Hilo

Tonight: Cloudy with occasional showers. Locally heavy rainfall possible. Lows 68 to 75 near the shore to around 61 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 90 percent.

Sunday: Mostly cloudy. Occasional showers in the morning, then numerous showers in the afternoon. Locally heavy rainfall possible. Highs 82 to 88 near the shore to 67 to 73 at 4000 feet. East winds up to 10 mph. Chance of rain 90 percent.

Sunday Night: Mostly cloudy with numerous showers. Locally heavy rainfall possible in the evening. Lows 68 to 76 near the shore to around 61 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 70 percent.

Kona

Tonight: Mostly clear. Isolated showers in the evening. Lows 70 to 77 near the shore to 54 to 60 near 5000 feet. Light winds. Chance of rain 20 percent.

Sunday: Sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 87 to 92 near the shore to around 72 near 5000 feet. Light winds. Chance of rain 50 percent.

Sunday Night: Mostly cloudy with scattered showers in the evening, then clear after midnight. Lows 70 to 77 near the shore to around 58 near 5000 feet. Light winds. Chance of rain 40 percent.

Waimea

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows 68 to 75 near the shore to 63 to 69 near 3000 feet. East winds 10 to 20 mph decreasing to up to 20 mph after midnight. Chance of rain 70 percent.

Sunday: Breezy. Partly sunny with scattered showers. Highs 69 to 88. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Sunday Night: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows 68 to 76 near the shore to 63 to 70 near 3000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Kohala

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows 68 to 75 near the shore to 63 to 69 near 3000 feet. East winds 10 to 20 mph decreasing to up to 20 mph after midnight. Chance of rain 70 percent.

Sunday: Breezy. Partly sunny with scattered showers. Highs 69 to 88. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Sunday Night: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows 68 to 76 near the shore to 63 to 70 near 3000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

South Big Island

Tonight: Breezy. Mostly clear with isolated showers. Lows around 78 near the shore to around 60 near 5000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

Sunday: Breezy. Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 89 near the shore to around 73 near 5000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Sunday Night: Partly cloudy. Scattered showers in the evening. Lows around 78 near the shore to around 61 near 5000 feet. East winds 10 to 15 mph. Chance of rain 30 percent.

Puna

Tonight: Cloudy with occasional showers. Locally heavy rainfall possible. Lows 68 to 75 near the shore to around 61 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 90 percent.

Sunday: Mostly cloudy. Occasional showers in the morning, then numerous showers in the afternoon. Locally heavy rainfall possible. Highs 82 to 88 near the shore to 67 to 73 at 4000 feet. East winds up to 10 mph. Chance of rain 90 percent.

Sunday Night: Mostly cloudy with numerous showers. Locally heavy rainfall possible in the evening. Lows 68 to 76 near the shore to around 61 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 70 percent.

Waikoloa

Tonight: Breezy. Mostly clear with scattered showers. Lows around 75 near the shore to around 58 above 4000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Sunday: Mostly sunny. Scattered showers in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 86 to 94 near the shore to 71 to 77 above 4000 feet. Northeast winds up to 10 mph shifting to the northwest in the afternoon. Gusts up to 30 mph. Chance of rain 50 percent.

Sunday Night: Mostly clear. Isolated showers in the evening. Lows 73 to 78 near the shore to around 59 above 4000 feet. Light winds. Chance of rain 20 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