Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Sunny with scattered showers in the morning, then partly sunny with isolated showers in the afternoon. Highs around 80 near the shore to around 67 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with isolated showers. Lows around 66 near the shore to around 56 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Monday: Breezy. Mostly cloudy with isolated showers. Highs around 80 near the shore to around 68 above 3000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

South Kaua’i

Today: Mostly sunny in the morning then becoming partly sunny. Breezy. Scattered showers. Highs around 78. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 63 to 68. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Monday: Breezy. Mostly cloudy with scattered showers. Highs around 79. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Partly sunny. Occasional showers in the morning, then numerous showers in the afternoon. Highs 66 to 74 in the valleys to around 61 above 4000 feet. Northeast winds up to 15 mph. Chance of rain 90 percent.

Tonight: Breezy. Mostly cloudy with occasional showers. Lows 57 to 62 in the valleys to around 50 above 4000 feet. Northeast winds up to 20 mph. Chance of rain 90 percent.

Monday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 67 to 75 in the valleys to around 62 above 4000 feet. Northeast winds up to 25 mph. Chance of rain 70 percent.

North Kaua’i

Today: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 71 to 78. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 59 to 68. East winds up to 15 mph. Chance of rain 70 percent.

Monday: Breezy. Mostly cloudy with scattered showers. Highs 72 to 79. East winds 10 to 20 mph. Chance of rain 50 percent.

East Kaua’i

Today: Partly sunny. Breezy. Occasional showers in the morning, then scattered showers in the afternoon. Highs 71 to 78. Northeast winds 10 to 20 mph. Chance of rain 90 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then occasional showers after midnight. Lows 57 to 69. Northeast winds 10 to 15 mph. Chance of rain 90 percent.

Monday: Breezy. Mostly cloudy with scattered showers. Highs 72 to 79. Northeast winds 10 to 25 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Cool and stable moderate to locally breezy northeasterly trade winds will continue to focus showers on windward and northern slopes today. Trade winds will strengthen as high clouds thicken tonight and Monday, and an increase in rainfall is possible late Tuesday into Friday as a disturbance aloft moves slowly across the region.

Discussion

Showers remain somewhat active within a declining northeasterly trade wind flow. The trades are continuing a slow decline as a 1027 mb surface high sitting nearly 1000 miles north of Kauai weakens, and winds remain more northeasterly than normal due to the presence of a large surface low centered roughly 1500 miles to the northeast of the state. While dew points within the northeasterly flow have crept up into the lower 60s, they are still low enough to maintain a cool, winter-like feel this morning. This relatively dry flow is capped by a solid inversion between 5000 to 6500 ft, but thermal instability below the inversion continues to be extremely effective in producing shallow showers. As a result, sites on windward and northern slopes have measured 12 hour rainfall totals mostly below one quarter of an inch. Expect a slight increase in dew points today and continued windward shower activity as northeasterly winds drop a bit.
Easterly trade winds will strengthen Monday and Tuesday as surface high pressure rebuilds to the north. Dew points will recover to more typical seasonal values in the low to mid 60s, and a rather typical pattern of windward and mountain showers will prevail. The ridge aloft will break down as a sharp upper-level trough approaches from the west. Initially, the main impact will be a thickening of high clouds as early as tonight.
Wet and breezy trade winds are possible by late Tuesday and may persist into Friday. Broad surface high pressure will persist to the north, keeping the gusty trade winds in place. Meanwhile, the mid- to upper-level trough is expected to move slowly over the region. As a result, expect extensive high cloud cover to linger, along with a moistening and potential destabilizing of the air mass. This points towards a wet trade wind pattern with frequent windward showers periodically spilling over to leeward areas. A decrease in trade winds and shower activity is likely later Friday or Saturday.

Aviation

Moderate to breezy northeast trades will continue into Monday, with mainly light/brief showers moving through periodically over windward and mauka locations. Although VFR conditions will prevail, MVFR CIGS/VSBYS are possible in passing showers.

Marine

A high pressure ridge north of the Hawaiian Islands will weaken a bit today, then build north of the islands into Wednesday, and then weaken once again from Thursday onward. Trade winds will decrease slightly today as a result, then show strengthening trends from Monday into Wednesday, and then slight weakening wind speeds by the end of the week. Rough seas are expected to continue over most Hawaiian waters due to a combination of fresh to strong northeast trades, a mix of northeast wind waves and north- northeast (010 to 030 degree) swell moving through the Hawaii region. A combination of the winds and rough seas will continue to support a Small Craft Advisory (SCA) over exposed waters and channels through the first half of this week. The SCA coverage area will likely expand from Monday through Wednesday.
A large, medium-period north to northeast (010-030 degree) swell arriving from a broad gale centered around 1600 nm northeast of the state will support warning level surf for east facing shores and advisory level surf for north facing shores Monday through Tuesday. A smaller north-northwest (340-360 degree) medium period swell will also fill in today, helping to boost surf along west facing shores. A small long period south (180-210 degree) swell will build into the region with a slight bump in south shore surf activity lasting into Tuesday.
A trend back toward a more typical trade wind pattern with seas easing into the second half of next week. Surf along north and west facing shores will remain elevated through Wednesday as medium to long period northwest (300-320 degree) swell energy moves through the region. The next larger northwest (300-320 degree) swell builds in near High Surf Advisory levels along north facing shores from Thursday to Friday.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Tuesday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Channel, Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov