West Kaua’i

Tonight: Mostly cloudy. Breezy. Isolated showers in the evening, then scattered showers and isolated thunderstorms after midnight. Locally heavy rainfall possible after midnight. Lows around 73 near the shore to around 63 above 3000 feet. East winds up to 20 mph decreasing to up to 10 mph after midnight. Chance of rain 50 percent.

Sunday: Mostly cloudy with scattered showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 86 near the shore to around 75 above 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Sunday Night: Cloudy with isolated showers. Lows around 73 near the shore to around 62 above 3000 feet. East winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

South Kaua’i

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers and isolated thunderstorms after midnight. Locally heavy rainfall possible after midnight. Lows around 74. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Sunday: Mostly cloudy. Numerous showers and isolated thunderstorms in the morning, then scattered showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible in the morning. Highs 79 to 88. East winds 10 to 15 mph. Chance of rain 60 percent.

Sunday Night: Mostly cloudy with scattered showers. Lows around 74. Northeast winds around 10 mph. Chance of rain 40 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Breezy. Showers likely in the evening, then numerous showers and isolated thunderstorms after midnight. Locally heavy rainfall possible after midnight. Lows 64 to 70 in the valleys to around 60 above 4000 feet. East winds 10 to 25 mph decreasing to 10 to 15 mph after midnight. Chance of rain 70 percent.

Sunday: Mostly cloudy. Numerous showers and isolated thunderstorms in the morning, then scattered showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 74 to 82 in the valleys to around 65 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Sunday Night: Cloudy with scattered showers. Lows 64 to 71 in the valleys to around 60 above 4000 feet. East winds around 10 mph. Chance of rain 40 percent.

North Kaua’i

Tonight: Mostly cloudy. Scattered showers in the evening, then scattered showers and isolated thunderstorms after midnight. Locally heavy rainfall possible after midnight. Lows 66 to 74. East winds up to 15 mph. Chance of rain 50 percent.

Sunday: Mostly cloudy with scattered showers and isolated thunderstorms. Locally heavy rainfall possible in the morning. Highs 76 to 86. East winds up to 15 mph. Chance of rain 50 percent.

Sunday Night: Cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 66 to 74. East winds up to 10 mph. Chance of rain 30 percent.

East Kaua’i

Tonight: Mostly cloudy. Showers likely in the evening, then numerous showers and isolated thunderstorms after midnight. Locally heavy rainfall possible after midnight. Lows 66 to 77. East winds 10 to 15 mph. Chance of rain 70 percent.

Sunday: Cloudy. Numerous showers and isolated thunderstorms in the morning, then scattered showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 72 to 85. East winds 10 to 15 mph. Chance of rain 70 percent.

Sunday Night: Cloudy with scattered showers. Lows 65 to 77. East winds around 10 mph. Chance of rain 40 percent.

Detailed Forecast

Synopsis

Trades will continue for the coming week, but with weaker winds than we have had the past couple days. Two upper-level lows will be close enough to bring enough instability for isolated thunderstorms, mainly over western areas, through Wednesday. Low- level humidity will increase, ending our recent enhanced fire threat.

Discussion

This afternoon, isolated showers continue over the area, mostly on the windward side of the Big Island and over Kauai. Other showers were seen over the coastal waters, mainly between the Big Island and Maui. A large area of showers, embedded within an even larger area of high clouds, was moving north toward the Big Island and may reach eastern Maui County later this evening. A Red Flag Warning continues through the afternoon for leeward Oahu and Kauai, and all of Niihau (see zone details below). A Winter Weather Advisory continues through 6 AM MST for the Big Island Summits.
A closed upper level low centered about 300 miles to our southwest will drift NW through Monday afternoon before weakening to a trough. This trough will then move slowly east over the state, and then become nearly stationary, through Tuesday. This trough will have cold air aloft, resulting in enough instability for a slight chance of thunderstorms. The best chance will be over the western part of the state. Models are in fairly good agreement that the trough will evolve back into a closed low much farther off to the southwest late Wednesday, and drift west for several days. Another closed low is expected to form to our east late next week.
At the surface, a series of high pressure centers to our north will move from west to east, keeping us in trade winds. Moisture below the inversion will be high today, but is forecast to decrease to more normal levels the remainder of the week. Therefore, rather typical windward showers are to be expected, with a few making it over to the leeward side with light rain amounts.

