Photo Credit: James Grenz

Hilo

Today: Occasional showers in the morning, then occasional showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the morning. Highs 77 to 85 near the shore to 63 to 69 at 4000 feet. Southeast winds up to 10 mph. Chance of rain near 100 percent.

Tonight: Mostly cloudy. Occasional showers and slight chance of thunderstorms early in the evening, then showers likely in the late evening and overnight. Lows 65 to 72 near the shore to around 58 at 4000 feet. Southeast winds around 10 mph shifting to the west after midnight. Chance of rain 90 percent.

Saturday: Mostly cloudy. Showers likely in the morning, then scattered showers in the afternoon. Highs 78 to 84 near the shore to 63 to 69 at 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Kona

Today: Mostly sunny with isolated showers in the morning, then mostly cloudy with scattered showers and slight chance of thunderstorms in the afternoon. Highs 83 to 89 near the shore to around 69 near 5000 feet. Light winds. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers and slight chance of thunderstorms early in the evening, then scattered showers in the late evening and overnight. Lows 71 to 77 near the shore to 51 to 58 near 5000 feet. Light winds becoming northeast around 10 mph after midnight. Chance of rain 50 percent.

Saturday: Partly sunny. Scattered showers in the afternoon. Highs 82 to 89 near the shore to around 69 near 5000 feet. Northeast winds around 10 mph. Chance of rain 50 percent.

Waimea

Today: Partly sunny. Breezy. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Highs 66 to 86. East winds up to 15 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers and slight chance of thunderstorms early in the evening, then scattered showers in the late evening and overnight. Lows 65 to 72 near the shore to 57 to 65 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Saturday: Breezy. Partly sunny with scattered showers. Highs 65 to 86. East winds 10 to 20 mph. Chance of rain 50 percent.

Kohala

Today: Partly sunny. Breezy. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Highs 66 to 86. East winds up to 15 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers and slight chance of thunderstorms early in the evening, then scattered showers in the late evening and overnight. Lows 65 to 72 near the shore to 57 to 65 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Saturday: Breezy. Partly sunny with scattered showers. Highs 65 to 86. East winds 10 to 20 mph. Chance of rain 50 percent.

South Big Island

Today: Mostly cloudy. Windy. Scattered showers in the morning, then showers likely and slight chance of thunderstorms in the afternoon. Highs around 84 near the shore to around 67 near 5000 feet. East winds 10 to 30 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers and slight chance of thunderstorms early in the evening, then scattered showers in the late evening and overnight. Lows around 74 near the shore to around 54 near 5000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Saturday: Partly sunny. Breezy. Isolated showers in the afternoon. Highs around 84 near the shore to around 67 near 5000 feet. East winds 15 to 25 mph. Chance of rain 20 percent.

Puna

Today: Occasional showers in the morning, then occasional showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the morning. Highs 77 to 85 near the shore to 63 to 69 at 4000 feet. Southeast winds up to 10 mph. Chance of rain near 100 percent.

Tonight: Mostly cloudy. Occasional showers and slight chance of thunderstorms early in the evening, then showers likely in the late evening and overnight. Lows 65 to 72 near the shore to around 58 at 4000 feet. Southeast winds around 10 mph shifting to the west after midnight. Chance of rain 90 percent.

Saturday: Mostly cloudy. Showers likely in the morning, then scattered showers in the afternoon. Highs 78 to 84 near the shore to 63 to 69 at 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Waikoloa

Today: Mostly sunny in the morning, then partly sunny with slight chance of thunderstorms and isolated showers in the afternoon. Highs 83 to 89 near the shore to 66 to 72 above 4000 feet. Light winds. Gusts up to 25 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy. Slight chance of thunderstorms and isolated showers early in the evening, then isolated showers in the late evening and overnight. Lows around 75 near the shore to 53 to 58 above 4000 feet. Light winds becoming east around 10 mph after midnight. Gusts up to 30 mph. Chance of rain 20 percent.

Saturday: Partly sunny. Highs 82 to 89 near the shore to 66 to 72 above 4000 feet. Northeast winds around 10 mph.

