Hilo

Tonight: Breezy. Cloudy with occasional showers. Lows 65 to 72 near the shore to around 57 at 4000 feet. Northeast winds up to 20 mph. Chance of rain 90 percent.

Saturday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 78 to 83 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. Scattered showers in the evening, then numerous showers after midnight. Lows 65 to 71 near the shore to 53 to 59 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 70 percent.

Kona

Tonight: Mostly cloudy with scattered showers in the evening, then mostly clear after midnight. Lows 68 to 76 near the shore to 53 to 58 near 5000 feet. Light winds. Chance of rain 40 percent.

Saturday: Sunny. Scattered showers in the afternoon. Highs 84 to 89 near the shore to around 69 near 5000 feet. Light winds. Chance of rain 40 percent.

Saturday Night: Mostly clear. Isolated showers in the evening. Lows 68 to 75 near the shore to 52 to 57 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then scattered showers after midnight. Lows 64 to 72 near the shore to 57 to 66 near 3000 feet. East winds 10 to 25 mph decreasing to up to 25 mph after midnight. Chance of rain 70 percent.

Saturday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 79 to 84 near the shore to 68 to 80 near 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Saturday Night: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Scattered showers. Lows 64 to 72 near the shore to 56 to 66 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Kohala

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then scattered showers after midnight. Lows 64 to 72 near the shore to 57 to 66 near 3000 feet. East winds 10 to 25 mph decreasing to up to 25 mph after midnight. Chance of rain 70 percent.

Saturday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 79 to 84 near the shore to 68 to 80 near 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Saturday Night: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Scattered showers. Lows 64 to 72 near the shore to 56 to 66 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

South Big Island

Tonight: Mostly clear. Breezy. Isolated showers in the evening. Lows around 76 near the shore to around 59 near 5000 feet. Northeast winds up to 25 mph. Chance of rain 20 percent.

Saturday: Sunny and breezy. Isolated showers in the afternoon. Highs around 84 near the shore to around 67 near 5000 feet. East winds up to 25 mph. Chance of rain 20 percent.

Saturday Night: Mostly clear. Isolated showers in the evening. Lows around 75 near the shore to around 58 near 5000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Puna

Tonight: Breezy. Cloudy with occasional showers. Lows 65 to 72 near the shore to around 57 at 4000 feet. Northeast winds up to 20 mph. Chance of rain 90 percent.

Saturday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 78 to 83 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. Scattered showers in the evening, then numerous showers after midnight. Lows 65 to 71 near the shore to 53 to 59 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 70 percent.

Waikoloa

Tonight: Mostly clear. Breezy. Isolated showers in the evening. Lows 71 to 76 near the shore to 53 to 59 above 4000 feet. Northeast winds up to 25 mph. Chance of rain 20 percent.

Saturday: Sunny and breezy. Isolated showers in the afternoon. Highs 84 to 90 near the shore to 67 to 72 above 4000 feet. Northeast winds up to 25 mph. Chance of rain 20 percent.

Saturday Night: Clear. Lows 70 to 75 near the shore to 51 to 58 above 4000 feet. Northeast winds up to 10 mph.

Detailed Forecast

Synopsis

Moderate to breezy trades will gradually strengthen through early next week, then weaken over the latter half. Brief pulses of enhanced showers will roll through on the trades during this time period, with showers favoring windward and mauka areas in the overnight to early morning hours.

Discussion

Radar and satellite imagery show isolated to scattered showers moving into mainly windward and mauka areas of the state this afternoon, with shower coverage increasing over the eastern half of the state as a plume of deeper moisture moves in on the weakly convergent trade wind flow. This uptick in windward shower activity will work its way up the island chain and persist into the evening hours before drier air fills in on Saturday.
Surface high pressure to the north will build through the weekend and strengthen the trade wind flow to breezy levels through early next week. Additional batches of increased moisture will continue to filter in on the trades over the next several days and bring brief upticks in windward and mauka shower activity, particularly during the overnight to early morning hours. Overall, these showers may produce brief moderate downpours at times, but they will move through rather quickly, so flooding is not expected to be an issue.
Both aloft and at the surface, broad and weak troughing will gradually develop over the Central Pacific by midweek, weakening the pressure gradient and therefore decreasing the trade wind speeds. Otherwise, periodic showers will continue to filter into windward and mauka areas on the weakening trade wind flow.
By next weekend, models are hinting at more substantial instability developing aloft and a larger area of deep tropical moisture being drawn up from the southeast, possibly leading to the potential for widespread heavy showers. However, the window with the greatest potential for any impacts is beyond the forecast period and with the model discrepancies that far out, forecast confidence is on the lower side for that period.

Aviation

Gusty trade winds will continue today into tomorrow. Shower coverage will increase from east to west during the next 24 hours, initially favoring windward portions of the Big Island and Maui, then spreading toward Oahu and Kauai tonight into tomorrow. Brief MVFR ceilings and visibility are expected in passing showers, with VFR conditions prevailing between showers.
AIRMET Sierra may be needed tonight as increasing shower coverage may bring renewed mountain obscuration.
AIRMET Tango remains for moderate low level turbulence downwind of island terrain.

Marine

Surface high pressure far north of the islands will strengthen as it drifts eastward through Saturday. Reinforcing high pressure will build far north of Hawaii on Sunday and will settle far northeast of the islands through early next week. Fresh to strong trade winds will prevail during this time, and the Small Craft Advisory (SCA) for the typically windy waters around Big Island and Maui may need to be expanded to additional waters this weekend. Trades are expected to ease slightly by Wednesday.
A medium-period north-northwest swell will peak overnight, producing north shore surf around seasonal average. This swell has been slow to arrive today, with measurements at NOAA buoy 51001 recently coming in at 5 to 6 feet at 11 to 12 seconds. This swell will slowly decline and shift more northerly during weekend as a smaller overlapping northwest swell moves through the area. Both swells will lower on Monday and fade on Tuesday. Another small northwest swell is possible next Thursday or Friday.
Long period south swell will peak through this evening, producing south shore surf slightly above seasonal average. This swell will gradually decline this weekend, and surf along south- facing shores will below average through the coming work week.
Surf along east-facing shores will gradually increase over the next couple of days as trade winds strengthen over the region. In addition, expect some wrapping north-northwest swell to reach exposed areas through at least Saturday. Rough trade wind swell will produce east shore surf above seasonal average Sunday through Tuesday, followed by a decline Wednesday.

Fire weather

Surface high pressure far north of the islands will produce moderate to breezy trade winds for the next few days, with gradual strengthening expected through early next week. Between batches of showers rolling through on the trades, RH levels may approach critical fire threshold ranges, particularly Saturday afternoon. Otherwise, RH levels should help to maintain low to moderate fire weather concerns.
Inversion heights should increase to around 10,000 feet through tonight as the current batch of deeper moisture rolls through, then drop to 5,000 to 7,000 feet on Saturday.

HFO Watches/Warnings/Advisories

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

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Data Courtesy of NOAA.gov