Aviation

Breezy trade wind conditions will continue decreasing into tomorrow. Isolated to scattered showers are possible overnight tonight over most of the state as the upper level low continues to pull tropical moisture northward. This shower activity could cause temporary decreases in visibility, lower ceilings and MVFR conditions with the greatest chances of longer-lasting conditions over the Big Island.
Light icing conditions continue over mainly the western side of the state, including Maui and Big Island, where freezing levels in the 00z Hilo sounding are 15kft. These conditions will continue over the next 12-24 hours so will continue the mention of icing which may also expand over the whole state.
Will also continue AIRMET Tango for moderate low level turbulence below 9kft. These conditions will continue over the night but winds will decrease over the next 12-24 hours.
AIRMET Tango also remains in effect for upper level turbulence over most of the state, but with a weakening trend forecast tonight.
AIRMET Sierra continues for mountain obscuration mainly for Kauai and Big Island, but could be expanded for windward areas overnight as lower cloud decks are possible with increasing moisture lasting into the morning hours.

Marine

Trade winds will gradually decline over the next couple of days as a surface high centered roughly 450 nm north of Hawaii moves eastward and slowly weakens. Trade winds peaked yesterday, but held at fresh to strong levels through much of the day. With the high weakening and local pressure gradient relaxing, the Small Craft Advisory (SCA) has been scaled back to cover the typically windy waters around the Big Island and Maui as well as Maui County windward waters and the Kaiwi Channel through tonight. The SCA will likely be reduced to the typically windy waters on Sunday and should be dropped completely by Monday as winds ease to gentle to locally fresh strength. There is some difference in the guidance heading into midweek, bringing the possibility of some increase in winds Tuesday night or Wednesday.
The last two in a series of north-northwest swells are expected during the next few days. A moderate north-northwest (340 degree) swell peaked at around 5 ft 13 seconds at the PacIOOS Waimea Bay buoy this morning and will slowly decline tonight and Sunday. A smaller north-northwest (330-340 degrees) swell may push surf along north and west facing shores back near seasonal average on Monday, then decline Tuesday. As this swell fades on Wednesday, a moderate short-period north swell will produce a brief boost in north shore surf. Since the storm generating the swell will be compact and fast-moving, there is some uncertainty as to the potential surf height, though it appears that near seasonal average is likely at this time.
Rough surf along east facing shores will slowly decrease Sunday into early next week as trades ease. PacIOOS buoys off windward shores show the trade wind energy at 8 ft at 8 seconds, which supports east shore surf below the High Surf Advisory level this afternoon. Expect surf along east facing shores to begin to decline late tonight, fall to around seasonal average on Sunday, then drop slightly on Monday and Tuesday. While wind wave energy is not expected to change much midweek, the above mentioned north swell could increase surf along some exposed eastern shores.
South facing shores will experience mainly small background swell through the week.

Fire weather

The Red Flag Warning continues for Niihau, and leeward areas of Kauai and Oahu through this afternoon. Trade winds across the state remain breezy today, but will gradually decrease tonight to light to moderate speeds for the remainder of the week. Increased humidity values and decreasing winds will help maintain below critical fire weather thresholds tonight into next week. Temperature inversion heights near Maui and the Big Island will range from 7,500 to 8,500 feet elevation today.

HFO Watches/Warnings/Advisories

Red Flag Warning until 6 PM HST this evening for Niihau, Kauai South, Kauai Southwest, East Honolulu, Honolulu Metro, Ewa Plain, Waianae Coast, Oahu North Shore, Central Oahu, Waianae Mountains.
Winter Weather Advisory until 6 AM HST Sunday for Big Island Summits.
Small Craft Advisory until 6 AM HST Sunday for Kaiwi Channel, Maui County Windward Waters.
Small Craft Advisory until 6 PM HST Sunday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.