Hilo

Tonight: Mostly cloudy with frequent showers. Lows 63 to 70 near the shore to around 56 at 4000 feet. North winds up to 10 mph. Chance of rain 80 percent.

Saturday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 79 to 86 near the shore to 64 to 69 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Saturday Night: Mostly cloudy with scattered showers. Lows 63 to 69 near the shore to 52 to 57 at 4000 feet. Northeast winds up to 10 mph shifting to the northwest after midnight. Chance of rain 50 percent.

Kona

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 73 near the shore to 49 to 54 near 5000 feet. Light winds. Chance of rain 50 percent.

Saturday: Mostly sunny with isolated showers in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 83 to 88 near the shore to around 67 near 5000 feet. South winds up to 10 mph shifting to the southwest in the afternoon. Chance of rain 50 percent.

Saturday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy after midnight. Lows 70 to 75 near the shore to around 51 near 5000 feet. Light winds. Chance of rain 50 percent.

Waimea

Tonight: Mostly cloudy with scattered showers. Lows 63 to 71 near the shore to 55 to 62 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Saturday: Breezy. Partly sunny with scattered showers. Highs 65 to 85. East winds 10 to 20 mph. Chance of rain 50 percent.

Saturday Night: Mostly cloudy with scattered showers. Lows 63 to 71 near the shore to 55 to 62 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Kohala

Tonight: Mostly cloudy with scattered showers. Lows 63 to 71 near the shore to 55 to 62 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Saturday: Breezy. Partly sunny with scattered showers. Highs 65 to 85. East winds 10 to 20 mph. Chance of rain 50 percent.

Saturday Night: Mostly cloudy with scattered showers. Lows 63 to 71 near the shore to 55 to 62 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

South Big Island

Tonight: Partly cloudy. Isolated showers in the evening. Lows around 74 near the shore to around 53 near 5000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Saturday: Breezy. Mostly sunny with isolated showers in the morning, then mostly cloudy with scattered showers in the afternoon. Highs around 85 near the shore to around 67 near 5000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Saturday Night: Partly cloudy. Isolated showers in the evening. Lows around 73 near the shore to around 52 near 5000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Puna

Tonight: Mostly cloudy with frequent showers. Lows 63 to 70 near the shore to around 56 at 4000 feet. North winds up to 10 mph. Chance of rain 80 percent.

Saturday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 79 to 86 near the shore to 64 to 69 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Saturday Night: Mostly cloudy with scattered showers. Lows 63 to 69 near the shore to 52 to 57 at 4000 feet. Northeast winds up to 10 mph shifting to the northwest after midnight. Chance of rain 50 percent.

Waikoloa

Tonight: Partly cloudy. Lows around 74 near the shore to around 55 above 4000 feet. East winds up to 15 mph.

Saturday: Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 84 to 90 near the shore to 66 to 73 above 4000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Saturday Night: Partly cloudy. Lows around 73 near the shore to around 53 above 4000 feet. Light winds.

Detailed Forecast

Synopsis

A moderate to locally breezy trade wind pattern will continue through tonight. Enhanced windward showers are expected this weekend as a weak disturbance moves through the region. A drier and more stable trade wind pattern will return early next week.

Discussion

Satellite and radar imagery show low clouds and isolated showers moving into windward areas on the moderate to locally breezy trades this afternoon, with an occasional shower or two making it into leeward areas at times. Low clouds and showers are also building up over some leeward areas across the Big Island, Maui and Oahu where sea breezes have developed. Temperature inversion heights were measured around 9000 feet at Lihue around 2 PM this afternoon and are allowing showers to deliver brief moderate downpours to these areas. In addition, patches of high clouds can also be seen moving across the region from the west with little to no impact on the sensible weather…but might make for a beautiful sunset this evening.
A shift in the pattern is expected for this this weekend. An upper level low will dip down over the state from the north Saturday night into Sunday, and a weak low level trough will move in from the east on the trades. With modest forcing in both the low to mid levels and pockets of low level moisture embedded in the trades, trade wind showers will likely be enhanced through the weekend, especially Saturday night into Sunday. Forecast soundings show temperature inversion heights lifting to at least 12,000 ft Saturday night/Sunday morning for locations across the northern half of the state, which will allow for greater vertical development in showers and potentially heavier rainfall rates. However, model QPF amounts are not reflecting any significant rainfall totals at this time.
In addition, cooler temperatures aloft will move overhead with the mid to upper level low, allowing instability to increase…which raises the question of whether or not we'll see any thunderstorms this weekend. With only marginal instability, small pockets of enhanced low level moisture, and weak surface forcing, decided to hold to the previous forecast philosophy and keep any mention of thunder out of the gridded forecast through the weekend.
A drier and more stable moderate trade wind pattern will return early next week as the upper level low and low level trough both move west of the state. Pockets of moisture will bring periods of overnight to early morning showers to mainly windward and mountain areas.

Aviation

Pockets of moisture moving along the moderate to locally breezy trade flow will generate periods of MVFR conditions along windward slopes, mainly at night and in the morning. VFR will prevail over leeward areas. No AIRMETs are in effect, though we will monitor for windward mountain obscuration tonight. An upper- level low will move over the state during the weekend and could bring a more active shower pattern with higher chances for MVFR conditions over windward areas by Saturday night.
Trade winds appear to be slightly too weak to produce significant low-level turbulence. However, low-level wind shear has been reported around Kahului, and conditions will remain conducive through late afternoon.

Marine

Fresh to strong easterly trade winds will continue through Saturday, then ease into the gentle to moderate range Sunday through Monday as a weak trough passes north of the state. A Small Craft Advisory (SCA) remains in effect for the windier waters around Maui County and the Big Island through Saturday. Fresh trade winds should return by Tuesday of next week and the trades may approach SCA thresholds for our typical windier waters around Maui County and the Big Island once again.
Surf along north facing shores will trend up through the first week of fall, beginning next Tuesday in response to a gale developing near the Kurils today, racing eastward across the Date Line near the Aleutians this weekend, then to the Gulf of Alaska early next week. Guidance shows this northwest swell peaking locally Tuesday night into Wednesday out of the northwest, then fading Thursday into Friday as it shifts out of a more north- northwest direction.
Surf along east facing shores will remain small and choppy into Saturday, then decrease Sunday into next week as the trades lower locally and upstream across the eastern Pacific.
Surf along south facing shores will remain small through the weekend, with mainly a mix of background long-period southwest and short-period southeast swells moving through. An upward trend is possible Tuesday through midweek due to a slightly larger southwest swell arriving.

HFO Watches/Warnings/Advisories

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

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Data Courtesy of NOAA.gov