West Kaua’i

Tonight: Mostly clear. Breezy. Lows around 74 near the shore to around 64 above 3000 feet. Northeast winds up to 20 mph.

Monday: Sunny. Highs 84 to 89 near the shore to around 75 above 3000 feet. Northeast winds up to 15 mph.

Monday Night: Mostly clear. Lows around 73 near the shore to around 63 above 3000 feet. Northeast winds up to 15 mph.

South Kaua’i

Tonight: Partly cloudy. Breezy. Isolated showers in the evening, then scattered showers after midnight. Lows 70 to 77. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

Monday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 79 to 88. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

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

Kaua’i Mountains

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 67 to 72 in the valleys to around 61 above 4000 feet. Northeast winds 10 to 25 mph. Chance of rain 50 percent.

Monday: Breezy. Partly sunny with scattered showers. Highs 75 to 82 in the valleys to around 68 above 4000 feet. Northeast winds 10 to 25 mph decreasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

Monday Night: Partly cloudy. Breezy. Isolated showers in the evening, then scattered showers after midnight. Lows around 68 in the valleys to around 60 above 4000 feet. Northeast winds 10 to 20 mph decreasing to up to 15 mph after midnight. Chance of rain 40 percent.

North Kaua’i

Tonight: Breezy. Partly cloudy with scattered showers. Lows 65 to 75. East winds 10 to 20 mph. Chance of rain 50 percent.

Monday: Mostly sunny with scattered showers. Highs 71 to 87. East winds 10 to 15 mph. Chance of rain 40 percent.

Monday Night: Partly cloudy with isolated showers. Lows 64 to 74. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 20 percent.

East Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 66 to 77. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Monday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 78 to 86. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Monday Night: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 65 to 75. Northeast winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 40 percent.

Detailed Forecast

Synopsis

Breezy trades will continue through Monday, bringing limited showers mainly windward and mauka. An upper level low will help weaken winds and turn them out of the south Wednesday. Showers will increase as moisture increases with the potential for heavy rain across Hawaii.

Discussion

High pressure north of Hawaii and a weak disturbance passing to the south will result in breezy trade winds and stable weather through Monday. Scattered low clouds and isolated showers will move through the trade wind flow and primarily impact windward slopes, but rainfall accumulations will remain light.
Winds will weaken and veer southeasterly by late Tuesday, and south by Wednesday, as a sharp trough approaches from the northwest. A surface low will form along the trough and southerly winds will draw deep tropical moisture over the islands, while a cold pool aloft associated with the upper low will act to destabilize the atmosphere over the state. PW values will increase to around 2 inches and dewpoints will rise to around 70 Thursday and into the lower 70s Friday. As this deeper moisture moves in, heavy rain will become likely. The timing and location of the moisture is depicted slightly different in the long range models, but at this time it appears all the islands will be impacted at some point. Thus, not getting too specific in the forecast details for now, but expect an overall wetter pattern and southerly winds from around late Wednesday through at least Friday, and possibly lingering into next weekend.

Aviation

Moderate trades will continue into Tuesday with isolated showers across windward and mountain areas where short-lived MVFR conditions are possible.
Otherwise, VFR conditions will prevail across the state through Monday.
AIRMET Tango continues for moderate turbulence in downwind mountain areas.

Marine

High pressure north of the Hawaiian Islands will maintain fresh to locally strong trade winds through Monday. The Small Craft Advisory for the windier waters and channels around Maui County and the Big Island remains in effect through Monday afternoon. Thereafter, high pressure to the north weakens and trades will start to diminish. Troughing developing northwest of the islands will likely to cause winds to veer out of the southeast around midweek and bring increased shower activity for the latter half of the week.
A new small, long-period south swell will slowly fill in tonight and Monday, with a peak slightly above average Tuesday into Wednesday. Near or slightly below average surf will hold through the rest of the week be maintained by a mix of new, small south swells.
A small, medium-period northwest swell will arrive tonight and peak Monday, producing a small bump in surf through Tuesday. Surf will continue to trend up for north shores as a slightly larger long-period northwest swell peaks Wednesday. Surf may approach moderate levels late in the week as a medium-period northwest swell further increases. Surf along east facing shores will be elevated and choppy through Monday due to the locally strong trades.
A small, long-period west swell originating from Typhoon Choi-wan is forecast to reach the islands Thursday into the weekend, which may produce moderate surf for west-facing shores of the Big Island.

Fire weather

Breezy trades will continue into Tuesday with RH values just above the critical threshold for fire weather each afternoon through Tuesday. Fire weather risk then diminishes through the remainder of the week as moisture increases, winds decrease, and showers increase in coverage. The inversion should range from 6 kft to 8 kft through Monday.

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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Data Courtesy of NOAA.gov