West Kaua’i

Tonight: Mostly cloudy in the evening then becoming mostly clear. Isolated showers. Lows around 70 near the shore to around 60 above 3000 feet. Light winds. Chance of rain 20 percent.

Monday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 84 to 90 near the shore to around 73 above 3000 feet. Southeast winds up to 15 mph. Chance of rain 20 percent.

Monday Night: Partly cloudy with isolated showers. Lows around 71 near the shore to around 60 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

South Kaua’i

Tonight: Partly cloudy. Scattered showers after midnight. Lows around 70. Northeast winds 10 to 15 mph. Chance of rain 30 percent.

Monday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 80 to 88. East winds 10 to 15 mph. Chance of rain 50 percent.

Monday Night: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows around 71. East winds 10 to 15 mph. Chance of rain 30 percent.

Kaua’i Mountains

Tonight: Mostly cloudy with scattered showers. Lows 64 to 69 in the valleys to around 58 above 4000 feet. Light winds. Chance of rain 50 percent.

Monday: Partly sunny with scattered showers. Highs 74 to 84 in the valleys to around 66 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Monday Night: Mostly cloudy with scattered showers. Lows 65 to 70 in the valleys to around 58 above 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 64 to 72. Southeast winds up to 10 mph. Chance of rain 50 percent.

Monday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 78 to 85. Southeast winds up to 15 mph. Chance of rain 50 percent.

Monday Night: Mostly cloudy with scattered showers. Lows 65 to 72. Southeast winds up to 15 mph. Chance of rain 50 percent.

East Kaua’i

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 64 to 75. North winds up to 10 mph. Chance of rain 50 percent.

Monday: Partly sunny with scattered showers. Highs 75 to 86. East winds up to 15 mph. Chance of rain 50 percent.

Monday Night: Mostly cloudy with scattered showers. Lows 65 to 75. East winds up to 15 mph becoming around 10 mph after midnight. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Light to moderate trade winds trade winds will shift out of the east to east-southeast Monday and Tuesday as a surface trough develops several hundred miles northwest of Kauai. Pockets of moisture moving along the trade wind flow will focus showers over typical windward slopes, while daytime sea breezes bring some chances for leeward showers on Monday and Tuesday afternoon. Trade winds will gradually strengthen Wednesday through Friday and likely be breezy next weekend.

Discussion

A rather stable, light to moderate trade wind flow remains in place this afternoon. A surface trough lies between Hawaii and somewhat strong high pressure farther north, causing the local pressure gradient and resulting trade winds to weaker than usual, and a mid-level ridge sitting over the islands is maintaining stable conditions with an inversion based near 7,000 ft. A narrow slot of reduced moisture is producing minimal rainfall along windward areas this afternoon, and aside from scattered showers over the Kona slopes of the Big Island and Ulupalakua area of Upcountry Maui, leeward areas are dry. Shower activity over leeward Maui will dissipate quickly around sundown and will diminish overnight on the Big Island. Shower activity over windward areas will remain light, with the exception of a possible uptick near Kauai and Oahu near sunrise.
Subtle changes are expected Monday and Tuesday. A surface trough will develop roughly 600 miles northwest of Kauai and cause local trade winds to veer out of the east to east-southeast, possibly causing afternoon leeward sea breezes to be more extensive on Kauai and Oahu. The inversion will weaken over these islands as well, suggesting higher chances for afternoon showers over leeward terrain.
Trade winds will strengthen and shift back to a more typical direction Wednesday through Thursday as low pressure to the northwest fills and surface high pressure builds far northeast of Hawaii. A stable, moderate to locally breezy trade wind flow will bring typical rainfall to mainly windward areas. Breezy trades are favored for next weekend.

Aviation

A hybrid sea breeze and light to moderate trade wind pattern will continue through tonight, with afternoon sea breezes giving way to land breezes tonight along terrain-sheltered western slopes. Trade wind speeds will gradually increase through the day Monday, becoming locally breezy over the eastern half of the island chain by Monday night. Relatively dry conditions will continue, with brief passing showers possible over windward and mountain areas, favoring the overnight through early morning hours. VFR conditions will prevail. No AIRMETs are in effect, nor expected through 24 hours.

Marine

A high pressure ridge will remain far north of Hawaii over the next several of days, then set up northeast of the state towards the end of the week. A trough developing northwest of the state will briefly cause the trade winds to veer toward the east- southeast on Monday. As the trough moves away, trades will gradually strengthen Tuesday into Wednesday with moderate to locally strong trade winds returning by the middle of the week. Small Craft Advisory could return to the typical windy areas around Maui County and the Big Island as early as Tuesday or Wednesday. As the ridge strengthens, widespread fresh to strong trade winds are possible this weekend.
The current south-southwest (200 degree) swell peaked last night into this morning and will continue to slowly decline through the middle of the week. A small south-southwest swell is possible Friday into the weekend.
Surf along east facing shores will remain moderate as the short- period northeast swell holds through Monday. Trade winds will gradually strengthen throughout the week, which will bring an increase of rough and choppy waves towards the second half of the week. Windswell will continue to increase over the weekend due to strong trade winds.
A trough located north of the state could produce small short- period energy out of the north Tuesday through the middle of the week.

HFO Watches/Warnings/Advisories

None.

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