Detailed Forecast

Synopsis

Moderate to locally breezy east-southeast winds will continue through Saturday, then become easterly on Sunday, and continue into next week. The island atmosphere will be somewhat unstable through Saturday, with some locally heavy downpours possible, especially over windward portions of Maui and the Big Island. A more typical trade wind weather regime is expected by Sunday.

Discussion

Generally speaking, surface high pressure to the distant NE will ensure that a trade wind flow persists over the islands through the weekend, and well into next week. In the short term, the flow will be veered to the SE (especially at cloud level) as a slow-moving and persistent frontal boundary NW of the islands creeps closer. The boundary is expected to eventually stall about 400 miles W of Kauai on Sunday, then gradually dissipate early next week. This should allow the moderate to breezy E-SE trade winds to back to a more typical easterly direction by early next week, with little significant change through the middle of the week.
Aloft, a persistent and large blocking high to the NE of the islands has a low moving W along it's southwestern periphery, with water vapor imagery indicating the low is centered about 300 miles NNW of Kauai. The presence of this low has destabilized the island atmosphere, with morning soundings indicating an unstable profile. Scattered thunderstorms are developing just S and E of the low's center, where instability is maximized. Closer to the islands, waves of moderate to heavy showers have been moving into windward and SE portions of the Big Island and Maui throughout the night. Elsewhere, fast-moving heavy showers are headed NW near 30 mph over windward waters from Oahu to the Big Island, and over waters NW of Kauai, with thunderstorms just N of the Kauai and Oahu coastal waters. Just a few windward showers have been noted over the islands from Molokai to Kauai. Scattered to broken high clouds are moving over the islands within a WSW flow aloft while scattered to broken low clouds are streaming in from the E toward Maui and the Big Island.
The low aloft will track W and NW over the next 2 days or so, maintaining a somewhat unstable island atmosphere, with warming mid- level temperatures expected thereafter as the low dissipates and a weak ridge develops. With the moderate to locally strong E-SE low- level flow being weakly convergent and fairly moist, guidance indicates that spotty locally heavy showers could develop into Saturday, with some showers potentially briefly dampening leeward locations. Showers are expected to be most prevalent over windward and SE portions of the Big Island and Maui, with Kauai and Oahu in the rain and wind shadow of Maui and the Big Island to a certain degree. Mid- and high-level clouds are also expected to thicken today, likely continuing into Saturday before diminishing.
A fairly typical trade wind weather pattern is expected for early to mid next week, with brief windward showers and little to no high cloudiness. Long-range guidance indicates the potential for a bit of a pattern shift as the blocking high to the N breaks down, potentially allowing a low aloft to move over the area in about a week.

Aviation

Surface high pressure located northeast of Hawaii bring moderate to locally breezy east southeast flow to the region through the forecast period.
An upper level low situated around 300 miles north northwest of Kauai will help to generate deeper low level clouds and enhance shower activity over the state. Eastern portions of the Big Island and Maui may receive pockets of heavier rain with accompanying MVFR and brief IFR conditions. Scattered showers with brief MVFR conditions may also occur along mainly windward portions of the remaining smaller islands.
AIRMET Sierra remains in effect for north thru eastern portions of the Big Island and Maui above 2000 feet due to clouds and showers.
AIRMET Tango remains in effects for Molokai Maui and the Big Island below 9000 feet over and immediately south through northwest of mountains due to tempo moderate turbulence.

Marine

Robust high pressure remains far north and northeast of the islands, while a front slowly approaches from the northwest. This pattern will sustain moderate to fresh, and locally strong, east to east- southeast winds through the weekend. A Small Craft Advisory (SCA) continues across the typically windy zones around Maui County and the Big Island, and was expanded earlier to include most waters east of the Kauai Channel through early Saturday morning. Also, combined seas will reach or exceed the 10-foot SCA threshold in some waters.
A small swell from the northwest will continue through the weekend. Surf along east facing shores will steadily rise due to the strengthening winds. East shore surf will remain elevated through the weekend before gradually diminishing by early next week. Surf along south facing shores will also remain above average, with a reinforcing south swell arriving today. South shore surf will drop back down to background levels by early next week.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Saturday for Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov