West Kaua’i

Rest Of Tonight: Partly cloudy. Breezy. Lows around 74 near the shore to around 65 above 3000 feet. East winds up to 20 mph.

Saturday: Mostly sunny. Breezy. Highs 86 to 93 near the shore to around 77 above 3000 feet. East winds up to 20 mph.

Saturday Night: Partly cloudy. Breezy. Isolated showers in the evening, then scattered showers after midnight. Lows around 74 near the shore to around 63 above 3000 feet. East winds up to 20 mph. Chance of rain 40 percent.

South Kaua’i

Rest Of Tonight: Mostly cloudy. Breezy. Isolated showers early in the evening, then scattered showers after midnight. Lows around 75. Northeast winds 15 to 25 mph. Chance of rain 40 percent.

Saturday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 79 to 89. Northeast winds 20 to 25 mph. Chance of rain 40 percent.

Saturday Night: Breezy. Mostly cloudy with scattered showers. Lows 71 to 78. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Kaua’i Mountains

Rest Of Tonight: Breezy. Cloudy with scattered showers. Lows around 70 in the valleys to around 62 above 4000 feet. East winds 10 to 25 mph with gusts to 45 mph. Chance of rain 50 percent.

Saturday: Breezy. Mostly cloudy with scattered showers. Highs 74 to 81 in the valleys to around 67 above 4000 feet. East winds 10 to 25 mph with gusts to 45 mph. Chance of rain 50 percent.

Saturday Night: Breezy. Mostly cloudy with scattered showers. Lows 65 to 71 in the valleys to around 61 above 4000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

North Kaua’i

Rest Of Tonight: Mostly cloudy with scattered showers. Lows 66 to 76. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 50 percent.

Saturday: Mostly cloudy in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 71 to 88. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Saturday Night: Breezy. Mostly cloudy with scattered showers. Lows 64 to 75. East winds 10 to 20 mph decreasing to up to 15 mph after midnight. Chance of rain 50 percent.

East Kaua’i

Rest Of Tonight: Breezy. Cloudy with scattered showers. Lows 69 to 77. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Saturday: Breezy. Mostly cloudy with scattered showers. Highs 76 to 85. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Saturday Night: Breezy. Mostly cloudy with scattered showers. Lows 67 to 78. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A strong surface high will continue to build north of the state through tonight, bringing windy trade winds through Saturday afternoon. A drier and more stable air mass will also settle in over the state. Trades will ease back to more typical summertime breezy levels Sunday into early next week as the high weakens. Isolated to scattered showers will mainly affect windward locations with dry weather expected for leeward areas. An increase chance of windward clouds and showers may develop by mid- week next week.

Discussion

Satellite and radar imagery show scattered clouds with embedded light showers focusing mainly along windward and mauka slopes. High clouds are moving west to east across the state as the subtropical jet shift over the area. A surface high north of the state has strengthened since this morning, evidenced by a 5 to 6 mb pressure difference between the northern buoys (51001 and 51000) and the southern buoys (51004 and 51002) observations this afternoon. Wind observations have reached advisory level criteria for the windy areas along ridges, through mountainous gaps and downslope mountain areas of Maui County and the Big island. The Big Island Summits and South Kauai have been added to the Wind Advisory through Saturday afternoon as the high is expected to continue to strengthen tonight and hold into Saturday.
Shallow inversion heights have developed over the Big Island with heights around 5500 ft. Precipitable water totals have also dropped .25 inches compared to the morning sounding, indicating drier air is filtering in over the eastern half of the state. This drier and stable airmass will shift over the western half of the state tonight, further limiting showers to windward areas. As the shallow inversion develops over the western half of the state, downslope winds will peak and hold through Saturday afternoon.
The high pressure area will drift eastward on Sunday, loosening local pressure gradients, and easing trades back down to typical summertime levels. Drier conditions should settle in making for lower chances of windward and mauka showers and even drier conditions for leeward area.
Early to mid-next week, trades will further ease as Tropical Storm Genevieve weakens to a post-tropical depression and tracks far northeast of the state, disrupting trade wind flow. Bands of moisture will move over the state, returning typical light to moderate scattered showers to windward and mauka slopes. Both the GFS and ECMWF show a tropical upper level trough shifting just northwest of Kauai by the middle of next week. In addition an area of enhanced moisture may move from east to west across the state. If this comes to fruition, expect a steady increase in low to upper level moisture/clouds and increasing chances moderate to locally heavy windward and mauka showers, especially for the western half of the state.

Aviation

Breezy to windy trade winds will prevail through Saturday night. Occasional MVFR ceilings and visibility in SHRA may accompany showers mainly over the windward and mauka areas.
AIRMET TANGO is in effect for areas over and immediate S through W of all Hawaiian Islands due to windy trade winds and will likely continue through Saturday. No other AIRMETs are currently in effect.

Marine

Windy trade winds are prevailing across the coastal waters this afternoon due to strong surface high pressure north of the state. These windy trades will persist through Saturday as the high strengthens and migrates south towards the islands. As a result, a Small Craft Advisory remains in effect for all nearshore waters. Seas my also exceed 10 feet during this time.
The current south swell will continue to fade through Saturday. This will be followed by the occasional small, medium period pulse of energy out of the southerly quadrant during the next several days.
A small, medium period easterly swell has been observed at nearshore buoys throughout the day. This swell, generated by Tropical Storm Genevieve in the East Pacific, along with increasing wind waves from the strong trades, is resulting in elevated surf along east- facing shores. East shore surf will peak this weekend (likely below advisory criteria) before gradually declining for several days thereafter.
Surf along north facing shores will remain flat to tiny. West facing shores will remain tiny as well, with the exception of those locations exposed to the south swell wrap.

Fire weather

Trades will increase in strength through tonight and hold into Saturday. A drier and more stable airmass has dropped inversion heights to around 5,000 ft, creating gusty downslope winds and low relative humidity values. Precipitation chances will be subdued and limited to windward areas. While the KBDI will remain below the critical thresholds, this hot, dry and windy pattern will create near critical fire weather concerns, especially for areas above the inversion height and downslope of ridges. Trades are expected to return to more normal moderate to locally breezy levels Sunday into early next week. A steady increase in low to upper level moisture also fill in across the state next week.

HFO Watches/Warnings/Advisories

Wind Advisory until 6 PM HST Saturday for Big Island Interior, Big Island North, Big Island South, Big Island Southeast, Big Island Summits, Kahoolawe, Kauai South, Kohala, Koolau Leeward, Lanai Leeward, Lanai Mauka, Lanai Windward, Maui Central Valley North, Maui Central Valley South, Maui Leeward West, Molokai Leeward South, Molokai North, Molokai West, South Haleakala, Waianae Mountains.
Small Craft Advisory until 6 PM HST Saturday for Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters, Big Island Windward Waters, Kaiwi Channel, Kauai Channel, Kauai Leeward Waters, Kauai Northwest Waters, Kauai Windward Waters, Maalaea Bay, Maui County Leeward Waters, Maui County Windward Waters, Oahu Leeward Waters, Oahu Windward Waters, Pailolo Channel.

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Data Courtesy of NOAA.gov