Photo Credit: Brendan Stephen

West Kaua’i

Today: Occasional showers and chance of thunderstorms in the morning, then numerous showers and chance of thunderstorms in the afternoon. Locally heavy rainfall possible. Highs around 83 near the shore to around 71 above 3000 feet. Southeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain near 100 percent.

Tonight: Mostly cloudy. Showers likely and slight chance of thunderstorms in the evening, then scattered showers and slight chance of thunderstorms after midnight. Locally heavy rainfall possible. Lows around 69 near the shore to around 60 above 3000 feet. Southeast winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 70 percent.

Saturday: Partly sunny with scattered showers. Highs around 84 near the shore to around 73 above 3000 feet. Southeast winds up to 10 mph. Chance of rain 50 percent.

South Kaua’i

Today: Occasional showers and chance of thunderstorms in the morning, then numerous showers and chance of thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 77 to 83. Southeast winds up to 10 mph. Chance of rain near 100 percent.

Tonight: Mostly cloudy. Showers likely and slight chance of thunderstorms in the evening, then showers likely after midnight. Locally heavy rainfall possible in the evening. Lows around 70. Southeast winds up to 10 mph in the evening becoming light. Chance of rain 70 percent.

Saturday: Mostly cloudy with scattered showers. Highs 79 to 85. Southwest winds up to 10 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Occasional showers and chance of thunderstorms. Locally heavy rainfall possible. Highs 73 to 79 in the valleys to around 64 above 4000 feet. South winds up to 15 mph. Chance of rain near 100 percent.

Tonight: Mostly cloudy. Occasional showers and slight chance of thunderstorms in the evening, then showers likely and slight chance of thunderstorms after midnight. Locally heavy rainfall possible. Lows 64 to 69 in the valleys to around 58 above 4000 feet. South winds up to 15 mph. Chance of rain 90 percent.

Saturday: Mostly cloudy with showers likely. Highs 73 to 80 in the valleys to around 64 above 4000 feet. South winds up to 15 mph. Chance of rain 70 percent.

North Kaua’i

Today: Occasional showers and chance of thunderstorms. Locally heavy rainfall possible. Highs 75 to 84. Southeast winds up to 15 mph. Chance of rain near 100 percent.

Tonight: Mostly cloudy. Occasional showers and slight chance of thunderstorms in the evening, then showers likely and slight chance of thunderstorms after midnight. Locally heavy rainfall possible in the evening. Lows 63 to 73. South winds up to 15 mph. Chance of rain 80 percent.

Saturday: Mostly cloudy with showers likely. Highs 75 to 84. South winds up to 15 mph shifting to the north in the afternoon. Chance of rain 70 percent.

East Kaua’i

Today: Occasional showers and chance of thunderstorms. Locally heavy rainfall possible. Highs 71 to 81. South winds up to 15 mph shifting to the southeast in the afternoon. Chance of rain near 100 percent.

Tonight: Mostly cloudy. Showers likely and slight chance of thunderstorms in the evening, then showers likely after midnight. Locally heavy rainfall possible in the evening. Lows 65 to 73. Southwest winds 10 to 15 mph. Chance of rain 70 percent.

Saturday: Mostly cloudy with showers likely. Highs 72 to 83. South winds around 10 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

A strong low pressure system northwest of the state will support a broad band of rain with embedded heavy showers and isolated thunderstorms over and in the vicinity of Kauai today. The band will shift west tonight and Saturday, then move back eastward bringing some more unsettled weather to the islands Saturday night through early next week. Light winds will continue over the smaller islands with only a modest increase in leeward showers anticipated. Conditions should improve and trades should slowly return during the middle to latter part of next week.

Discussion

A deep closed low northwest of the state with a stationary front extending southward through Kauai County, will support a nearly stationary band of heavy showers and thunderstorms over Kauai County today. Considerable cloud cover will blanket the state, with shower coverage decreasing as you move eastward down the island chain. The band of showers and thunderstorms is expected to slowly shift westward tonight and Saturday improving conditions briefly over Kauai County. A digging upper trough will then shift the band of showers and thunderstorms back into Kauai County Saturday night, with the band gradually shifting eastward across the smaller islands through Monday. Periods of heavy rain and thunderstorms will be possible as the band moves back through the state due to plenty of deep layer moisture along with forcing for ascent provided by a strong upper level trough and jet dynamics.
Conditions should improve and trades should slowly return during the middle to latter part of next week.
The Severe Weather threat will linger through mid morning across the waters between Kauai and Niihau, so a Severe Thunderstorm Watch remains in effect for these waters through 10 AM HST this morning. The airmass has been worked over pretty well across Kauai County and the northwest Kauai waters, so the Severe Thunderstorm watch was cancelled here.
A Flood Watch remains in effect for Kauai County through late this afternoon due to the potential for additional flooding in areas which saw a significant amount of rain overnight.
In addition, A Wind Advisory and Winter Weather Advisory is in effect for the Big Island summits through 6 PM HST this evening.

Aviation

Moderate to locally breezy SE winds over the island chain will gradually trend down over the next couple of days. Periods of MVFR cigs/vsbys in SHRA will continue for primarily E and SE facing slopes of the islands. Widespread SHRA/TSRA with IFR/MVFR conds expected for Kauai. Elsewhere, expect limited windward and mauka SHRA with VFR conds expected elsewhere.
AIRMET Sierra remains in effect for mtn obsc over Kauai, Oahu and The Big Island.
AIRMET Tango remains in effect for mod turb btn 090 and FL180.
AIRMET Zulu remains in effect for light icing, as mid- and upper- level clouds continue to stream over the islands from the southwest.

Marine

Thunderstorms capable of producing damaging winds, intense rainfall and waterspouts has developed over the coastal and offshore waters around Kauai and will likely persist through the morning hours. The threat for large areas of heavy rainfall and embedded strong thunderstorms around Kauai is likely to persist through the morning as Special Marine Warnings will likely continue to be issued.
Fresh to locally strong east to southeast winds will ease through the day as the deep low pressure system northwest of the state weakens. A Small Craft Advisory (SCA) has been extended for all waters around Maui County and the Big Island and Oahu Windward waters through today. As this system passes the state far to the north Sunday into early next week, the winds will steadily veer out of the south to southwest and potentially return to the fresh category over the western end of the state by Sunday. Moderate to fresh northerly winds are possible Monday, with a return of a more typical trade wind pattern by midweek as high pressure builds to the north.
Small surf will persist across north facing shores over the next several days with background energy from the northwest and north expected. An upward trend is possible late Sunday as a small long-period north-northwest swell arrives from a system across the far northwest Pacific. This upward trend will continue through the first half of next week as the aforementioned low nearby to the northwest lifts northeastward over the weekend. Heights could reach High Surf advisory levels Monday night through Tuesday night as this swell peaks. Thereafter, expect a gradual downward trend with the swell direction shifting out of the north-northwest by Thursday.
Surf along east facing shores will trend down slightly as locally strong winds trend down over the weekend and veer out of the south. Small surf will persist next week.
Surf along south facing shores remain small with mainly background south-southwest swell expected. The next long-period pulse is expected tonight that should hold through the weekend before moving out. If the moderate to fresh south-southwest winds materialize as advertised later in the weekend, conditions may become rough and choppy along southerly exposures.

HFO Watches/Warnings/Advisories

Flood Watch through this afternoon for Niihau, Kauai,
Wind Advisory until 6 PM HST this evening for Big Island Summits.
Winter Weather Advisory until 6 PM HST this evening for Big Island Summits.
Small Craft Advisory until 6 PM HST this evening for Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov