West Kaua’i

Rest Of Tonight: Breezy. Partly cloudy with isolated showers. Lows 70 to 75 near the shore to around 61 above 3000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

Saturday: Breezy. Mostly sunny with isolated showers. Highs around 88 near the shore to around 76 above 3000 feet. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 20 percent.

Saturday Night: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 73 near the shore to around 62 above 3000 feet. East winds 10 to 15 mph. Chance of rain 40 percent.

South Kaua’i

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

Saturday: Breezy. Partly sunny with scattered showers. Highs 81 to 89. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Saturday Night: Mostly cloudy with scattered showers. Lows around 73. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Rest Of Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 64 to 70 in the valleys to around 59 above 4000 feet. East winds 10 to 25 mph decreasing to up to 25 mph after midnight. Chance of rain 70 percent.

Saturday: Breezy. Partly sunny with scattered showers. Highs 73 to 83 in the valleys to around 65 above 4000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Saturday Night: Breezy. Mostly cloudy with scattered showers. Lows 64 to 70 in the valleys to around 60 above 4000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

North Kaua’i

Rest Of Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 65 to 74. East winds 10 to 20 mph decreasing to up to 15 mph after midnight. Chance of rain 60 percent.

Saturday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 77 to 88. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

Saturday Night: Mostly cloudy with scattered showers. Lows 66 to 74. East winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Rest Of Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 65 to 77. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Saturday: Breezy. Mostly cloudy with scattered showers. Highs 74 to 86. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Saturday Night: Mostly cloudy with scattered showers. Lows 65 to 77. East winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Update

Current observations for the Summits of Mauna Kea and Mauna Loa show winds exceeding advisory level, thus have opted to add a Wind Advisory accordingly through 16z (6 AM HST). Will follow up for the morning package as needed.

Synopsis

This evening and tonight, enhanced showers and isolated thunderstorms will be possible across windward portions of the Big Island and the eastern coastal waters. Windy trades will continue through the night, and a Wind Advisory remains in effect for the typically windy places of Maui County and the Big Island. An upper level low drifting from east to west across the state will pull deeper tropical moisture over the islands, increasing humidity and shower trends and finally bringing an end to fire weather concerns by Saturday evening. Trade winds will decrease throughout the weekend, dropping back to moderate levels through much of next week.

Aviation

Strong trades winds continue into Saturday. VFR conditions prevail across the state through the early evening with incoming clouds and showers to impact Big Island and Maui County tonight.
AIRMET Sierra for tempo mountain obscurations above 2500 feet will go into effect at 08Z tonight for windward and southeast sides of the Big Island. Lower ceilings and visibility may reach windward Maui later tonight. VFR conditions should prevail elsewhere. Brief windward mountain obscurations may occur elsewhere overnight with incoming showers.
AIRMET Tango is in effect for tempo moderate turbulence below 9000 feet for all leeward areas, and from FL250 to FL350 for the whole state. AIRMET Tango is also in effect for sustained surface winds of 30 knots or greater across the Big Island, Maui and Lanai.

Marine

Strong trades will approach low-end gales as strong high pressure establishes N of the Hawaiian Islands. The strongest winds are expected today through the first of Saturday. Trades then gradually weaken through the weekend before perking up during the early to middle portion of next week.
Energy shifting toward the shorter period bands at the Waimea Bay PacIOOS buoy this afternoon indicates the gradual departure of the current NNW (330) swell. Moderate surf along N and W facing shores has therefore likely reached its minimum along N and W facing shores for the time being. Longer period energy associated with a NNW (330-340) swell has registered on offshore NDBC buoys 51101 and 51001 this afternoon, and surf will be on the rise tonight peaking near the High Surf Advisory (HSA) threshold. This short- lived swell then fades Saturday into early next week.
E facing shores experience short period fresh swell and plenty of wind wave action courtesy of ongoing strong trades. Surf will trend downward beginning late Saturday as trades gradually weaken. South facing shores see small background swell through the week.

Fire weather

Windy trades will continue into Saturday, along with drier humidity levels ahead of a surge of enhanced moisture that will arrive during the day. Confidence in reaching Red Flag Warning criteria on Saturday is lower than it was for today, as it will largely depend on how quickly an upper low moving over the islands begins to increase humidity levels statewide. Regardless, at this time confidence was not high enough to warrant cancelling the Red Flag Warning for Saturday, as it is possible that at least leeward areas of the western islands could maintain dry conditions well into Saturday afternoon. Winds will generally begin to decrease on Saturday, though they will still remain above critical fire weather thresholds. Therefore, the Red Flag Warning remains in effect through Saturday afternoon. Beyond that, a significant increase in moisture and a decrease in trade wind speeds will mitigate fire weather concerns through the rest of the weekend and into next week.

