West Kaua’i

Tonight: Partly cloudy. Isolated showers after midnight. Lows around 65 near the shore to around 55 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Tuesday: Partly sunny. Breezy. Isolated showers in the morning. Highs around 83 near the shore to around 70 above 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Tuesday Night: Mostly cloudy. Isolated showers after midnight. Lows around 68 near the shore to around 57 above 3000 feet. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 20 percent.

South Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows around 65. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday: Partly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 75 to 82. East winds 15 to 20 mph. Chance of rain 40 percent.

Tuesday Night: Mostly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 67. East winds 10 to 15 mph. Chance of rain 40 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then scattered showers after midnight. Lows around 62 in the valleys to around 53 above 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Tuesday: Breezy. Mostly cloudy with scattered showers. Highs 70 to 80 in the valleys to around 62 above 4000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Tuesday Night: Mostly cloudy with scattered showers. Lows around 64 in the valleys to around 55 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 59 to 67. East winds up to 10 mph. Chance of rain 50 percent.

Tuesday: Mostly cloudy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 74 to 83. East winds up to 15 mph. Chance of rain 40 percent.

Tuesday Night: Mostly cloudy with scattered showers. Lows 61 to 69. East winds up to 15 mph. Chance of rain 40 percent.

East Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 60 to 69. Northeast winds around 10 mph. Chance of rain 50 percent.

Tuesday: Mostly cloudy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 70 to 81. East winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday Night: Mostly cloudy with scattered showers. Lows 63 to 71. East winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

High pressure building north of the state will strengthen trade winds into the moderate to locally breezy range through Wednesday. Brief passing showers will favor windward and mountain areas, mainly during the overnight and early morning hours. From Thursday into the weekend, winds will ease slightly and veer to a more east-southeast direction, shifting shower activity toward southeast-facing slopes of the Big Island and Maui, as well as some interior areas. Overall rainfall amounts are expected to remain limited.

Discussion

The broad band of high- and mid-level clouds currently over the islands, tied to a weakening upper-level disturbance and deeper moisture plume, will continue to thin and gradually clear through tonight. As this feature departs, high pressure building to the northeast will tighten the local pressure gradient, strengthening easterly trade winds into the moderate to locally breezy range through Wednesday. This will usher in drier air and a more stable airmass statewide by midweek.
By Thursday, winds will ease slightly and veer more east- southeast as the surface high shifts farther northeast and a cold front approaches from the northwest. Model guidance remains in good agreement that the front will draw closer late in the week but likely stall west of the islands. The boundary is then expected to lift northward over the weekend as a deep low tracks well northwest of the state. As the large-scale flow weakens during this period, local sea breezes will likely develop along terrain-sheltered slopes. Shower activity should remain limited through the end of the week, with mainly brief passing showers.
Looking ahead to early next week, another front approaching from the west could bring the next opportunity for more widespread unsettled weather as southerly flow develops. Details will continue to be refined over the coming days.

Aviation

Trade winds have begun to gradually return across the state today at light to moderate speeds. Expect these trade winds to continue strengthening tomorrow. Mid to high level clouds are still over the islands from Oahu to the Big Island, but will continue to move out of the area through tonight. Expect brief showers to start focusing over typical windward and mountain areas, with MVFR conditions expected within showers and VFR conditions elsewhere.
AIRMET Tango is in effect across the islands for upper level moderate turbulence between FL280-FL360. AIRMET Tango is also in effect for mid level moderate turbulence from Oahu to Big Island between 140-FL200. The mid level turbulence will likely weaken by this evening, while the upper level turbulence will likely continue through most of tonight, but on a weakening trend. Light icing is possible in a layer between 130-FL230 due to the mid- upper level clouds currently over the state.

Marine

A Small Craft Advisory is now in effect for the typically windy channels and waters around Maui County and the Big Island as trade winds are forecast to increase tonight in response to strengthening surface high pressure to the north. Winds will become fresh to locally strong by Tuesday night, which expands the area that the Small Craft Advisory is in effect for into the windward waters of Maui and the Big Island through Wednesday evening. Winds maintain strength but veer east-southeast towards the end of the week as another front approaches from the west and the surface high to the north of the state shifts eastward.
Surf along north- and west-facing shores will remain slightly elevated tonight (but still below advisory levels) as a moderate, medium period northwest swell (310 degrees) continues to impact the islands. Surf along north- and west-facing shores will then gradually decrease through the morning into Tuesday and remain small though the rest of the week, with another small northwest bump expected late this week into the weekend.
A short period northeast (40 degrees) swell will fade tonight and be replaced by increasing, short period choppy conditions as fresh trade winds redevelop and expand upstream of the state. This will keep surf along exposed east-facing shores somewhat elevated.
Surf along south-facing shores will remain small to tiny, with no significant swells forecast for at least the next several days.

HFO Watches/Warnings/Advisories

Small Craft Advisory from 6 PM Tuesday to 6 PM HST Wednesday for Maui County Windward Waters, Big Island Windward Waters.
Small Craft Advisory until 6 PM HST Wednesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov