West Kaua’i

Tonight: Partly cloudy. Isolated showers after midnight. Lows around 64 near the shore to around 54 above 3000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Saturday: Mostly sunny. Breezy. Isolated showers in the morning. Highs around 79 near the shore to around 66 above 3000 feet. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Saturday Night: Partly cloudy. Lows around 64 near the shore to around 54 above 3000 feet. Northeast winds 10 to 15 mph.

South Kaua’i

Tonight: Partly cloudy. Breezy. Isolated showers in the evening, then scattered showers after midnight. Lows around 64. Northeast winds 15 to 20 mph. Chance of rain 30 percent.

Saturday: Mostly sunny. Breezy. Scattered showers in the morning. Highs 73 to 80. Northeast winds 15 to 25 mph. Chance of rain 40 percent.

Saturday Night: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Isolated showers. Lows around 63. Northeast winds 15 to 20 mph. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then showers likely after midnight. Lows 56 to 62 in the valleys to around 51 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Saturday: Partly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 65 to 72 in the valleys to around 57 above 4000 feet. Northeast winds 10 to 20 mph decreasing to up to 20 mph in the afternoon. Chance of rain 50 percent.

Saturday Night: Breezy. Mostly cloudy with scattered showers. Lows 56 to 61 in the valleys to around 51 above 4000 feet. Northeast winds up to 20 mph. Chance of rain 40 percent.

North Kaua’i

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then showers likely after midnight. Lows 57 to 66. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Saturday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 68 to 77. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Saturday Night: Breezy. Mostly cloudy with isolated showers. Lows 57 to 66. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

East Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 58 to 68. North winds 10 to 20 mph. Chance of rain 50 percent.

Saturday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 66 to 77. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Saturday Night: Breezy. Mostly cloudy with isolated showers. Lows 57 to 68. North winds 10 to 20 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy northeasterly trade winds will focus clouds and showers over windward and mauka areas with brief heavier showers possible. A drier airmass will filter over the western half of the state by Saturday afternoon, while showery conditions could persist over the windward areas of the eastern half of the state. Drier, cooler air will fill in state wide by Sunday. Trade winds will strengthen over the next 24 hours, becoming locally strong by Saturday evening. Gusty winds are expected over leeward areas this weekend.

Discussion

Satellite imagery this afternoon shows a lingering band of moisture in the form of a cluster of clouds with embedded showers just upstream of Maui County. Scattered clouds with light to a few brief moderate showers can been seen on radar focusing mainly along the windward and mauka areas as well as the Kona coast of the Big Island where a seabreeze has developed. The next band of showers associated with a remnant frontal boundary is just 150 sm north of Kauai County. Forecast remains on track with chances of showers increasing tonight mainly along windward and mauka areas as the band of showers moves south over Kauai tonight and converges with the lingering band of moisture over Maui County before pushing over the Big Island through the day Saturday. Upper level troughing over the central islands will help enhance showers under the trade wind inversion. Heavier showers are likely along windward and mauka areas of Maui County and the Big Island given the location of greatest upper level support and moisture availability. Kauai and Oahu will see moderate showers with the passage of the front however brief heavy showers cannot be entirely ruled out either. Not anticipating any significant flooding threats.
A strong pressure gradient will build north of state as a surface high develops to the northwest and a surface low strengthens to the northeast. This gradient will send very breezy northeasterly winds following behind the remnant frontal boundary and will help keep persistent clouds and showers along windward areas. Inversion heights may drop to around 5,000 ft Saturday around Kauai and Oahu as upper level ridging generates more subsidence that could lead to enhance downsloping winds on leeward sides of north facing ridges. Wind gusts of 40 mph will be possible with gusts up to 50 mph not out of the question. Depending on how strong the wind gusts become during the day Saturday, a Wind Advisory may be needed over select leeward areas for Saturday evening into Sunday. Thus will continue to monitor latest observations and guidance.
Temperatures will drop a couple of degrees by Saturday morning and dewpoints will drop in the 50's west of the the Big Island. This cooler and drier airmass will spread state wide Sunday limiting tradewind showers.
Gusty northeasterly winds will gradually ease Monday before shifting more easterly as a surface high tracks north of the state and the low pressure system moves far northeast of the state. A more typical easterly trade wind pattern of scattered showers across the windward and mauka slopes is expected through much of next week.

Aviation

Band of showers and attendant MVFR conditions that passed over Oahu this morning will reach Windward Maui this evening and the Big Island during Saturday. AIRMET Sierra for mountain obscuration may be needed for windward and mauka areas of these islands as the band of showers advances eastward.
Moderate NNE trades hold through much of the night and then rapidly strengthen early Saturday in response to deepening low pressure northeast of the state. Strong and gusty NNE trades then expected Saturday into Saturday night.

Marine

A low pressure system northeast of the islands will interact with high pressure building in from the northwest to strengthen the northeasterly trade winds to fresh to strong speeds through early next week. The current Small Craft Advisory covering the leeward waters and channels around the smaller islands will expand to encompass the waters around the Big Island on Saturday as the stronger winds progress down the island chain.
Another small medium-period northwest swell began filling in earlier today, and combined with the fading small short-period northeast wind swell, will help to maintain small surf across north-facing shores into Saturday. The aforementioned small northeast short-period swell will also bring slightly below average surf to east-facing shores into Saturday. As the trades strengthen on Saturday surf heights will build slightly along east-facing shores.
A deepening low to the northeast will send a large medium-period swell (360 degrees veering to 040 degrees) to north- and east- facing shores Sunday through early next week, with High Surf Advisory conditions looking likely.
Along south-facing shores, small background pulses will keep surf heights above flat conditions through early next week, with a slight bump possible on Saturday.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Sunday for Kauai Northwest Waters, Kauai Leeward Waters, Kauai Channel, Oahu Leeward Waters, Kaiwi Channel, Maui County Leeward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel.
Small Craft Advisory from 6 AM Saturday to 6 AM HST Sunday for Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov