West Kaua’i

Tonight: Mostly cloudy with scattered showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows around 73 near the shore to around 63 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Saturday: Breezy. Partly sunny with scattered showers and slight chance of thunderstorms in the morning, then mostly sunny with isolated showers in the afternoon. Locally heavy rainfall possible in the morning. Highs around 88 near the shore to around 77 above 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Saturday Night: Partly cloudy with scattered showers. Lows 71 to 76 near the shore to around 62 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

South Kaua’i

Tonight: Mostly cloudy. Breezy. Showers likely and slight chance of thunderstorms in the evening, then occasional showers and slight chance of thunderstorms after midnight. Locally heavy rainfall possible. Lows around 74. Northeast winds 15 to 20 mph. Chance of rain 90 percent.

Saturday: Mostly cloudy. Breezy. Occasional showers and slight chance of thunderstorms in the morning, then scattered showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 81 to 89. Northeast winds 15 to 20 mph. Chance of rain 90 percent.

Saturday Night: Mostly cloudy with showers likely. Lows around 74. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Kaua’i Mountains

Tonight: Breezy. Occasional showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 65 to 71 in the valleys to around 60 above 4000 feet. East winds up to 20 mph. Chance of rain near 100 percent.

Saturday: Breezy. Occasional showers and slight chance of thunderstorms in the morning, then showers likely in the afternoon. Locally heavy rainfall possible in the morning. Highs 74 to 84 in the valleys to around 66 above 4000 feet. East winds 10 to 20 mph. Chance of rain near 100 percent.

Saturday Night: Mostly cloudy. Breezy. Showers likely in the evening, then occasional showers after midnight. Lows 64 to 71 in the valleys to around 61 above 4000 feet. East winds 10 to 20 mph. Chance of rain 90 percent.

North Kaua’i

Tonight: Showers likely and slight chance of thunderstorms in the evening, then occasional showers and slight chance of thunderstorms after midnight. Locally heavy rainfall possible. Lows 66 to 75. East winds up to 15 mph. Chance of rain near 100 percent.

Saturday: Mostly cloudy. Occasional showers and slight chance of thunderstorms in the morning, then scattered showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 77 to 89. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 90 percent.

Saturday Night: Mostly cloudy with scattered showers. Lows 66 to 73. East winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Tonight: Showers likely and slight chance of thunderstorms in the evening, then occasional showers and slight chance of thunderstorms after midnight. Locally heavy rainfall possible. Lows 66 to 77. Northeast winds 10 to 15 mph. Chance of rain near 100 percent.

Saturday: Occasional showers and slight chance of thunderstorms in the morning, then scattered showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 74 to 86. Northeast winds 10 to 15 mph. Chance of rain near 100 percent.

Saturday Night: Mostly cloudy with showers likely. Lows 66 to 77. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

An upper level low to our west has been aiding in thunderstorm development west of Kauai/Niihau today. As this system weakens and drifts west, a new upper level low will move toward the state from the northeast. A trough will connect these features, helping to maintain relatively unstable conditions, will be draped over the area through the end of next week. Moderate to locally strong trade winds will be unaffected by these upper level features, and are forecast to continue. This combination will continue to bring enhanced showers and a slight chance of thunderstorms to the region this weekend.

Discussion

Radar and satellite show isolated showers across the state this afternoon, with thunderstorms once again remaining well off the coast. There is still a slight chance the western part of the state could see a thunderstorm through tomorrow. Otherwise, expect a continuation of moderate to locally strong trades, and showers focused mainly windward and mauka. An upper level trough will remain over the area for the coming week, keeping conditions slightly more unstable than usual. Within that trough, two separate closed circulations will impact the area's weather. The first is west of the area and moving away. The second will move in from the northeast and should end up centered very close to us by Wednesday. Importantly, the coldest air aloft is not forecast to follow the closed circulation all the way down to a position overhead, but should stay north. This will limit the thunderstorm potential for the middle of next week. Models depict several periods of slightly enhanced moisture moving through, with the first one coming in tonight. We do expect to see a relatively wet period with showers moving quickly within the trade winds from ENE to WSW. This will carry them from windward areas into leeward areas a little more than typically occurs. The next one should arrive Monday night, with another potentially arriving Wednesday. Confidence in the timing of this final one is not high. Finally, trades are forecast to weaken slightly Sunday through Wednesday, but not really enough to boost sea- and land-breeze effects.

Aviation

An upper level low pressure system west of the state continues to create an unstable atmosphere allowing enhanced showers to be embedded within easterly trade winds. These showers are mostly focused over windward and mountain areas, but they can spread into leeward areas as well. MVFR conditions are expected within passing showers, otherwise VFR conditions prevail.
AIRMET SIERRA is not in effect, but could be issued tonight due to potential low clouds and showers causing mountain obscurations.
AIRMET Tango is in effect across the island chain for tempo moderate turbulence between FL300 and FL350. Conditions will continue through the evening but will likely weaken later tonight.
High clouds streaming over Maui and the Big Island are causing light icing conditions in LYR 155-FL210. These conditions are expected to continue through the evening, but chances of light icing should decrease late tonight.

Marine

Moderate to locally strong trades will remain in place over the Hawaiian coastal waters through Saturday. Trade winds will then weaken into the moderate to locally fresh range through early next week. A Small Craft Advisory (SCA) remains in effect over the windier waters and channels surrounding Maui County and the Big Island through Saturday afternoon. An upper low north of Kauai will continue to drift over the northern waters through the weekend keeping a slight chance of thunderstorms in the forecast.
Two moderate, long-period NW and NNW swells moving through the waters will keep surf heights elevated along N and W facing shores through Saturday. Surf along N and W facing shores will slowly trend down on Sunday. A hurricane force low E of Japan will bring another round of moderate, long-period NW (330 deg) swell into the islands towards the middle of next week building surf heights along N and W facing shores. This next long-period swell may possibly reach low-end High Surf Advisory levels Wednesday into Thursday.
A series of small, medium- to long-period S to SW swells will continue to filter into the area through the weekend keeping surf along S facing shores from going flat. Short-period surf along E facing shores increases slightly on Saturday due to the stronger trades, then trends down slightly Sunday through early next week.

Fire weather

Wind speeds and humidity levels will remain below critical fire weather thresholds through the forecast period. Brief heavy rain and isolated thunderstorms are possible through Saturday. Unstable conditions will continue to produce wet weather across the state through next week. Temperature inversion heights near Maui and the Big Island will range from 7,000 to 8,000 feet MSL through Saturday.

HFO Watches/Warnings/Advisories

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

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