Photo Credit: Tyler Rooke

West Side

Rest Of Today: Windy. Mostly cloudy with scattered showers and slight chance of thunderstorms. Locally heavy rainfall possible in the afternoon. Highs 75 to 82. Northeast winds 20 to 30 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers and slight chance of thunderstorms. Lows 66 to 72. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Sunday: Breezy. Mostly cloudy with scattered showers and slight chance of thunderstorms in the morning, then mostly sunny with scattered showers in the afternoon. Highs 79 to 86. Northeast winds 10 to 25 mph. Chance of rain 50 percent.

South Side

Rest Of Today: Mostly cloudy. Windy. Isolated showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 81. Northeast winds 10 to 30 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Slight chance of thunderstorms and isolated showers after midnight. Lows 64 to 72. North winds 10 to 20 mph. Chance of rain 20 percent.

Sunday: Breezy. Mostly cloudy with slight chance of thunderstorms and isolated showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 85. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

North Shore

Rest Of Today: Breezy. Occasional showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 72 to 78 near the shore to around 62 near 5000 feet. East winds 10 to 25 mph decreasing to up to 25 mph in the afternoon. 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 68 near the shore to 46 to 53 near 5000 feet. East winds up to 20 mph. Chance of rain near 100 percent.

Sunday: Breezy. Frequent showers and slight chance of thunderstorms in the morning, then frequent showers in the afternoon. Highs 76 to 82 near the shore to around 62 near 5000 feet. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain near 100 percent.

Central Maui

Rest Of Today: Breezy. Scattered showers and slight chance of thunderstorms in the morning, then occasional showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 77 to 82. Northeast winds 15 to 25 mph. Chance of rain near 100 percent.

Tonight: Breezy. Mostly cloudy with slight chance of thunderstorms and isolated showers. Lows 64 to 70. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Sunday: Breezy. Mostly cloudy with slight chance of thunderstorms and isolated showers in the morning, then mostly sunny with scattered showers in the afternoon. Highs 81 to 86. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

Upcountry

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 56 at the visitor center to around 53 at the summit. East winds up to 20 mph. Chance of rain 70 percent.

Tonight: Cloudy with scattered showers and slight chance of thunderstorms. Lows around 45 at the visitor center to around 41 at the summit. East winds up to 15 mph. Chance of rain 50 percent.

Sunday: Cloudy with scattered showers and slight chance of thunderstorms in the morning, then partly sunny with scattered showers in the afternoon. Highs around 56 at the visitor center to around 53 at the summit. East winds up to 15 mph. Chance of rain 50 percent.

East Maui

Rest Of Today: Breezy. Occasional showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 72 to 78 near the shore to around 62 near 5000 feet. East winds 10 to 25 mph decreasing to up to 25 mph in the afternoon. 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 68 near the shore to 46 to 53 near 5000 feet. East winds up to 20 mph. Chance of rain near 100 percent.

Sunday: Breezy. Frequent showers and slight chance of thunderstorms in the morning, then frequent showers in the afternoon. Highs 76 to 82 near the shore to around 62 near 5000 feet. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain near 100 percent.

Lanai City

Rest Of Today: Cloudy and breezy. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 67 to 74. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers and slight chance of thunderstorms. Lows around 63. Northeast winds 10 to 20 mph. Chance of rain 30 percent.

Sunday: Mostly cloudy. Breezy. Scattered showers and slight chance of thunderstorms in the morning, then scattered showers in the afternoon. Highs 71 to 78. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Kaunakakai

Rest Of Today: Breezy. Cloudy with scattered showers and slight chance of thunderstorms. Locally heavy rainfall possible in the afternoon. Highs 73 to 81. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers and slight chance of thunderstorms in the evening, then slight chance of thunderstorms and isolated showers after midnight. Lows 64 to 74. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Sunday: Partly sunny. Breezy. Slight chance of thunderstorms and isolated showers in the morning, then scattered showers in the afternoon. Highs 77 to 85. Northeast winds 15 to 25 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