Prev discussion

An interesting and somewhat complex weather pattern is expected over the next 48 hours, with multiple different weather hazards in effect for various parts of the state.
An area of surface high pressure centered along 30N far north of the island chain is expected to slightly strengthen as it continues to slide eastward this evening. Locally, this has translated into a windy trade wind day, with observations across many of the typically windy locations of Maui County and the Big Island showing sustained wind speeds in excess of 30 mph and/or gusts over 50 mph. A Wind Advisory remains in effect for Kahoolawe, most of Lanai, West and Central Maui including South Haleakala, and the Big Island including the Kohala and Kau Districts as well as the Humuula Saddle area through tonight. On Saturday, the high to our north will be located farther east, and it is also expected to weaken a bit compared to today and tonight. As a result, trade wind speeds across the island chain will remain gusty on Saturday, but will also gradually decline throughout the day.
In addition to the gusty winds, efficient mixing of dry air aloft down to the surface within a stable airmass over the islands has created fire weather concerns across all leeward areas, as well as central and interior sections of some islands, over the past couple of days. Surface observations show that Red Flag Warning criteria was met this afternoon with relative humidity values dropping into the low 40 percent range. The Red Flag Warning that is currently in effect has been allowed to continue for one more day. With that being said, latest model guidance suggests that enhanced moisture will begin moving into the eastern end of the state this evening into Saturday. However, it remains possible that drier air could linger over at least some islands into early Saturday afternoon, corresponding with maximum daytime heating and winds that remain above critical fire weather thresholds. With uncertainty still surrounding the timing of increased humidity levels over the islands, the Red Flag Warning remains unchanged for now, but interests should continue to monitor for any future updates that may be necessary. See the Fire Weather section below for more details.
Meanwhile, this evening through tonight, a mid- to upper-level low will move westward over the Big Island, and will be located just west of the state around sunrise Saturday morning. Latest regional satellite imagery shows clouds upstream of the Big Island in the vicinity of the upper low at this time are beginning to become more robust as they approach the eastern Hawaiian coastal waters. As this cluster of clouds approaches windward areas of the Big Island this evening, it could produce some enhanced showers as it interacts with the Big Island terrain and the low aloft moves overhead. Further destabilization is expected, as 500mb temperatures drop into the -10C to -13C range. Therefore, isolated thunderstorms have been included in the forecast for the Big Island and the eastern coastal waters throughout the night, as southerly flow begins to draw moisture northward and precipitable water values begin to increase. The latest HREF rainfall rate probabilities are also hinting that some showers or thunderstorms this evening into tonight could produce rainfall rates in excess of 0.5 inch per hour along windward Big Island. Heavy rain has also been introduced into the forecast, corresponding to the areas of isolated thunder chances. Of note, although the threat for flash flooding across windward Big Island this evening is very low, it is non-zero. With this afternoon's forecast updates, chances for snow and/or freezing rain have also been introduced for the Big Island summits, and a Winter Weather Advisory has been issued to account for potential snow and ice accumulations for the summits through the next couple of days.
On Saturday, southerly winds aloft along the east side of the upper low will pull additional moisture across the eastern islands from the deep tropics, likely creating an abrupt end to fire weather concerns at some point on Saturday. Humidity levels and instability will increase across the state with this passing upper low, resulting in continued enhanced showers and isolated thunderstorms over the eastern end of the island chain, as well as the western edge of the coastal waters.
Trade wind speeds continue to weaken into the light to moderate range from Sunday night through much of next week as the ridge north of the islands weakens in response to a passing cold frontal system farther to the north. More stable conditions move back into the islands with brief passing showers favoring windward and mountain areas during the overnight to early morning hours through Tuesday. By Wednesday another upper low will move over the western islands enhancing overnight to early morning shower coverage statewide through the end of next week.

HFO Watches/Warnings/Advisories

Red Flag Warning until 6 PM HST Saturday for Niihau, Kauai South, Kauai Southwest, East Honolulu, Honolulu Metro, Ewa Plain, Waianae Coast, Oahu North Shore, Central Oahu, Waianae Mountains, Molokai North, Molokai West, Molokai Leeward South, Lanai Windward, Lanai Leeward, Lanai South, Lanai Mauka, Kahoolawe, Maui Leeward West, Maui Central Valley North, Maui Central Valley South, South Maui/Upcountry, South Haleakala, Big Island South, Big Island Southeast, Big Island North, Kohala, Big Island Interior.
Wind Advisory until 6 AM HST Saturday for Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Kohala, Big Island Interior, Big Island Summits, Lanai Windward, Lanai Leeward, Maui Central Valley North, Maui Central Valley South, South Haleakala, Big Island Southeast, Big Island North.
Winter Weather Advisory until 6 AM HST Sunday for Big Island Summits.
Small Craft Advisory until 6 PM HST Saturday for all Hawaiian waters,

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