West Kaua’i

Tonight: Mostly clear with isolated showers. Lows around 73 near the shore to around 61 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Monday: Mostly sunny with isolated showers. Highs around 89 near the shore to around 77 above 3000 feet. North winds up to 10 mph shifting to the west in the afternoon. Chance of rain 20 percent.

Monday Night: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows 71 to 76 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 around 74. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Monday: Mostly sunny with isolated showers. Highs 83 to 91. East winds 10 to 15 mph. Chance of rain 20 percent.

Monday Night: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows around 74. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Partly cloudy with isolated showers. Lows 64 to 70 in the valleys to around 59 above 4000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Monday: Mostly sunny with isolated showers. Highs 77 to 88 in the valleys to around 68 above 4000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Monday Night: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows 64 to 70 in the valleys to around 60 above 4000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

North Kaua’i

Tonight: Partly cloudy with isolated showers. Lows 65 to 74. Southeast winds up to 10 mph. Chance of rain 20 percent.

Monday: Mostly sunny with isolated showers. Highs 80 to 88. East winds up to 15 mph. Chance of rain 20 percent.

Monday Night: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows 66 to 74. East winds up to 10 mph. Chance of rain 20 percent.

East Kaua’i

Tonight: Partly cloudy with isolated showers. Lows 65 to 78. Northeast winds up to 10 mph. Chance of rain 20 percent.

Monday: Partly sunny in the morning then becoming mostly sunny. Isolated showers. Highs 77 to 89. Northeast winds up to 10 mph shifting to the east in the afternoon. Chance of rain 20 percent.

Monday Night: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows 65 to 78. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Locally breezy trades deliver limited clouds and showers windward and mauka through Thursday. An uptick in showers can be expected thereafter as a batch of deeper moisture moves through the area.

Discussion

Locally breezy trades prevail beneath a stout inversion which slopes gently upward from around 5kft at Lihue to 8kft at Hilo. Shallow saturation around 3kft in depth atop the boundary layer supports isolated to scattered light showers that will increase in coverage tonight through early tomorrow morning. Flat, textureless stratocu on visible imagery are symptomatic of the resident high stability environment and will change very little during the next few days, particularly as easterly dry advection centered around 700mb reinforces existing stability.
Further north, a cold front extending from low pressure in the Gulf of Alaska is draped along and south of 40N. The long range guidance maintains solid consensus that this front will seed the trades with deeper moisture late this week as building high pressure pinches off the tail end of the front. This moisture then pivots toward the Hawaiian Islands bringing an increase in trade wind showers by week's end.

Aviation

High pressure north of the state and a weak trough to the southeast will keep moderate to breezy easterly trade winds in the forecast through Monday. Clouds and showers will favor windward and mountain areas, particularly at night, though stable conditions aloft will limit shower activity overall. VFR conditions will prevail outside of any brief passing showers.
No AIRMETs are in effect and none are anticipated to be needed through Monday.

Marine

The pressure gradient between a weak high north of the islands and an area of low pressure south of the islands will result in continued moderate to locally strong trade winds through Monday afternoon. Therefore, a Small Craft Advisory (SCA) remains in effect for the windier channels and waters surrounding Maui County and the Big Island. The high to the north will slightly weaken on Tuesday as a front moves across the North Pacific, allowing trades to briefly ease. It is expected to restrengthen by mid- week, with SCA winds likely to return at that time.
The recent small, medium period north swell will slowly decline through Monday. Another medium period north swell arrival Thursday may cause a slight bump in late week surf along north- facing shores.
A small, medium- to long-period south swell will keep surf along south-facing shores near the September average into the first part of Monday. This swell will then gradually decline late Monday through mid-week. A couple of very small reinforcements are expected throughout the week, though surf will remain small. A slightly larger, long-period swell is forecast to arrive in the islands Friday night, boosting south shore surf next weekend.
East facing shores will see typical trade wind generated energy throughout the forecast period.

Fire weather

Low humidity persists with sustained winds approaching critical fire weather thresholds for a few hours each afternoon through Monday. Expect decreasing fire weather risk from Tuesday into next weekend due to higher afternoon minimum humidity levels.

HFO Watches/Warnings/Advisories

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

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