West Kaua’i

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 69 near the shore to around 60 above 3000 feet. East winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Monday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 83 to 89 near the shore to around 76 above 3000 feet. Northeast winds up to 10 mph shifting to the west in the afternoon. Chance of rain 50 percent.

Monday Night: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 67 to 72 near the shore to around 61 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

South Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 68 to 73. Northeast winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain 50 percent.

Monday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 76 to 87. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Monday Night: Mostly cloudy with scattered showers. Lows 69 to 75. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows around 65 in the valleys to around 55 above 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Monday: Mostly cloudy. Occasional showers in the morning, then scattered showers in the afternoon. Highs 74 to 80 in the valleys to around 69 above 4000 feet. East winds up to 15 mph. Chance of rain 80 percent.

Monday Night: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows around 67 in the valleys to around 56 above 4000 feet. East winds up to 15 mph increasing to 10 to 20 mph after midnight. Chance of rain 70 percent.

North Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 62 to 72. East winds up to 15 mph. Chance of rain 50 percent.

Monday: Partly sunny with scattered showers. Highs 70 to 84. East winds up to 15 mph. Chance of rain 50 percent.

Monday Night: Mostly cloudy with scattered showers. Lows 63 to 73. East winds up to 15 mph. Chance of rain 50 percent.

East Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 64 to 74. Northeast winds around 10 mph. Chance of rain 50 percent.

Monday: Mostly cloudy with scattered showers. Highs 76 to 84. Northeast winds around 10 mph. Chance of rain 50 percent.

Monday Night: Mostly cloudy with scattered showers. Lows 65 to 75. Northeast winds up to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Moderate trades weaken giving way to land and sea breezes through early this week. Increasing moisture will move up the island chain from the southeast through the ealry portion of the week resulting in increased shower coverage over island interiors. Trades return late Wednesday and continue through the forecast period.

Discussion

Latest satellite imagery shows the sheared shortwave approaching from the north. This wave is nestled along the poleward side of the subtropical jet and will gradually sag south through tomorrow. At the surface, weak convergence and confluent easterlies centered around 850mb are focusing a plume of moisture around 10kft in depth toward portions of Windward Big Island and the adjacent waters to the south. The favorable nocturnal period should allow at least Puna and South Hilo Districts to see an increase in shower coverage tonight. Northward extent of shower coverage is in question as satellite suggests the moisture band is a touch further south than model guidance indicates.
As the aforementioned shortwave advances through the area, increasing showers will be most pronounced over the eastern end of the state through Monday then expand up the island chain by Tuesday. Trades back to northeasterly and strengthen to moderate during the early portion of the week, focusing showers windward and mauka. Breezy trades then establish during the second half of the week as the subtropical ridge strengthens north of the area.

Aviation

AIRMET Sierra is in effect for tempo mtn obsc above 2500 feet for windward Maui and windward/southeast Big Island this afternoon as clouds and showers linger at the eastern end of the state. These areas will likely remain under the AIRMET tonight as upstream moisture slowly moves in. Additional windward areas of Oahu and Molokai could be added to the AIRMET overnight. VFR conditions will prevail elsewhere with no other AIRMETs anticipated.

Marine

The trade winds have weakened into the light to moderate range today as a large North Pacific low has weakened the ridge north of the islands. The ridge will gradually restrengthen north of the state Monday and Tuesday, allowing the trades to slowly return to moderate and fresh levels. High pressure north of the islands will strengthen further by the middle to latter part of next week, bringing fresh to strong trades back to the waters. Small Craft Advisories are likely to be required for the typically windy waters around Maui and the Big Island by as early as Tuesday.
The current long-period south swell is beginning to fade this afternoon, with surf falling below advisory criteria. Surf will remain below advisory criteria tonight and Monday as forerunners from a new long-period south swell arrive, the first hints of which have just been detected on offshore buoys this afternoon. This next south swell looks to be larger than the previous, with surf expected to return to advisory levels Tuesday through Thursday. There is some potential that surf will peak close to warning levels on Wednesday.
Surf along north-facing shores will remain small through Monday, then trend slightly higher Tuesday through Friday as a pair of overlapping small north-northwest swells move through. North shore surf will drop back to nearly flat levels next weekend.
East shore surf will remain below normal through Tuesday due to lack of trade winds over and upstream of the state. Surf will trend upward Wednesday and Thursday and hold close to seasonal levels Friday through next weekend.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov