West Kaua’i

Tonight: Mostly clear. Isolated showers in the evening, then scattered showers after midnight. Lows around 72 near the shore to around 62 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Monday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 85 to 90 near the shore to around 76 above 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Monday Night: Breezy. Mostly clear with isolated showers. Lows around 73 near the shore to around 63 above 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

South Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 71 to 76. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Monday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 80 to 89. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Monday Night: Breezy. Mostly cloudy with scattered showers. Lows around 74. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows around 67 in the valleys to around 60 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Monday: Mostly cloudy. Breezy. Occasional showers in the morning, then numerous showers in the afternoon. Highs 74 to 81 in the valleys to around 66 above 4000 feet. East winds up to 20 mph. Chance of rain 90 percent.

Monday Night: Breezy. Mostly cloudy with numerous showers. Lows around 69 in the valleys to around 61 above 4000 feet. East winds 10 to 20 mph decreasing to up to 20 mph after midnight. Chance of rain 70 percent.

North Kaua’i

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 64 to 74. East winds up to 15 mph. Chance of rain 50 percent.

Monday: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 71 to 86. East winds up to 20 mph. Chance of rain 70 percent.

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

East Kaua’i

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 67 to 75. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Monday: Mostly cloudy. Occasional showers in the morning, then scattered showers in the afternoon. Highs 76 to 85. East winds 10 to 15 mph. Chance of rain 90 percent.

Monday Night: Mostly cloudy with scattered showers. Lows 68 to 76. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy trade winds will persist through the rest of the week. Bands of low clouds and showers will periodically push across the islands, focusing primarily over windward and mauka areas during the overnight and early morning hours. A couple bands of enhanced moisture will move through the islands tonight through Thursday morning, bringing an increase in shower coverage and intensity, with some locally heavy rainfall possible. In addition, humidity levels will rise, bringing muggier conditions across the island chain.

Discussion

With a subtropical high persisting far to the northeast, moderate to locally breezy trade winds will continue throughout the week, ushering in periods of showers mainly to windward and mauka areas. The main focus for this forecast remains on potential upticks in windward and mauka showers from this evening into Monday, and again from late Tuesday into Thursday.
Looking at this afternoons satellite imagery, the leading edge of a moisture plume associated with a weak surface trough is visible just east of the Big Island. As this feature progresses westward, it will bring an uptick in windward showers to the Big Island and Maui later this afternoon, before spreading across the rest of the island chain through Monday. Some of these showers may be heavy at times, potentially leading to isolated minor flooding concerns for windward and mauka areas tonight into Monday. However, high-resolution model guidance does not currently highlight a strong potential for heavy rain as this feature passes through.
The next feature visible further upstream on satellite is a broader surface trough located about 800 miles east of the state. Stronger convection and deeper moisture make this feature look more impressive than the weak trough on the Big Islands doorstep this afternoon. This broader trough is expected to move through from Tuesday night through Thursday on the trade wind flow, bringing another uptick in windward and mauka showers. At the same time, deeper high-level clouds are expected to move over the state, which could potentially hinder shower enhancement by suppressing diurnal heating. Even so, some of these showers may be heavy at times, once again potentially leading to isolated minor flooding concerns for windward and mauka areas.
Aside from these periodic upticks in windward and mauka showers, dew points will creep up to near or slightly above 70 degrees in many locations starting tonight and persisting through much of next week, bringing muggier conditions across the state.

Aviation

Moderate to locally breezy trades are expected through Monday. Low clouds and scattered showers will move over primarily windward and mauka areas, resulting in occasional MVFR conditions. Otherwise VFR conditions are expected.
A small area of low pressure is approaching Big Island from the east this afternoon and may increase shower coverage and strength from roughly 10 PM to 2 AM HST.
AIRMET Tango is in effect for moderate turbulence downwind of terrain due to breezy trade winds and will continue through the forecast period.

Marine

A high pressure ridge far north of the Hawaiian Islands will remain anchored in place, keeping trade winds blowing across the region through much of this week. The Small Craft Advisory (SCA) has been extended through Monday, with additional areas impacted including windward waters of Oahu, Maui County and Big Island, as well as the Kaiwi Channel. This is due to brief boost in wind speeds expected to move in tonight into Monday.
The current long period south swell will maintain through Monday then gradually decline over the next few days. Another larger south swell energy pulse will arrive next weekend.
Surf along east facing shores will remain rough and choppy through the week. Surf heights along north facing shores will remain nearly flat.

HFO Watches/Warnings/Advisories

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

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Data Courtesy of NOAA.gov