Hilo

Rest Of Today: Occasional showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 74 to 80 near the shore to around 61 at 4000 feet. North winds 10 to 15 mph shifting to the northeast in the afternoon. Gusts up to 40 mph. Chance of rain near 100 percent.

Tonight: Frequent showers and slight chance of thunderstorms. Lows 62 to 71 near the shore to 53 to 58 at 4000 feet. Northwest winds up to 15 mph. Chance of rain near 100 percent.

Sunday: Frequent showers and slight chance of thunderstorms. Highs 78 to 84 near the shore to around 65 at 4000 feet. Northeast winds up to 10 mph. Chance of rain near 100 percent.

Kona

Rest Of Today: Mostly cloudy. Showers likely and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 77 near the shore to around 64 near 5000 feet. Northwest winds up to 10 mph. Chance of rain 70 percent.

Tonight: Cloudy. Slight chance of thunderstorms and isolated showers in the evening, then slight chance of thunderstorms after midnight. Lows 65 to 70 near the shore to 48 to 55 near 5000 feet. Light winds. Chance of rain 20 percent.

Sunday: Cloudy. Slight chance of thunderstorms in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Highs around 81 near the shore to around 68 near 5000 feet. Light winds. Chance of rain 70 percent.

Waimea

Rest Of Today: Windy. Occasional showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs around 76 near the shore to 66 to 71 near 3000 feet. East winds 10 to 30 mph. Chance of rain near 100 percent.

Tonight: Breezy. Numerous showers and slight chance of thunderstorms in the evening, then frequent showers and slight chance of thunderstorms after midnight. Lows around 64 near the shore to 55 to 62 near 3000 feet. East winds 10 to 25 mph decreasing to up to 25 mph after midnight. Chance of rain near 100 percent.

Sunday: Breezy. Frequent showers and slight chance of thunderstorms in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Highs around 80 near the shore to 70 to 75 near 3000 feet. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain near 100 percent.

Kohala

Rest Of Today: Windy. Occasional showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs around 76 near the shore to 66 to 71 near 3000 feet. East winds 10 to 30 mph. Chance of rain near 100 percent.

Tonight: Breezy. Numerous showers and slight chance of thunderstorms in the evening, then frequent showers and slight chance of thunderstorms after midnight. Lows around 64 near the shore to 55 to 62 near 3000 feet. East winds 10 to 25 mph decreasing to up to 25 mph after midnight. Chance of rain near 100 percent.

Sunday: Breezy. Frequent showers and slight chance of thunderstorms in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Highs around 80 near the shore to 70 to 75 near 3000 feet. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain near 100 percent.

South Big Island

Rest Of Today: Mostly cloudy. Windy. Scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 77 near the shore to around 65 near 5000 feet. East winds up to 30 mph. Chance of rain 50 percent.

Tonight: Cloudy and breezy. Slight chance of thunderstorms and isolated showers in the evening, then slight chance of thunderstorms after midnight. Lows 66 to 72 near the shore to around 51 near 5000 feet. Northeast winds up to 25 mph becoming 10 to 20 mph after midnight. Chance of rain 20 percent.

Sunday: Breezy. Cloudy with slight chance of thunderstorms in the morning, then partly sunny with numerous showers and slight chance of thunderstorms in the afternoon. Highs around 81 near the shore to around 69 near 5000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Puna

Rest Of Today: Occasional showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 74 to 80 near the shore to around 61 at 4000 feet. North winds 10 to 15 mph shifting to the northeast in the afternoon. Gusts up to 40 mph. Chance of rain near 100 percent.

Tonight: Frequent showers and slight chance of thunderstorms. Lows 62 to 71 near the shore to 53 to 58 at 4000 feet. Northwest winds up to 15 mph. Chance of rain near 100 percent.

Sunday: Frequent showers and slight chance of thunderstorms. Highs 78 to 84 near the shore to around 65 at 4000 feet. Northeast winds up to 10 mph. Chance of rain near 100 percent.

Waikoloa

Rest Of Today: Cloudy and breezy. Scattered showers and slight chance of thunderstorms in the morning, then showers likely and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 77 near the shore to 60 to 67 above 4000 feet. Northeast winds up to 25 mph with gusts to 45 mph. Chance of rain 70 percent.

