Hilo

Tonight: Partly cloudy. Isolated showers and thunderstorms in the evening, then isolated showers after midnight. Lows 61 to 70 near the shore to 52 to 58 at 4000 feet. Light winds. Chance of rain 20 percent.

Saturday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs around 81 near the shore to 65 to 71 at 4000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Saturday Night: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 60 to 69 near the shore to 51 to 58 at 4000 feet. Light winds becoming northeast up to 10 mph after midnight. Chance of rain 40 percent.

Kona

Tonight: Mostly clear. Lows 69 to 74 near the shore to 49 to 54 near 5000 feet. Light winds.

Saturday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 82 to 87 near the shore to around 68 near 5000 feet. Light winds. Chance of rain 50 percent.

Saturday Night: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows 69 to 74 near the shore to 48 to 54 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

Tonight: Partly cloudy. Isolated showers and thunderstorms in the evening, then isolated showers after midnight. Lows 62 to 71 near the shore to 55 to 62 near 3000 feet. Light winds. Chance of rain 20 percent.

Saturday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 80 near the shore to 71 to 77 near 3000 feet. East winds up to 10 mph. Chance of rain 30 percent.

Saturday Night: Partly cloudy. Isolated showers in the evening. Lows 61 to 70 near the shore to 54 to 61 near 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Kohala

Tonight: Partly cloudy. Isolated showers and thunderstorms in the evening, then isolated showers after midnight. Lows 62 to 71 near the shore to 55 to 62 near 3000 feet. Light winds. Chance of rain 20 percent.

Saturday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 80 near the shore to 71 to 77 near 3000 feet. East winds up to 10 mph. Chance of rain 30 percent.

Saturday Night: Partly cloudy. Isolated showers in the evening. Lows 61 to 70 near the shore to 54 to 61 near 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

South Big Island

Tonight: Mostly clear. Isolated showers in the evening. Lows around 73 near the shore to around 54 near 5000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Saturday: Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 85 near the shore to around 68 near 5000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Saturday Night: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows around 73 near the shore to around 54 near 5000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Puna

Tonight: Partly cloudy. Isolated showers and thunderstorms in the evening, then isolated showers after midnight. Lows 61 to 70 near the shore to 52 to 58 at 4000 feet. Light winds. Chance of rain 20 percent.

Saturday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs around 81 near the shore to 65 to 71 at 4000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Saturday Night: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 60 to 69 near the shore to 51 to 58 at 4000 feet. Light winds becoming northeast up to 10 mph after midnight. Chance of rain 40 percent.

Waikoloa

Tonight: Partly cloudy. Lows 70 to 75 near the shore to 51 to 56 above 4000 feet. Light winds.

Saturday: Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 84 near the shore to 65 to 71 above 4000 feet. Northwest winds up to 10 mph. Chance of rain 40 percent.

Saturday Night: Mostly clear. Lows around 72 near the shore to 50 to 55 above 4000 feet. Light winds becoming northeast up to 10 mph after midnight.

Detailed Forecast

Synopsis

Showers and thunderstorms will continue into tonight, mainly over western islands. Light southeast surface winds will give way to increasing trade winds late Saturday through into Monday. A new area of increased moisture will move in Monday/Tuesday, with mainly windward showers. Southeast winds are likely to return late next week, but without as much moisture as our current southeast flow situation.

Discussion

Showers with isolated thunderstorms have covered parts of the state today, including a strongly rotating storm over Niihau early this morning. This storm was strengthen in part by strong wind shear and an interaction with an outflow boundary from previous convection. The rotation was strong enough to have produced a tornado, but due to the location of the event, we will likely never know if one actually occurred. Heavy rain was reported in several locations, including central Oahu, and flood advisories were in effect for Kauai and Oahu earlier today. Showers have moved mostly offshore as of 2 PM HST.
Additional showers and thunderstorms are in the forecast for tonight into early Saturday, and short range ensembles showing the main risk will remain over western islands. With light low- level winds, the enhanced moisture that has impacted the state this week will still be with us tonight and into Saturday. PW values range from roughly 1.5 to 1.8 inches. Therefore, episodes of brief moderate to heavy rainfall remain possible.
An important change in the weather is nearly here. After light southeast winds tonight into early Saturday, trades will move back late Saturday. They will become stronger out of the east Sunday, and even stronger from just north of east Monday. A new area of enhanced moisture will move in from the ENE around this time, enhancing windward showers into early Tuesday.
Trades are forecast to last through Wednesday night, with indications of a possible return to southeast flow late Thursday into Friday.

Aviation

Widespread light to moderate showers with embedded heavier convective elements are bringing MVFR to localized IFR conditions to Oahu this afternoon. Ample moisture remains in place through tonight as gentle offshore land breezes take hold over most areas. Even with the land breezes, stout SW flow aloft will likely carry pockets of moderate to locally heavy rain over leeward areas at times.
Light winds then give way to afternoon sea breezes on Saturday yielding the potential for convection over island interiors. Trades return late saturday evening.
AIRMET Sierra for mountain obscuration remains in effect for Oahu.

Marine

Scattered to numerous showers and isolated thunderstorms will continue over the western coastal waters tonight. While gusty winds can be expected around any thunderstorms, generally gentle to locally moderate southerly winds will continue, with light and variable winds to the far northwest. By late this weekend, easterly trade winds will gradually build from east to west with the potential for SCA conditions over the windier waters and channels around Maui County and the Big Island. Expect trades to strengthen further early next week as surface high pressure builds to the north.
The current moderate, medium period, north northwesterly swell (340-350 deg) peaked yesterday evening and has been slowly fading since. This north northwest swell will remain elevated through this evening and keep surf just shy of advisory levels through early Saturday along north facing shores. A small to moderate, medium period, northerly swell is progged to fill in late Saturday, along with a small, long to medium period west northwesterly swell. This combination of swells may boost surf heights back up Saturday night into Sunday, but should remain shy of High Surf Advisory criteria. Sunday night into early next week, the swell fades and should allow surf to drop to below seasonal averages.
Surf along east facing shores will remain small given the lack of trade winds upstream of the islands through Saturday, but areas exposed to the north swell will see an uptick through the rest of the weekend. As trade winds gradually strengthen later this weekend, east facing shores could become rough and choppy Sunday through early next week. Surf along south facing shores will remain flat to tiny through the weekend into early next week.

Fire weather

Showers, light southerly winds, and generally high relative humidities will continue into Saturday. This will keep conditions below critical fire thresholds through the next few days. The forecast shows little chance for dangerous fire weather well into next week.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov