West Kaua’i

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 85 to 91 near the shore to around 77 above 3000 feet. East winds up to 10 mph shifting to the south in the afternoon. Chance of rain 50 percent.

Tonight: Mostly clear. Isolated showers in the evening. Lows around 73 near the shore to around 61 above 3000 feet. Light winds. Chance of rain 20 percent.

Columbus Day: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 85 to 90 near the shore to around 76 above 3000 feet. Light winds. Chance of rain 40 percent.

South Kaua’i

Today: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 84 to 91. East winds 10 to 15 mph. Chance of rain 40 percent.

Tonight: Partly cloudy with isolated showers. Lows around 73. Northeast winds around 10 mph. Chance of rain 20 percent.

Columbus Day: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 82 to 90. Light winds becoming east around 10 mph in the afternoon. Chance of rain 40 percent.

Kaua’i Mountains

Today: Partly sunny with scattered showers. Highs 76 to 84 in the valleys to around 68 above 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 63 to 70 in the valleys to around 59 above 4000 feet. Light winds. Chance of rain 40 percent.

Columbus Day: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 76 to 83 in the valleys to around 67 above 4000 feet. Light winds becoming east up to 10 mph in the afternoon. Chance of rain 50 percent.

North Kaua’i

Today: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 79 to 87. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers. Lows 65 to 73. Southeast winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Columbus Day: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 78 to 87. East winds up to 10 mph. Chance of rain 40 percent.

East Kaua’i

Today: Partly sunny with scattered showers. Highs 77 to 88. East winds up to 10 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers. Lows 65 to 77. Light winds. Chance of rain 20 percent.

Columbus Day: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 76 to 87. Light winds becoming east around 10 mph in the afternoon. Chance of rain 50 percent.

Detailed Forecast

Synopsis

An upper-level low approximately 800 miles north of the islands will dig south through midweek. This will increase instability and introduce a chance for heavier showers and a few thunderstorms. East to southeast surface winds continue, becoming stronger from Wednesday into next weekend.

Discussion

Looking at radar at 3AM, a few showers are moving across the region. Nighttime Microphysics satellite imagery indicates some high clouds streaming in the from southwest. A few low-level clouds are isolated in nature and most spots are seeing relatively clear skies.
A strong upper-level low digging south toward the state will help determine our weather for the coming week. An increase in low- level mositure and instability is expected as the low gets closer. As such heavier showers and a few thunderstorms are possible Tuesday afternoon through Thursday. Conditions will remain favorable for thunderstorms through at least Friday. Models are in some disagreement as far as timing and placement of this low. This is causing some uncertainty in exactly where and when we could see heavier showers and thunderstorms. However confidence is increasing that we will most likely see some heavy showers and thunderstorms over at least the western side of the state. Details will continue to be refined in the coming forecasts.

Aviation

Light E-ESE winds have resulted in land breezes keeping skies relatively clear. Expect winds to remain light today with sea breezes developing over leeward and interior locations. A few SHRA and some low cigs with isol MVFR conds will be possible but otherwise VFR will prevail.
No AIRMETs in effect.

Marine

Broad troughing north of the islands will keep the local pressure gradient somewhat weak, maintaining mainly gentle to moderate trade winds over coastal waters into Tuesday. The trough will gradually fill in late Tuesday and Wednesday, and building surface high pressure north of 30N will drive strengthening trade winds. Small Craft Advisory conditions may develop over the typically windy waters around the Big Island and Maui as early as Wednesday night and likely by Thursday. As trades strengthen, a disturbance aloft will drift southward over the islands and bring instability.
Small to moderate northwest swell this morning will give way to a long period forerunners of a new northwest (320 deg) swell building late today and tonight. Surf should peak at High Surf Advisory levels Monday and Tuesday for most north and west shores from Kauai to Maui. Surf will gradually decline Thursday and Friday, with some small northwest swell lingering into next weekend. Tiny background south swell will prevail through the week.
A slight increase to near seasonal normal as medium-period easterly swell from a distant tropical cyclone moves across the area today. East shore surf will be small Tuesday, then increase and become rough during the second part of the week as trade winds build over and upwind of the islands.
Water levels during morning high tides will continue to gradually lower during the next couple of days. Water levels peaked just below the flooding level at most stations yesterday with conditions expected to be borderline at high tide morning.

Fire weather

Light winds and isolated showers will help maintain fire weather below critical thresholds for the next several days. Inversion heights will range from 6,000 to 7,000 feet.

HFO Watches/Warnings/Advisories

None.