West Kaua’i

Tonight: Mostly clear with isolated showers. Lows around 74 near the shore to around 65 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Sunday: Mostly sunny with isolated showers. Highs 87 to 94 near the shore to around 79 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Sunday Night: Partly cloudy with isolated showers. Lows around 75 near the shore to around 65 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

South Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 72 to 77. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

Sunday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 80 to 91. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Sunday Night: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows around 75. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Mostly cloudy with scattered showers. Lows around 70 in the valleys to around 62 above 4000 feet. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers. Highs 70 to 84. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

Sunday Night: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 68 to 73 in the valleys to around 63 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

North Kaua’i

Tonight: Partly cloudy with scattered showers. Lows 66 to 76. East winds up to 15 mph becoming around 10 mph after midnight. Chance of rain 50 percent.

Sunday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 72 to 89. East winds up to 15 mph. Chance of rain 40 percent.

Sunday Night: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 66 to 76. East winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 69 to 77. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Sunday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 80 to 87. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Sunday Night: Mostly cloudy with scattered showers. Lows 69 to 77. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Breezy trades will focus low clouds and showers over windward and mauka areas through mid-next week. A plume of moisture moving south of the islands will increase rain chances across the eastern end of the state through Monday, followed by drier conditions through midweek. Brewing disturbances within the tropics will need to be monitored for more organized development over the next several days.

Discussion

High pressure to the far northeast and a weak trough approaching from the southeast will continue to drive breezy trades across the state through the weekend. Satellite imagery shows mostly dry conditions persisting across the western half of the state this afternoon along with some passing high cirrus, and increasing low cloud and shower coverage over the eastern end. These clouds and showers moving into windward slopes of the Big Island marks the leading edge of a larger plume of moisture associated with the aforementioned westward-moving surface trough passing south of the state this weekend. Some of this moisture may track up the island chain to increase windward and mauka showers across Maui, Molokai, and possibly Oahu tonight into Sunday, though the highest rain chances remain centered over the Big Island. Forecast soundings indicate modest instability over the Big Island tomorrow. Combined with increasing tropical moisture and daytime heating, this may produce an isolated thunderstorm or two over interior slopes during the afternoon hours.
As the pressure gradient relaxes slightly in response to the surface trough weakening and moving farther westward away from the state, moderate to breezy trades are expected Monday through about Thursday. Drier air will fill in across the island chain midweek, dropping dew points and providing some relief from the mugginess.
Beyond Thursday, forecast confidence decreases, as local weather will depend on the possible development and progression of a tropical cyclone in the Central Pacific. The National Hurricane Center is monitoring an easterly wave about 1,400 miles east- southeast of the state, assigning an 80 percent probability of tropical cyclone development over the next 7 days. While it remains too early to discuss specific local impacts, this feature warrants close monitoring over the coming days.

Aviation

Moderate to fresh trade winds will prevail for the next several days. MVFR ceilings will be focused over typical windward slopes, but will be widespread over windward Big Island tonight due to an area of deeper moisture moving in on the trades. AIRMET Sierra is in effect for windward Big Island and will likely be expanded tonight or Sunday to cover windward Big Island, Maui, and Molokai as the moisture spreads westward. VFR conditions will prevail over most leeward areas, though portions of leeward Big Island could experience extensive MVFR conditions with scattered heavy SHRA Sunday afternoon.
AIRMET Tango is in effect for mod turb downwind of island terrain. This AIRMET will likely be need for next several days.

Marine

Fresh to locally strong trade winds will persist through at least Wednesday as high pressure remains anchored northeast of the state. A Small Craft Advisory remains in effect for the typical windy channels and waters around Maui County and the Big Island through Sunday afternoon. This advisory many need to be extended further, as borderline conditions will prevail through at least Wednesday. Later in the week, the focus will shift to the deep tropics southeast of the state. A tropical cyclone could develop and have an effect on local winds, seas and weather as early as Friday.
Continued small overlapping south-southwest swells will produce south shore surf near August average this weekend and near to above average Monday and Tuesday. A larger swell will arrive Tuesday night and may push surf to the High Surf Advisory level late Wednesday through Friday. This swell should slowly decrease next weekend.
Along east-facing shores, short-period trade wind swell will generate surf just below August average through Thursday. Depending on how potential tropical cyclone development plays out southeast of the islands, an increase in southeast swell is possible Friday and next weekend. Aside from wrapping trade wind energy, surf along north-facing shores will remain flat to tiny through the week.
Due to a combination of peak monthly high tides and water levels running higher than predicted in a few locations, minor coastal flooding will be possible around the afternoon high tide as early as Sunday, with peak conditions Monday through Wednesday.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Sunday for Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters, Maalaea Bay, Pailolo Channel.

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Data Courtesy of NOAA.gov