West Kaua’i

Tonight: Mostly clear. Isolated light showers in the evening. Lows around 73 near the shore to around 63 above 3000 feet. Light winds. Chance of rain 20 percent.

Monday: Sunny. Isolated showers in the afternoon. Highs 84 to 90 near the shore to around 77 above 3000 feet. Light winds becoming southeast up to 10 mph in the afternoon. Chance of rain 20 percent.

Monday Night: Mostly clear. Lows around 73 near the shore to around 64 above 3000 feet. Northeast winds up to 10 mph in the evening becoming light.

South Kaua’i

Tonight: Partly cloudy with isolated light showers. Lows 69 to 77. Northeast winds around 10 mph. Chance of rain 20 percent.

Monday: Mostly sunny. Scattered showers in the morning, then isolated light showers in the afternoon. Highs 78 to 89. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Monday Night: Partly cloudy. Isolated light showers in the evening, then scattered showers after midnight. Lows 69 to 76. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Kaua’i Mountains

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 65 to 70 in the valleys to around 60 above 4000 feet. Light winds. Chance of rain 50 percent.

Monday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 75 to 83 in the valleys to around 68 above 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Monday Night: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 66 to 71 in the valleys to around 60 above 4000 feet. Light winds becoming east up to 10 mph after midnight. Chance of rain 50 percent.

North Kaua’i

Tonight: Partly cloudy with isolated light showers. Lows 64 to 75. Southeast winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Monday: Mostly sunny with isolated light showers. Highs 72 to 87. East winds up to 15 mph. Chance of rain 20 percent.

Monday Night: Partly cloudy. Isolated light showers in the evening, then scattered showers after midnight. Lows 65 to 75. Southeast winds up to 10 mph. Chance of rain 40 percent.

East Kaua’i

Tonight: Partly cloudy with isolated light showers. Lows 65 to 76. Northeast winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Monday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 78 to 86. Northeast winds up to 15 mph. Chance of rain 50 percent.

Monday Night: Partly cloudy with isolated light showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 66 to 76. Northeast winds up to 10 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Relatively dry and weak trades will gradually strengthen through Wednesday, then become moderate through next weekend. Moisture from the remains of Norbert should arrive Thursday into Friday, greatly increasing shower coverage and intensity. Drier air will move back in next weekend as trades continue.

Discussion

Radar and satellite show isolated showers, mainly over Kauai County. Clouds were building over Big Island, where one or two showers were seen over higher terrain. Winds remain relatively light in most areas, averaging 10 to 15 mph with higher gusts.
An upper level “high over low” block in the to our northeast will keep the upper level pattern rather stable through the coming week. At the surface, a large high pressure system centered near 45N 145W through Wednesday. This will keep us in a trade wind pattern, with wind speeds increasing Wednesday and remaining moderate through next Sunday. Moisture from the remains of Norbert are forecast to move through the area Thursday and Friday, and we have increased PoPs through that period. PW values are still forecast to get up to near 2 inches. Just about the time that moisture arrives, the trades will back slightly and become easterly. A slight turn back to ENE winds looks likely late next weekend. Except for the increased chance of showers Thu/Fri, it should be a relatively dry week for most folks.

Aviation

The forecast remains on track as lighter and drier trade winds hold over the Hawaiian Islands this afternoon. Shower activity should remain limited today thanks to these winds, with the windward side of the islands having a 15-40% chance for showers while the rest of the areas remain dry. The trade winds are generally weak to moderate this afternoon, though winds may become light enough within more wind- protected leeward areas to initiate local topographically- driven breezes. The forecast looks to be close to a rinse and repeat for tomorrow.
For PMDY conditions look to remain dry, though we may get a few low to mid level clouds due to a low sitting north of the region. Opted to keep the forecast dry for the site on Monday, though the ECMWF model shows the potential for some passing showers Monday afternoon. Both the GFS and the ECMWF show showers late Monday into Tuesday, with winds shifting to the north or northwest.
For NSTU, models show passing showers through the TAF cycle, which may bring periods of MVFR cigs and vis.
There is currently one AIRMET in effect for Kauai for mountain obscuration due to clouds around 025, which should end later this evening. No additional AIRMETs are likely, but we'll continue to keep an eye out at reports and webcams should the reach mountain obscuration criteria for clouds and/or precip.

Marine

Moderate trades will continue through the week before gradually strengthening through the latter half of the week. Moisture associated with a weak trough moving in on the trade wind flow may bring a slight uptick in shower activity to the coastal waters Tuesday into Wednesday. While the current forecast has Tropical Storm Norbert dissipating before it nears the Hawaiian coastal waters from the east, remnant moisture from this system is expected to arrive potentially by Thursday, likely bringing more showers.
Surf along south-facing shores will gradually decline through Monday as the small, medium-period energy slowly fades. A series of long-period swells are expected during the second half of the week. The first pulse will gradually fill in Tuesday into Wednesday out of the southwest, followed by larger south-southwest swells Friday into the weekend. Surf could get near advisory thresholds over the weekend, but at this time it looks like it would peak just below advisory thresholds.
Surf along east-facing shores should see an increase during the second half of the week as the trades strengthen and the remnants of Norbert moves through the islands. Flat to tiny surf along north facing shores is expected through the forecast period.

Fire weather

Fire weather risk will remain low the next several days due to light to moderate winds and the effects of recent rainfall. Inversion heights should be 6000 to 7000 ft through Monday. Moisture increases Thu/Fri, and should bring enough showers to keep things relatively wet.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov