West Kaua’i

Tonight: Partly cloudy with isolated showers. Lows around 68 near the shore to around 58 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Monday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 81 to 88 near the shore to around 74 above 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Monday Night: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 66 to 71 near the shore to around 59 above 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

South Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows around 68. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Monday: Partly sunny with scattered showers. Highs 79 to 86. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Monday Night: Mostly cloudy. Scattered showers in the evening, then showers likely after midnight. Lows around 69. East winds 10 to 15 mph. Chance of rain 70 percent.

Kaua’i Mountains

Tonight: Mostly cloudy with occasional showers. Lows 60 to 68 in the valleys to around 57 above 4000 feet. East winds 10 to 15 mph. Chance of rain 80 percent.

Monday: Mostly cloudy. Occasional showers in the morning, then showers likely in the afternoon. Highs 73 to 79 in the valleys to around 64 above 4000 feet. East winds 10 to 15 mph. Chance of rain 80 percent.

Monday Night: Showers likely in the evening, then occasional showers after midnight. Lows 60 to 69 in the valleys to around 58 above 4000 feet. East winds 10 to 15 mph. Chance of rain near 100 percent.

North Kaua’i

Tonight: Mostly cloudy with numerous showers. Lows 62 to 70. East winds 10 to 15 mph. Chance of rain 70 percent.

Monday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 74 to 84. 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 showers likely. Lows 62 to 70. East winds 10 to 15 mph. Chance of rain 70 percent.

East Kaua’i

Tonight: Mostly cloudy with numerous showers. Lows 62 to 72. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Monday: Partly sunny with numerous showers. Highs 72 to 84. East winds 10 to 15 mph. Chance of rain 70 percent.

Monday Night: Mostly cloudy with showers likely. Lows 63 to 73. East winds 10 to 15 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Breezy trade winds will continue for the next couple of days, with passing clouds and showers favoring windward and mauka areas. Lighter winds are expected by the middle of the week with fewer windward showers and a greater chance for afternoon interior showers each afternoon.

Discussion

The diurnal trend has taken its toll on the batch of moisture that was positioned over Maui County this morning. Now focused over Oahu, little remains aside from a few isolated showers. Suspect coverage will begin to increase again during the next few hours bringing an uptick in showers to Windward Oahu and, more likely, Windward Kauai by late tonight. Water vapor and model analysis indicates diminished stability over the western end of the state associated with a weak upper low and left exit region of the attendant 100kt upper jet. This is contributing to diminished instability from Kauai through Oahu as evidenced by steepening lapse rates on this afternoon's sounding out of Kauai. As showers redevelop tonight, a few heavier showers may develop in the vicnity of Kauai. Otherwise, this upper low will slowly drift eastward across the state through Tuesday contributing to a slow eastward spreading of weak instability. Upstream visible imagery suggests a steady supply of shallow moisture which will favor continued showers over windward and mauka areas through early this week. Any particularly organized pockets of moisture may contain locally heavy showers.
Tuesday through at least early Wednesday will be characterized by mid-level shortwave ridging developing in response to a digging mid- latitude trough that will impinge on the area late Wednesday through Friday. This period of ridging will bring a brief period of increased stability as the surface pressure gradient diminishes. As a consequence, a transition to a land and sea breeze pattern is anticipated no later than Wednesday as mid-level stability begins to weaken. Large scale ascent is then maximized Thursday through Friday and afternoon showers over island interiors are likely to gain appreciable depth likely resulting in pockets of heavy downpours each afternoon. Light winds continue into the weekend as mid-level forcing diminishes resulting in either a land/sea breeze pattern with more muted diurnal convection or a hybrid sea breeze pattern which will tend to focus showers over western slopes of each island.

Aviation

Breezy trade winds will continue through Monday. Scattered low clouds and showers will track in with the trade wind flow, and most active in the late night and morning hours and favor windward slopes and coasts.
AIRMET Tango is in effect for tempo moderate turbulence below 8000 feet over leeward sides of all Hawaiian islands. AIRMET Tango is also posted for jet stream turbulence over Hawaii between FL280 and FL380.

Marine

High pressure northeast of the state will maintain moderate to strong trades through Monday. As a result, a Small Craft Advisory (SCA) remains in effect for the typically windy waters around Maui and the Big Island through 6 PM Monday. The trades will gradually ease Tuesday and Tuesday night, then become further disrupted Wednesday and Thursday as a front approaches the state from the northwest. Winds will become light and variable over the western waters as a result, while winds over the eastern half of the island chain shift out of the east-southeast at light to moderate speeds.
East shore surf will remain at or just above average through Tuesday, and will be rather rough due to the strong trades, particularly through Monday. As the trades diminish during the second half of the week, surf along east facing shores will drop below normal.
A small to moderate sized northwest swell will give a boost to surf along north and west facing shores Monday and Tuesday, followed by a decline Wednesday and Thursday. A new moderate-sized north-northwest swell will arrive late Thursday, potentially bringing advisory level surf to north and west facing shores Friday, then lowering next weekend.
Surf along south facing shores will remain small and mostly at background levels through late next week.

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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