Tonight: Breezy. Cloudy with slight chance of thunderstorms and isolated showers. Lows 66 to 71 near the shore to 50 to 55 above 4000 feet. East winds up to 25 mph. Chance of rain 20 percent.

Sunday: Cloudy with slight chance of thunderstorms and isolated showers in the morning, then partly sunny with scattered showers and slight chance of thunderstorms in the afternoon. Highs around 81 near the shore to 64 to 71 above 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A transition to a wet trade wind pattern is in store for portions of the state this weekend as an upper trough settles southward into the area. Windward and mauka showers will increase in coverage, with some making it into our dry leeward areas periodically with the gusty trades in place. The best chance for heavy showers and even a few thunderstorms that could lead to flash flooding will be over the eastern end of the state. A return of drier trade wind conditions is expected early next week.

Discussion

Guidance remains in good agreement and depicts a wet pattern evolving over the state today as upper heights lower in response to a short wave trough settling southward into the area. This transition has already begun for the windward areas of the Big Island this morning and is expected for most of the state today and tonight. Showers will become heavy at times, which increases the threat for flash flooding – in the event of anchoring or where they become focused over time. High-resolution model guidance supports this and depicts peak 48-hour rainfall accumulations reaching/exceeding the 6 to 10 inch range for some windward areas of Maui and the Big Island, which would drive water levels in the impacted streams up to and beyond critical levels if realized. This potential has led to the issuance of a Flood Watch through tonight for Maui County and the Big Island and a Winter Storm Warning for the Big Island Summits above 12000 ft for the potential of heavy snow. Although the best chance for this threat is over the eastern end of the state, a few heavy showers can't be ruled out across the western end as well – with some showers spilling over into our dry leeward areas where drought conditions are occurring. In addition to the rainfall potential, the added instability and deep moisture supports a few thunderstorms.
A low will pinch off from the upper trough and move away to the southwest on Monday, resulting in a transition to a drier and more stable trade wind weather regime, which will continue through the at least the middle of the week.

Aviation

High pressure ridge north of the state will maintain moderate to breezy trade winds throughout the weekend, anchoring a majority of showers along northeast facing slopes and coasts. Current radar trends show mainly scattered showers over windward slopes this evening, however showers are expected to increase in intensity and areal coverage through Saturday as an upper trough drifts across the islands.
AIRMET for MVFR cigs and vsby will continue over windward Big Island toward Maui, with MVFR cigs and vsby and tempo mtn obsc possibly expanding across neighboring islands later tonight through Saturday as conditions continue to deteriorate.
AIRMET Tango for low level mechanical turbulence to the lee of higher terrain remains in effect, and is expected to continue through Saturday. Additionally, a period for tempo light ice will increase across the islands from west to east through Saturday as deeper mid and upper lvl moisture builds in overhead.

Marine

High pressure northwest of the islands will keep moderate to strong trades in place through the forecast period, with only minor variations in strength. The Small Craft Advisory (SCA) has been expanded to include most areas from the Leeward Oahu waters eastward through 6 PM Sunday. This SCA may need to be extended for some marine zones through much of next week.
East shore surf will remain close to seasonal levels today, before lowering to below normal levels Sunday through late next week as the trade winds diminish upstream of the island chain.
South shore surf will remain at slightly above normal levels today through Monday as a moderate size south swell moves through. Surf will then lower back to seasonal levels Tuesday through the end of the upcoming work week.
A series of small northwest swells will move through the area today through Monday, maintaining small surf along north facing shores. A larger, long period northwest swell associated with former tropical cyclone Malakas will arrive Monday night and Tuesday, giving a noticeable boost to surf along north and west facing shores Tuesday through late next week.

HFO Watches/Warnings/Advisories

Wind Advisory until 6 PM HST this evening for Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Kohala, Big Island Interior, Lanai Windward, Lanai Leeward, Lanai South, Maui Central Valley North, Maui Central Valley South, Windward Haleakala, Kipahulu, South Haleakala, Big Island South, Big Island Southeast, Big Island North.
Winter Storm Warning until 6 AM HST Sunday for Big Island Summits.
Small Craft Advisory until 6 PM HST Sunday for Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov