Photo Credit: James Grenz

Hilo

Today: Mostly cloudy. Frequent showers and slight chance of thunderstorms in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 79 to 84 near the shore to 64 to 70 at 4000 feet. South winds up to 10 mph shifting to the east in the afternoon. Chance of rain 80 percent.

Tonight: Cloudy with frequent showers. Lows 65 to 71 near the shore to around 58 at 4000 feet. West winds up to 10 mph. Chance of rain 90 percent.

Friday: Mostly cloudy with numerous showers. Highs 79 to 85 near the shore to 64 to 70 at 4000 feet. Northwest winds up to 10 mph shifting to the east in the afternoon. Gusts up to 30 mph. Chance of rain 70 percent.

Kona

Today: Sunny with slight chance of thunderstorms and isolated showers in the morning, then mostly cloudy with scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 83 to 90 near the shore to around 70 near 5000 feet. Northwest winds up to 10 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Lows 71 to 76 near the shore to 51 to 57 near 5000 feet. Light winds. Chance of rain 20 percent.

Friday: Partly sunny in the morning, then cloudy with scattered showers in the afternoon. Highs 83 to 89 near the shore to around 70 near 5000 feet. Light winds becoming northwest up to 10 mph in the afternoon. Chance of rain 50 percent.

Waimea

Today: Mostly cloudy. Numerous showers and slight chance of thunderstorms in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 66 to 87. East winds up to 15 mph. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 65 to 72 near the shore to 56 to 64 near 3000 feet. Southeast winds up to 20 mph. Chance of rain 50 percent.

Friday: Breezy. Mostly cloudy with scattered showers. Highs 67 to 87. East winds up to 25 mph. Chance of rain 50 percent.

Kohala

Today: Mostly cloudy. Numerous showers and slight chance of thunderstorms in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 66 to 87. East winds up to 15 mph. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 65 to 72 near the shore to 56 to 64 near 3000 feet. Southeast winds up to 20 mph. Chance of rain 50 percent.

Friday: Breezy. Mostly cloudy with scattered showers. Highs 67 to 87. East winds up to 25 mph. Chance of rain 50 percent.

South Big Island

Today: Mostly cloudy. Breezy. Numerous showers and slight chance of thunderstorms in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible. Highs around 85 near the shore to around 68 near 5000 feet. East winds 10 to 25 mph. Chance of rain 60 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 71 to 76 near the shore to around 53 near 5000 feet. Northeast winds 10 to 25 mph. Chance of rain 50 percent.

Friday: Breezy. Mostly cloudy with scattered showers. Highs around 84 near the shore to around 68 near 5000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Puna

Today: Mostly cloudy. Frequent showers and slight chance of thunderstorms in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 79 to 84 near the shore to 64 to 70 at 4000 feet. South winds up to 10 mph shifting to the east in the afternoon. Chance of rain 80 percent.

Tonight: Cloudy with frequent showers. Lows 65 to 71 near the shore to around 58 at 4000 feet. West winds up to 10 mph. Chance of rain 90 percent.

Friday: Mostly cloudy with numerous showers. Highs 79 to 85 near the shore to 64 to 70 at 4000 feet. Northwest winds up to 10 mph shifting to the east in the afternoon. Gusts up to 30 mph. Chance of rain 70 percent.

Waikoloa

Today: Sunny with scattered showers in the morning, then mostly cloudy with scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 82 to 90 near the shore to 67 to 72 above 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers. Lows around 75 near the shore to 52 to 58 above 4000 feet. Southeast winds up to 15 mph. Chance of rain 20 percent.

Friday: Mostly cloudy. Isolated showers in the morning, then scattered showers in the afternoon. Highs 83 to 89 near the shore to 67 to 73 above 4000 feet. Northeast winds up to 10 mph shifting to the northwest in the afternoon. Gusts up to 35 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Breezy east southeast winds will continue through the weekend, with downstream blocking of the winds occurring at times by the Big Island and Maui. The bulk of shower activity will focus over windward and southeast facing slopes of the Big Island and Maui, through incoming showers could impact any island the next several days. An upper low northeast of the Big Island could provide some shower enhancement through tonight. Winds will back to the trade wind direction by Sunday.

Discussion

A nearly stationary 1035 mb surface high is centered far northeast of Hawaii while a slow moving cold front is located to the west near the International Dateline. The high is driving fresh to strong trade winds upstream, but veer slightly east southeast over the state. Meanwhile, a weak upper low is about 200 miles north of the state which is creating some instability across the state and will act to enhance cloud heights and showers today and tonight.
Radar and infrared satellite shows low clouds with numerous moderate to heavy showers windward and southeast portions/waters of the Big Island and Maui. Scattered showers persist across the other islands. Expect this trend to continue through the morning, with leeward sides of Maui and the Big Island seeing more showers by afternoon. A slight chance of thunderstorms has also been added to the forecast for the Big Island today.
The east-southeast flow and terrain effects will greatly influence wind speed and shower coverage across the state through the weekend as the front slowly approaches. Blockage from the Big Island will somewhat dampen the strong winds across the smaller islands, resulting in some windward/northern shores being breezy while other, mostly leeward areas, seeing moderate or even gentle winds at times over the next several days. The bulk of rainfall is likely to occur over exposed windward and southeast facing slopes of the Big Island and Maui through Saturday. The rest of the state will be in the shadow of both islands, which is likely to reduce the overall amount of rainfall expected. That said, showers could just slide over one of the other islands with a slight shift in wind direction. By Sunday, the front to the west will stall and begin to weaken while winds across the state return to a more easterly direction into early next week.

Aviation

High pressure far NE of the islands will produce moderate to locally breezy E to ESE trade winds into Friday. A broad trough aloft just N of the islands is destabilizing the atmosphere, and overnight soundings indicate a moist and unstable profile capable of supporting heavy showers, and quite possibly a thunderstorm. Areas of MVFR VIS/CIG in SHRA will be possible, mainly over windward slopes, but could pop up nearly anywhere, with the potential for isolated IFR VIS/CIG in +SHRA/+TSRA.
AIRMET SIERRA for mountain obscuration is posted for windward Big Island, and may remain in place through the day. With the increasing E winds, AIRMET Tango may be required for low-level turbulence for areas SW through NW of the mountains.

Marine

With robust high pressure remaining far north and northeast of the area and a front approaching from the northwest, east to east- southeast winds will be moderate to fresh, and locally strong, over the next several days. A Small Craft Advisory (SCA) continues in effect for the typically windy zones around Maui County and the Big Island through tonight. More windward zones will likely be added later today or tonight as wind speeds are expected to marginally increase into the weekend.
The current small north-northwest swell will continue to fade. Another small pulse from the northwest is expected Friday. Surf along east facing shores will steadily rise through the end of the week due to the strengthening winds, likely peaking Friday into Saturday, then gradually decrease into early next week. Surf along south facing shores will remain above average through the end of the week, with a reinforcing south swell peaking later today into Friday just below advisory level, then gradually lowering beginning Friday night. South shore surf will drop back down to background levels by early next week.

HFO Watches/Warnings/Advisories

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

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Data Courtesy of NOAA.gov