West Kaua’i

Tonight: Haze in the evening. Mostly cloudy with isolated showers. Lows 67 to 72 near the shore to around 58 above 3000 feet. Light winds. Chance of rain 20 percent.

Monday: Mostly cloudy with scattered showers. Highs around 84 near the shore to around 71 above 3000 feet. Light winds becoming south up to 10 mph in the afternoon. Chance of rain 40 percent.

Monday Night: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 67 to 72 near the shore to around 58 above 3000 feet. Light winds. Chance of rain 20 percent.

South Kaua’i

Tonight: Haze in the evening. Mostly cloudy with isolated showers. Lows around 69. Light winds. Chance of rain 20 percent.

Monday: Mostly cloudy with isolated showers. Haze in the afternoon. Highs 77 to 85. Light winds. Chance of rain 20 percent.

Monday Night: Mostly cloudy with isolated showers. Lows around 69. Light winds. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 62 to 68 in the valleys to around 56 above 4000 feet. Light winds becoming southeast up to 10 mph after midnight. Chance of rain 40 percent.

Monday: Mostly cloudy with scattered showers. Haze in the afternoon. Highs 72 to 82 in the valleys to around 64 above 4000 feet. Southeast winds up to 10 mph in the morning becoming light. Chance of rain 50 percent.

Monday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 62 to 68 in the valleys to around 55 above 4000 feet. Southeast winds up to 10 mph. Chance of rain 30 percent.

North Kaua’i

Tonight: Mostly cloudy with isolated showers. Lows 62 to 70. Light winds. Chance of rain 20 percent.

Monday: Partly sunny with isolated showers. Highs 76 to 83. Light winds. Chance of rain 20 percent.

Monday Night: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows 62 to 71. Light winds. Chance of rain 20 percent.

East Kaua’i

Tonight: Mostly cloudy with isolated showers. Lows 63 to 74. Light winds. Chance of rain 20 percent.

Monday: Mostly cloudy with isolated showers. Haze in the afternoon. Highs 72 to 83. Light winds. Chance of rain 20 percent.

Monday Night: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 63 to 73. Light winds. Chance of rain 20 percent.

Detailed Forecast

Synopsis

A trough northwest of Kauai will maintain a ridge over the islands resulting in minimal shower activity and light southeasterly winds. Another front will approach and stall northwest of Kauai on Tuesday, bringing clouds and showers to the western end of the island chain Wednesday. More typical trade wind weather with showers favoring windward and mountain areas will become reestablished Thursday into the weekend.

Discussion

The forecast has been updated to reflect the latest National Blend of Models (NBM), but the changes are minimal. There remains good agreement with the models in the short term, but significant differences in the ECMWF and GFS global models Wednesday onwards.
A surface and upper level ridge over the islands is maintaining light southeasterly flow with a stable airmass in place. This results is localized land and sea breezes and minimal shower activity. The surface ridge has been pushed over the islands due to a trough to the northwest which is expected to weaken and be pushed to the northeast by another front currently far to the northwest of the main Hawaiian islands.
The GFS and ECMWF are in good agreement with this next front approaching from the northwest Tuesday. Both models bring pre- frontal convergence bands to the northwest of Kauai Tuesday night. The GFS stalls the front to the northwest of Kauai, while the ECMWF brings the front over the Garden Isle, with additional moisture being drawn northward over the Oahu and parts of Maui County. For now the forecasts falls more in line with the GFS in keeping the bulk of the shower activity west of Kauai.
The global models have some significant differences during the second half of the week. Both models show the front dying and being replaced by a surface trough. The GFS goes on to form a low pressure system along the trough, west of the islands, with the low moving to the west. The GFS also develops a strong upper level low in conjunction with the surface feature. The ECMWF is slower to develop a low along the trough, and when it does so, it develops one north of the islands that lifts northward. While the models show significant differences during the second half of the week, they remain in decent agreement with a ridge north of the islands allowing trade winds to build back in over the islands. Accompanying the trades would be showers focused over the windward and mountains areas.
The upper level feature from the GFS could spell increased winds over the Big Island Summits Thursday on through the weekend. Currently the forecast keeps winds below advisory levels for the summits, however will have to watch future model runs to see how things may play out.

Aviation

Light southeasterly flow will continue through the forecast period with local sea breezes during the day and land breezes at night. VFR conditions expected through Monday under a relatively dry and stable air mass.
No AIRMETs are in effect and none are expected.

Marine

Ridging will remain in place over the area for the first half of the week, maintaining light to moderate southeast background winds. This pattern will allow for daytime sea breezes and nighttime land breezes along waters adjacent to the coasts. Meanwhile, an extra large northwest swell that peaked Sunday morning will decline over the next day or so, but will produce seas above Small Craft Advisory (SCA) levels for exposed waters through midday on Monday. A Small Craft Advisory remains in effect until that time, but seas will quickly fall below SCA levels Monday afternoon into Monday night as the swell continues to fade. On Wednesday, a front will approach Kauai from the northwest, but guidance continues to indicate that it will weaken and then retreat back to the west during the latter part of the week. Easterly trade winds will finally return Friday into the weekend as surface high pressure builds northeast of the area.
The current, extra-large, long-period northwest (310-320 degree) swell peaked earlier Sunday and will slowly decline tonight through Monday. With that said, as of Sunday afternoon the Waimea Bay buoy 51201 continues to report impressive northwest swell energy at 12-15 feet, 17 seconds. This swell is expected to slowly lose energy tonight, but it will continue to produce warning level surf throughout the night and into early Monday. Therefore, the High Surf Warning remains in effect through noon on Monday for exposed north and west facing shores of most islands. Surf is then expected to drop to advisory levels by Monday afternoon as the swell energy eases. Another large, long period northwest swell (310-330 degree) is forecast to fill in on Wednesday, peak Thursday, then slowly subside on Friday. Surf may once again approach warning levels.
East shore surf will remain small through the weekend due to weak winds. Some south facing shores experienced a small amount of westerly wrap from this weekend's large northwest swell on Sunday, but this will ease by Monday and south shore surf will remain small throughout the next few days.

Fire weather

Rather dry conditions are expected to persist through Tuesday. Winds will be light and variable under a stable land and sea breeze pattern, preventing critical fire weather thresholds from being approached. With the inversion holding around 6,500 ft, very dry conditions will persist on the upper elevations of the Big Island and Maui.

HFO Watches/Warnings/Advisories

High Surf Warning until noon HST Monday for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Maui Windward West, Kona, Kohala, Kauai North, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala.
Small Craft Advisory until noon HST Monday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Alenuihaha Channel, Big Island Windward Waters.

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