Hilo

Today: Partly sunny. Breezy. Showers likely early in the morning, then scattered showers in the late morning and afternoon. Highs 81 to 87 near the shore to around 70 at 4000 feet. North winds up to 20 mph shifting to the northeast 10 to 20 mph in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy. Breezy. Showers likely in the evening, then occasional showers after midnight. Lows 69 to 75 near the shore to around 54 at 4000 feet. Northeast winds 10 to 20 mph. Chance of rain 90 percent.

Saturday: Mostly cloudy. Showers likely in the morning, then scattered showers in the afternoon. Highs 82 to 88 near the shore to around 70 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Kona

Today: Sunny early in the morning, then partly sunny with scattered showers in the late morning and afternoon. Highs 82 to 87 near the shore to 67 to 72 near 5000 feet. West winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then mostly clear with isolated showers after midnight. Lows 69 to 75 near the shore to around 54 near 5000 feet. West winds up to 10 mph shifting to the southeast around 10 mph after midnight. Chance of rain 50 percent.

Saturday: Sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 82 to 87 near the shore to 67 to 72 near 5000 feet. Light winds. Chance of rain 50 percent.

Waimea

Today: Windy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 82 near the shore to 75 to 80 near 3000 feet. East winds 10 to 30 mph. Chance of rain 50 percent.

Tonight: Windy. Mostly cloudy with scattered showers. Lows around 70 near the shore to 56 to 62 near 3000 feet. East winds 15 to 30 mph decreasing to 10 to 20 mph after midnight. Chance of rain 50 percent.

Saturday: Partly sunny with scattered showers. Highs around 83 near the shore to 75 to 80 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Kohala

Today: Windy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 82 near the shore to 75 to 80 near 3000 feet. East winds 10 to 30 mph. Chance of rain 50 percent.

Tonight: Windy. Mostly cloudy with scattered showers. Lows around 70 near the shore to 56 to 62 near 3000 feet. East winds 15 to 30 mph decreasing to 10 to 20 mph after midnight. Chance of rain 50 percent.

Saturday: Partly sunny with scattered showers. Highs around 83 near the shore to 75 to 80 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

South Big Island

Today: Breezy. Sunny early in the morning, then partly sunny with isolated showers in the late morning and afternoon. Highs around 84 near the shore to around 74 near 5000 feet. Northeast winds 10 to 25 mph shifting to the east up to 25 mph in the afternoon. Gusts up to 50 mph. Chance of rain 20 percent.

Tonight: Breezy. Mostly cloudy with isolated showers in the evening, then mostly clear after midnight. Lows around 70 near the shore to around 53 near 5000 feet. East winds up to 25 mph with gusts to 45 mph becoming 10 to 20 mph after midnight. Chance of rain 20 percent.

Saturday: Sunny in the morning, then cloudy with isolated showers in the afternoon. Highs around 84 near the shore to around 74 near 5000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Puna

Today: Partly sunny. Breezy. Showers likely early in the morning, then scattered showers in the late morning and afternoon. Highs 81 to 87 near the shore to around 70 at 4000 feet. North winds up to 20 mph shifting to the northeast 10 to 20 mph in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy. Breezy. Showers likely in the evening, then occasional showers after midnight. Lows 69 to 75 near the shore to around 54 at 4000 feet. Northeast winds 10 to 20 mph. Chance of rain 90 percent.

Saturday: Mostly cloudy. Showers likely in the morning, then scattered showers in the afternoon. Highs 82 to 88 near the shore to around 70 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Waikoloa

Today: Mostly sunny. Windy. Highs 83 to 88 near the shore to 68 to 75 above 4000 feet. East winds up to 30 mph shifting to the northeast 10 to 30 mph in the afternoon. Gusts up to 50 mph.

Tonight: Partly cloudy. Windy. Lows around 73 near the shore to 51 to 58 above 4000 feet. Northeast winds 10 to 30 mph with gusts to 50 mph shifting to the east 10 to 15 mph after midnight.

Saturday: Mostly sunny. Highs 83 to 88 near the shore to 68 to 75 above 4000 feet. Northeast winds around 10 mph.

