorms. Highs around 83 near the shore to around 73 above 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Breezy. Isolated thunderstorms and showers in the evening, then scattered showers and isolated thunderstorms after midnight. Lows 67 to 72 near the shore to around 58 above 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Wednesday: Breezy. Mostly sunny with isolated showers. Highs around 84 near the shore to around 74 above 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

South Kaua’i

Rest Of Today: Cloudy in the morning then becoming partly sunny. Breezy. Showers and isolated thunderstorms in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs around 81. Northeast winds 10 to 25 mph. Chance of rain 90 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers and isolated thunderstorms in the evening, then numerous showers and isolated thunderstorms after midnight. Lows 65 to 71. Northeast winds 10 to 25 mph. Chance of rain 70 percent.

Wednesday: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 82. Northeast winds 15 to 25 mph. Chance of rain 60 percent.

Kaua’i Mountains

Rest Of Today: Breezy. Showers and isolated thunderstorms. Highs around 76 in the valleys to around 65 above 4000 feet. East winds 10 to 20 mph. Chance of rain near 100 percent.

Tonight: Breezy. Mostly cloudy with numerous showers and isolated thunderstorms. Lows around 61 in the valleys to around 53 above 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Wednesday: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 77 in the valleys to around 66 above 4000 feet. East winds 10 to 20 mph. Chance of rain 60 percent.

North Kaua’i

Rest Of Today: Mostly cloudy. Showers and isolated thunderstorms in the morning, then numerous showers and isolated thunderstorms in the afternoon. Highs 76 to 82. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 90 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers and isolated thunderstorms in the evening, then numerous showers and isolated thunderstorms after midnight. Lows 61 to 70. East winds up to 20 mph. Chance of rain 70 percent.

Wednesday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 77 to 83. East winds up to 15 mph. Chance of rain 50 percent.

East Kaua’i

Rest Of Today: Showers and isolated thunderstorms in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs 74 to 80. Northeast winds 10 to 15 mph. Chance of rain near 100 percent.

Tonight: Mostly cloudy. Scattered showers and isolated thunderstorms in the evening, then numerous showers and isolated thunderstorms after midnight. Lows 59 to 72. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Wednesday: Mostly cloudy with numerous showers in the morning, then mostly sunny with scattered showers in the afternoon. Highs 75 to 81. Northeast winds 10 to 15 mph. Chance of rain 60 percent.

Detailed Forecast

Synopsis

A weakening upper low near Kauai will keep wet easterly trade winds in the forecast into Wednesday morning with locally heavy showers possible and isolated afternoon thunderstorms over the Big Island. Expect shower coverage to slowly decrease through the day with typical trade wind weather expected from Wednesday into Friday. Increasing shower trends return by this weekend as another weak upper low forms just north of the state. Easterly trade winds will continue to blow across the region through much of next week.

Discussion

Shower activity has trended upward across the Hawaii region this morning as shown on the latest local radar and satellite imagery. These trends follow the typical diurnal cycle of peak rainfall amounts during the early morning hours under the unstable influence of an upper level low near Kauai.
In the short term, this upper low will continue to enhance trade wind shower activity with decreasing chances for heavy showers and thunderstorms through tonight. Isolated thunderstorms will linger mainly over Kauai through tonight, and over the Big Island slopes in the afternoon hours.
A weak high pressure ridge will build over the island chain from Wednesday into Friday. This ridge aloft will produce stronger subsidence (downward moving air), and strengthen (lower) the trade wind temperature inversion heights into the 5,000 to 7,000 foot range across the region. Brief trade wind showers will favor windward and mountain areas mainly during the overnight to early morning hours.
The longer range forecast continues to show subtle changes towards increasing shower trends from Friday night through this weekend as a weak upper low/trough forms just north of the state. How much shower activity will highly depend upon the strength of this upper level feature. Confidence is only moderate that increasing shower trends will be noticeable in our island trade wind weather pattern. Additional opportunities remain for periods of enhanced showers in next week's weather forecast picture. Stay tuned.

Aviation

High pressure northeast of the state will keep moderate to breezy trade winds in place during the next 24 hours. The airmass will remain unstable due to troughing aloft, resulting in a more showery trade wind pattern, particularly for windward areas. A thunderstorm or two could pop on the Big Island slopes this afternoon as well. A more stable and drier airmass should begin to build into the islands tonight.
AIRMET Sierra remains in effect for Kauai, Oahu, Molokai, Maui and the Big Island. This AIRMET will likely remain in place through much of the morning. AIRMET Tango remains in effect for moderate upper level turbulence over the eastern half of the state. This AIRMET will likely remain in effect today. AIRMET Tango may also be needed for moderate low level turbulence over and downwind of the terrain beginning late today or tonight.

Marine

Trade winds have returned due to high pressure building far northeast of the state, and should hold through the week. Small Craft Advisory level winds (25 kt) will persist over the windier waters around Maui County and the Big Island. The advisory may need to be expanded to Kaiwi Channel waters tonight into Wednesday. Winds may lower slightly by this weekend as the ridge settles southward and weakens.
Surf along east facing shores will steadily rise today due to the trades that have returned locally and upstream across the eastern Pacific. Guidance shows this holding into the second half of the week before easing next weekend as the trades upstream trend down.
The quiet conditions across the northern Pacific continues through the first week of April, with minimal swell anticipated. This will translate to the nearly flat conditions continuing for north and west facing shores. The exception will be for north facing shores exposed to trade wind energy wrapping in, which could generate some small surf for the typical standout locations this week. For the extended, there is a potential for a short/medium period northerly swell associated with a decent sized area of north-northwest winds setting up and expanding southward from the Aleutians around the Date Line Friday through Saturday. If this materializes, this swell would arrive locally early next week and linger through midweek.
For south facing shores, guidance supports the small conditions continuing well into April with mainly background energy moving through.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Wednesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov