West Kaua’i

Tonight: Partly cloudy with isolated showers. Lows 70 to 75 near the shore to around 62 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Friday: Breezy. Mostly sunny with isolated showers. Highs 85 to 90 near the shore to around 76 above 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Friday Night: Breezy. Partly cloudy with isolated showers. Lows 69 to 74 near the shore to around 61 above 3000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

South Kaua’i

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

Friday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 81 to 89. Northeast winds 15 to 25 mph. Chance of rain 40 percent.

Friday Night: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Scattered showers. Lows around 73. Northeast winds 15 to 25 mph. Chance of rain 40 percent.

Kaua’i Mountains

Tonight: Breezy. Mostly cloudy with numerous showers. Lows 64 to 70 in the valleys to around 59 above 4000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Friday: Breezy. Partly sunny with scattered showers. Highs 74 to 83 in the valleys to around 66 above 4000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Friday Night: Breezy. Mostly cloudy with scattered showers. Lows 64 to 69 in the valleys to around 59 above 4000 feet. East winds up to 20 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 66 to 74. Southeast winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 50 percent.

Friday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 76 to 87. East winds up to 20 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 64 to 74. East winds 10 to 15 mph. Chance of rain 40 percent.

East Kaua’i

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 65 to 77. Northeast winds up to 15 mph. Chance of rain 70 percent.

Friday: Breezy. Partly sunny with scattered showers. Highs 74 to 86. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers. Lows 64 to 76. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Moderate trade winds and stable conditions will limit showers across the area through Saturday morning. A front and upper low will approach and bring unsettled weather across the state, particularly Kauai Sunday and Sunday night. Remnant moisture will continue to push over the state Monday and Tuesday.

Discussion

A 1025 mb surface high far northeast of the state is driving moderate trade winds across Hawaii today. Visible satellite and radar shows isolated showers moving across windward waters with mostly sunny leeward sides aside from the sea breeze driven clouds over the Big Island Kona slopes. Weak troughing aloft over the state is not strong enough to erode the trade wind inversion. Little change is expected in the forecast through Saturday morning with stable, moderate trades carrying in occasional windward and mauka clouds and showers.
A cold front 900 miles north of Hawaii will slowly approach over the next several days. The front is forecast to weaken through Saturday before an upper low cuts off out of the North Central Pacific and quickly moves towards the state passing just northwest of Kauai on Sunday before moving away to the west. 500 mb temperatures will cool to around -10 C over Kauai to around -8 C near the Big Island as the low passes by.
The upper low will induce a trough at the surface directly over the islands on Sunday. Winds will weaken slightly and shift out of the southeast around Big Island and Maui County and out of the northeast for Kauai and Oahu. Clouds and showers will increase as early as Saturday afternoon for the Big Island, and statewide Saturday night into Monday, as frontal moisture moves in over Kauai and Oahu. Winds will shift back to trades as the trough moves west of the state Sunday night and Monday following the upper low. Trades will push clouds and showers in place over the state Monday keeping conditions quite wet. Main heavy rain potential lies in the brief passage of the upper low over the low level frontal moisture, which coincides across the far western end of the state Sunday and Sunday night. Considering a Flood Watch for Kauai during the Sunday to Sunday night time period, with particular emphasis on the north and east sides of the island.
In the long-range, additional uncertainty is portrayed by the GFS, depicting a weak, cutoff developing just west of the island chain midweek. Should this feature become fruitful, it would result in an increase of showers moving back in from the west. However, acknowledging this event is still several days out, it is simply worth noting so it can be monitored going forward as new guidance becomes available.

Aviation

Moderate trade winds will persist into Saturday as a surface ridge holds north of the islands. Moisture moving along the trade wind flow will produce periods of MVFR conditions along windward slopes, mainly at night, as well as across the Kona slopes of the Big Island each afternoon. VFR will prevail elsewhere.
A sharp upper-level trough will drift down the island chain through Friday. AIRMET Tango for TEMPO moderate turbulence is currently in place for Kauai and Oahu between FL220 and FL360. The AIRMET will likely be expanded to Maui for tonight and may continue into the day on Friday with some adjustments for flight level.

Marine

High pressure far northeast of the Hawaiian Islands will maintain moderate to locally breezy trades through tomorrow, decreasing on Saturday. A cold front is forecast to approach the western waters Sunday into Monday with current model runs showing the front stalling just northwest of Kauai. Strong (potentially gale force) northeast trade winds can be expected northwest of the front, while lighter east to northeasterly winds can be expected east of the front. Scattered thunderstorms will be possible along the front due to strong upper level support. Moderate east northeast trades are then possible for the first half of next week.
A small, long period NNW swell (330) will fill in tonight and and keep surf along N and W shores slightly elevated through Friday. Surf will then trend upward late Friday through Monday in response to NNW and NNE swells. Forerunners from a moderate, long period NNW (330) swell will arrive Friday evening with surf peaking around High Surf Advisory (HSA) levels Saturday morning and holding through Saturday night. The surf forecast then becomes more challenging by Sunday as larger short period NNE swell fills in from the approaching front and mixes with the mid- longer period NW swell from Saturday. Surf will likely be rough and jumbled due to the close proximity of the fetch sending the NNE swell. The NNE swell looks to send the largest surf to the western end of the state, where N and E facing shores of Kauai and Oahu could potentially see HSA surf by Sunday afternoon. As things stand currently, HSA conditions are likely Saturday for N and W facing shores of all islands. HSA conditions are then again possible for N and E facing shores of the western islands by Sunday afternoon. Stay tuned on this swell as uncertainty remains with the evolution of the front. A moderate to large swell is then possible around the middle of next week.
Surf along E shores will remain small to moderate through Saturday. Strengthening post-frontal NNE winds may bring a rapid increase in wind waves and short period fresh swell for N and E shores Sunday through early next week, particularly over the western end of the state. A small south swell will slowly fade today through this weekend.

Fire weather

Increased relative humidity values and moderate trades will keep fire weather conditions below critical thresholds for the next several days. Temperature inversion heights near Maui and the Big Island will range from 6500 to 7500 feet elevation into tonight.

HFO Watches/Warnings/Advisories

None.

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