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Weather RadarRegional forecast
Regional Kaua`i Weather Forecast May 18, 2026
West Kaua’i
Tonight: Partly cloudy with isolated showers. Lows around 73 near the shore to around 64 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.
Monday: Breezy. Mostly sunny with isolated showers. Highs 83 to 89 near the shore to around 75 above 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.
Monday Night: Breezy. Partly cloudy with scattered showers. Lows around 71 near the shore to around 62 above 3000 feet. Northeast winds up to 20 mph. Chance of rain 50 percent.
South Kaua’i
Tonight: Mostly cloudy with scattered showers. Lows around 73. Northeast winds 10 to 15 mph. Chance of rain 50 percent.
Monday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 77 to 86. Northeast winds 10 to 20 mph. Chance of rain 50 percent.
Monday Night: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Scattered showers. Lows around 72. Northeast winds 10 to 20 mph. Chance of rain 40 percent.
Kaua’i Mountains
Tonight: Mostly cloudy with scattered showers. Lows around 68 in the valleys to around 62 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.
Monday: Mostly cloudy. Scattered showers in the morning, then showers likely in the afternoon. Highs 75 to 81 in the valleys to around 67 above 4000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 70 percent.
Monday Night: Mostly cloudy with scattered showers. Lows 65 to 70 in the valleys to around 60 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.
North Kaua’i
Tonight: Mostly cloudy with scattered showers. Lows 64 to 74. East winds up to 15 mph. Chance of rain 50 percent.
Monday: Breezy. Partly sunny with scattered showers. Highs 71 to 84. East winds up to 20 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 68 to 75. Northeast winds 10 to 15 mph. Chance of rain 50 percent.
Monday: Partly sunny with scattered showers. Highs 76 to 84. East winds 10 to 15 mph. Chance of rain 50 percent.
Monday Night: Mostly cloudy with scattered showers. Lows 67 to 74. Northeast winds 10 to 15 mph. Chance of rain 50 percent.
Detailed Forecast
Synopsis
A slightly unstable and somewhat wet trade wind flow will continue over the next few days with brief downpours possible. An increasingly stable, windy trade wind flow will develop during the second half of this week.
Discussion
Scattered heavy showers developed over select areas across the state today due to the higher than normal moisture values combined with some afternoon day time heating. As we head into the late afternoon and evening, the intensity of the showers should generally decrease. The one exception is over windward Big Island and possibly east Maui, where we are seeing frequent trade wind showers. Hilo sounding showed over 2 inches of precipitable water values this afternoon and a wet trade wind pattern could very well continue for the Big Island through the middle of the week with frequent showers over windward areas.
Overall, broad troughing aloft combined with higher than normal precipitable water values and moderate easterly trade winds will continue to produce brief downpours at times through the middle of the week. Showers will generally favor windward areas during the overnight and morning hours with scattered leeward showers developing during the afternoons. Dewpoints will continue to linger in the upper 60s to low 70s, which should make temperatures feel warmer than normal.
Increased stability and stronger trade winds are expected by Thursday. Latest global guidance from the GFS and ECMWF are in good agreement with a strong high developing far north of the state, which should result in windy conditions. Winds could very well reach Wind Advisory thresholds Thursday into Friday for select areas downstream of terrain. Drier conditions are also expected during this time, but scattered showers should continue to ride in with the windy trade winds especially during the night and early morning hours.
Aviation
Easterly tradewinds remain moderate to locally breezy and are primarily delivering showers over windward and mountain areas. Some leeward areas have also experienced isolated afternoon showers today. The afternoon showers will dissipate overnight, while windward and mountain areas can still expect intermittent showers through tomorrow. Trade winds are expected to strengthen tomorrow, and returning stability should limit showers midweek. MVFR conditions will occur within showers, and isolated IFR conditions are possible within heavier downpours. VFR will prevail elsewhere.
AIRMET Sierra is in effect for mountain obscuration for north through east sections of Oahu, the east section of Maui, and windward sections of the Big Island. Conditions over Oahu should improve this evening, while Maui and Big Island may still have conditions last overnight.
Marine
Locally fresh trades become strong during the latter half of the week. Meanwhile, stability increases limiting prospects for thunderstorms.
A small, medium-period NNW declines through tonight with surf along exposed shorelines following suit. Another medium period NNW swell will provide an additional increase in surf along N shores by early tomorrow morning. This will then be followed by another similarly sized pulse on Tuesday. Surf along W shores remains steady as NNW swell declines in favor a new long period SSW swell.
A mix of small medium to long period S swells maintains average surf along S facing shores for the next several days. The aforementioned long period SSW swell will favor increased surf along S facing shores through today. Additional medium to long period S swell arrive through the week. Meanwhile, trades maintain choppy short period surf and fresh easterly swell through the week.
Tides peak around 2.5 to 3.0 ft MLLW today. Minor overwash of low lying coastal areas will be possible during times of high tide.
HFO Watches/Warnings/Advisories
None.
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Data Courtesy of NOAA.gov
