Photo Credit: Brendan Stephen

West Kaua’i

Today: Mostly sunny with isolated showers. Highs 76 to 83 near the shore to around 67 above 3000 feet. Northeast winds up to 10 mph in the morning becoming light. Chance of rain 20 percent.

Tonight: Mostly clear. Lows 60 to 65 near the shore to around 52 above 3000 feet. Northeast winds up to 10 mph in the evening becoming light.

Wednesday: Sunny. Isolated showers in the afternoon. Highs 76 to 82 near the shore to around 68 above 3000 feet. Light winds becoming west up to 10 mph in the afternoon. Chance of rain 20 percent.

South Kaua’i

Today: Mostly sunny. Highs 74 to 82. Northeast winds 10 to 15 mph.

Tonight: Mostly clear. Lows around 63. Northeast winds 10 to 15 mph.

Wednesday: Sunny. Highs 74 to 82. Northeast winds 10 to 15 mph decreasing to up to 10 mph in the afternoon.

Kaua’i Mountains

Today: Partly sunny in the morning then becoming mostly sunny. Isolated showers. Highs 67 to 73 in the valleys to around 59 above 4000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 53 to 62 in the valleys to around 51 above 4000 feet. Northeast winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Wednesday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 68 to 75 in the valleys to around 60 above 4000 feet. Light winds. Chance of rain 30 percent.

North Kaua’i

Today: Mostly sunny. Highs 69 to 77. Northeast winds up to 15 mph.

Tonight: Mostly clear with isolated showers. Lows 56 to 65. Southeast winds up to 10 mph. Chance of rain 20 percent.

Wednesday: Sunny. Isolated showers in the afternoon. Highs 70 to 78. East winds up to 10 mph. Chance of rain 20 percent.

East Kaua’i

Today: Mostly sunny. Highs 67 to 79. North winds 10 to 15 mph.

Tonight: Partly cloudy with isolated showers. Lows 56 to 67. North winds around 10 mph. Chance of rain 20 percent.

Wednesday: Sunny. Highs 68 to 80. Northeast winds up to 10 mph.

Detailed Forecast

Synopsis

A very stable, breezy northeasterly flow will bring an increase in light shower activity over the eastern half of the island chain today through Wednesday as a shallow band of moisture continues to move south. Weak easterly trade winds will develop Wednesday and prevail into Thursday, and a passing disturbance aloft may trigger spotty showers. Moderate trade winds and a typical pattern of windward rainfall is expected Friday through the weekend.

Discussion

Satellite and radar imagery shows a band of moisture moving through Maui County, producing scattered light rainfall with rates generally under 0.25 inches per hour. This band of moisture is expected to continue to really fill in over the Big Island later this afternoon and linger through Wednesday. Despite a shortwave aloft passing overhead, a mid level ridge should cap cloud depth below 10,000 ft and limit shower intensity. The reasonable worst case ensemble guidance is showing total rainfalls of less than 1 inch across terrain, which suggests modest rainfall. A stable north to northeasterly surface flow will focus rainfall along northeasterly slopes with a few light showers making it over to leeward areas. Dew points along the band will briefly rebound into the low to mid 60s, raising overnight low temperatures back around normal. Elsewhere of the band, clouds and chances of showers will be minimal and dew points will drop back in the upper 50s, allowing overnight lows to drop slightly below February normal.
Kilauea volcano showed some activity overnight within the Halemaumau cater where excess volcanic gases are being released and is the primary concern. Thus, vog has been introduced back into the forecast based on current and future wind trajectories.
Weak trade winds will develop Wednesday and hold through Thursday as a surface ridge to the north is eroded by an approaching front from the northwest. The GFS and ECMWF shows this front stalling before reaching the area. However, a passing shortwave aloft associated with the front may produce instability. Since sea breezes will likely overpower the weak trades, there is some chance that afternoon convection could produce spotty rainfall. The ECMWF has been keeping the moisture from this current band pooling around the state through Thursday that could fuel enhanced showers, while the GFS has been drying the area out and not picking up on a significant increase in moisture. Thus, there is some uncertainty on shower potential.
Easterly trade winds will build to moderate strength on Friday and Saturday as a surface ridge expands north of the state. A typical pattern of windward and mauka showers is expected through the weekend.

Aviation

An old frontal band will bring some light showers and MVFR cigs/vsbys as it moves through the islands today and tonight. The sub VFR conditions will remain confined to north facing slopes and coasts, with VFR prevailing in leeward areas.
AIRMET Sierra is now in effect for mountain obscuration across windward sections of Kauai, Oahu, Molokai and Maui. Improving conditions are possible later today.
AIRMET Tango is now in effect for moderate upper level turb across Oahu and Kauai. This AIRMET will likely be expanded to include Maui County later this morning and the Big Island this afternoon.

Marine

Moderate to locally fresh north-northeast winds are expected through the day as the high northwest of the state slowly tracks southeastward and drifts closer to the state. Winds will gradually veer to the east and weaken tonight through Thursday. The ridge of high pressure should be very close to the state by Thursday, which should allow for light to gentle winds. The ridge of high pressure should lift northward Friday through the weekend, which should bring the return of fresh to locally strong trade winds over the weekend.
The current moderate to large medium period north to north- northeast swell will remain moderate to large today. A slight reinforcement overnight from the north-northeast has resulted in the extension of the High Surf Advisory (HSA) for most north facing shores and the Small Craft Advisory (SCA) due to seas of 10 feet or greater for exposed waters and channels across the state through 6 pm HST today. Lastly, a Marine Weather Statement (MWS) remains for Maui County windward waters and Big Island windward waters in regards to north facing harbors such as Kahului and Hilo through the day because of the north- northeast swell.
A new moderate long period west-northwest swell is expected to fill in today, peak this afternoon before slowly declining Wednesday. A slightly larger long- period northwest swell is expected to fill in late Thursday and peak on Friday near High Surf advisory thresholds.
Surf along east facing shores should continue to see moderate surf throughout the week due to the long-lived north-northeast to northeast swells throughout the week. A reinforcing northeast swell is expected around Thursday, which could elevate surf along east facing shores near advisory thresholds. Surf along south facing shores will remain tiny through the forecast period with mainly background energy.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST this evening for Niihau, Oahu North Shore, Olomana, Maui Windward West, Kauai North, Kauai East, Koolau Windward, Molokai Windward, Molokai North, Maui Central Valley North, Windward Haleakala, Big Island East, Big Island North.
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, Alenuihaha Channel, Big Island Windward Waters.

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