Detailed Forecast

Synopsis

Strong trade winds on Friday will ease slightly on Saturday, diminish more substantially Sunday, and then remain on the lighter side for most of next week. The trades will deliver passing clouds and showers to windward areas, with a few showers drifting leeward while the trades remain strong. When the trades diminish, passing windward showers will likely diminish in frequency, while leeward areas may see some afternoon clouds and showers.

Discussion

Trade winds will strengthen tonight and Friday as high pressure to the distant NE moves W and builds slightly. Moisture embedded in the trades will provide for passing showers through Friday morning over windward and mauka areas, with showers spreading leeward on all islands but the Big Island, where afternoon pop-up showers will linger into the evening. Winds may become sufficiently strong in terrain-accelerated areas of Maui and Hawaii Counties to warrant a Wind Advisory on Friday.
The high will remain nearly stationary but weaken somewhat on Saturday, with winds expected to diminish ever-so-slightly. A more significant reduction in trade wind speeds is expected Sunday and Monday as a low and front pass far N of the area. This will weaken the high while also splitting it into two centers to the NW and NE of the islands, with a break in the associated ridge to the N of the islands.
Another reason the winds will remain light for most of next week will be due to the presence of yet another cutoff closed low to the N of the islands inducing the formation a weak and broad surface trough. Aloft, this feature is currently an E-W trough near 30N 152W. In this case, the developing low is expected to linger several hundred miles to the NNE of the islands at its closest approach. It may drift close enough to introduce modest instability to the islands atmosphere beginning early next week. The light trades may deliver a few windward showers during nights and mornings, with afternoon sea breezes driving clouds and a few showers over leeward areas. The intensity of these showers will be dependent on how close the low gets to the islands, but the potential for a few heavy showers appears to exist.

Aviation

Surface high pressure north of the islands will maintain strong breezy trade winds across the area through Friday. AIRMET Tango for low level turbulence below 8k feet, south through west of all mountain ranges, will continue until further notice. Random clouds and showers embedded in this trade wind flow will favor the windward and mountain areas, causing brief MVFR ceiling and vis. The frequency of these clouds and showers will be highest during the morning hours. A shower or two is still possible along the Kona coast of the Big Island this evening. Afternoon clouds will reappear over the lee side of the Big Island tomorrow with a few showers.

Marine

A high north of the state will drive stronger trade winds across local waters through Saturday. A Small Craft Advisory (SCA) remains in effect through Saturday afternoon for all waters through tomorrow. Trades will gradually weaken tomorrow night through Saturday, thus the SCA will be scaled back to the typical windy waters around Maui County and the Big Island. Winds will then become light to moderate the rest of the weekend into early next week.
A small, long period south swell filling in through Saturday will be reinforced by small, medium period south and low period southeast swells over the next several days. These swells will maintain near seasonal south facing shore surf through the holiday weekend. A series of small, medium to slightly longer period south swells will arrive Labor Day and hold through most of next week. Strengthened trades over and upstream of the islands will provide a bump to the east facing shore surf by another foot or two into the weekend.

Fire weather

With locally strong trade winds expected on Friday, and the Keetch- Byram Drought Index (KBDI) over 600, critical fire weather behavior is possible over leeward areas Friday late morning/afternoon as dew points over leeward areas lower into the mid-60s. A Fire Weather Watch is posted for leeward areas of nearly all islands. Although winds may ease slightly on Saturday, similar conditions are possible Saturday afternoon.

HFO Watches/Warnings/Advisories

Fire Weather Watch from Friday morning through Friday afternoon for Kauai Leeward, Oahu South Shore, Waianae Coast, Oahu North Shore, Olomana, Central Oahu, Waianae Mountains, Molokai Leeward, Maui Leeward West, Maui Central Valley, Leeward Haleakala, Kona, Kohala, Big Island Interior.
Small Craft Advisory until 6 PM HST Saturday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.
Small Craft Advisory until 6 PM HST Friday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Big Island Windward Waters.

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Data Courtesy of NOAA.gov