West Kaua’i

Tonight: Mostly clear. Isolated showers after midnight. Lows 69 to 74 near the shore to around 62 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny with isolated showers. Highs 83 to 90 near the shore to around 75 above 3000 feet. Northeast winds up to 10 mph shifting to the south in the afternoon. Chance of rain 20 percent.

Tuesday Night: Partly cloudy with isolated showers. Lows 69 to 74 near the shore to around 62 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

South Kaua’i

Tonight: Partly cloudy with isolated showers. Lows 69 to 76. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 77 to 88. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday Night: Partly cloudy with isolated showers. Lows 70 to 76. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows around 67 in the valleys to around 59 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Tuesday: Occasional showers in the morning, then scattered showers in the afternoon. Highs 72 to 79 in the valleys to around 65 above 4000 feet. Northeast winds up to 15 mph. Chance of rain near 100 percent.

Tuesday Night: Mostly cloudy with scattered showers. Lows around 67 in the valleys to around 59 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 63 to 73. East winds 10 to 15 mph decreasing to up to 10 mph after midnight. Chance of rain 50 percent.

Tuesday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 69 to 85. East winds up to 15 mph. Chance of rain 70 percent.

Tuesday Night: Partly cloudy with scattered showers. Lows 64 to 74. East winds up to 15 mph. Chance of rain 40 percent.

East Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 66 to 76. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday: Occasional showers in the morning, then scattered showers in the afternoon. Highs 75 to 84. Northeast winds 10 to 15 mph. Chance of rain near 100 percent.

Tuesday Night: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 66 to 76. Northeast winds 10 to 15 mph decreasing to up to 10 mph after midnight. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Locally breezy trade winds will ease to moderate levels Tuesday and Wednesday, then strengthen Thursday into the weekend. Showers will continue to favor windward and mauka areas, with an uptick in moisture expected Tuesday and Wednesday.

Discussion

Locally breezy trade winds are on a gradual decline this afternoon. The surface high driving the trades remains quite strong at 1033 mb far north of Hawaii, but a weak mid-level trough just northeast of the islands is beginning to erode the local pressure gradient and resulting trades. As the trough drifts westward through tonight, trades will continue a gradual decline. Even with the mid-level trough nearby, stable conditions will persist, keeping showers focused across typical windward and mauka areas. The greatest amount of rainfall will continue to be on windward Big Island into tonight, though a band of active showers will approach by daybreak Tuesday.
A noticeable decrease in trade winds will occur Tuesday and Wednesday. The position of the surface high will change little, but the mid-level trough will drift westward over the islands, leading to a weakening of the local pressure gradient and resulting trades. Guidance suggests that moisture riding along the moderate trade wind flow will keep windward shower activity somewhat enhanced, and localized sea breezes may produce clouds and a few showers across leeward terrain each afternoon.
Trade winds should rebuild Thursday and Friday as the mid-level trough moves away. Another factor in the the restrengthening trade winds could be development of a tropical cyclone far south of Hawaii. At this time, it does not appear that any of the potential tropical cyclone activity would directly impact the islands during the coming week.

Aviation

Breezy trade winds will gradually easy through Tuesday, carrying intermittent showers into windward areas of the islands through the forecast period, most active in the overnight and early morning hours. MVFR conditions are possible under showers, though VFR is generally expected to prevail. Trade winds are expected to gradually weaken over the next few days.
AIRMET Tango remains in effect for low-level turbulence over and downwind of terrain, and is expected to continue for the next day or so as we remain under a breezy trade wind pattern.

Marine

Trade winds will gradually ease through Tuesday as the high pressure north of the islands lifts northeast and weakens. A Small Craft Advisory (SCA) has been trimmed back to the windier waters and channels around Maui County and the Big Island through tonight. The SCA will likely not be needed for any waters Tuesday as winds should have decreased to below criteria. These lighter trades should continue through Wednesday night, then may increase a bit Thursday and Friday as high pressure northeast of the islands drops a bit further south and tightens up the local pressure gradient.
The current small, long-period southwest swell has filled in will hold through tonight before gradually declining through the middle of the week. A series of overlapping small south and southwest swells will then give a small boost to the surf along south facing shores Thursday through next weekend, with perhaps a more sizable south swell moving in early next week.
Surf along east-facing shores will steadily decline through the middle of the week. Surf will then hold steady at slightly below normal levels along east facing shores late in the week through the weekend.
A series of small, long to medium period west to west-northwest swells generated by former Super Typhoon Bavi will be possible throughout the week. Otherwise, no significant north or northwest swells are expected, so surf along north-facing shores is expected to remain flat to tiny.
Peak monthly high tides combined with water levels that are running slightly higher than predicted will lead to minor flooding along the shoreline and in low-lying coastal areas. Coastal flooding is possible around the daily peak tide, which will be during the afternoon hours. A Coastal Flood Statement remains in effect through Tuesday afternoon.

HFO Watches/Warnings/Advisories

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

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Data Courtesy of NOAA.gov