Hilo

Today: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs around 83 near the shore to 68 to 73 at 4000 feet. Northeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

Tonight: Showers. Locally heavy rainfall possible. Lows around 73 near the shore to around 58 at 4000 feet. North winds up to 15 mph. Chance of rain near 100 percent.

Saturday: Showers. Locally heavy rainfall possible. Highs around 82 near the shore to 67 to 72 at 4000 feet. North winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain near 100 percent.

Kona

Today: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 81 to 86 near the shore to around 68 near 5000 feet. Northwest winds up to 10 mph. Chance of rain 30 percent.

Tonight: Partly cloudy with scattered showers. Lows around 75 near the shore to around 57 near 5000 feet. Light winds. Chance of rain 30 percent.

Saturday: Partly sunny. Scattered showers in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs 80 to 86 near the shore to around 67 near 5000 feet. Light winds becoming west up to 10 mph in the afternoon. Chance of rain 50 percent.

Waimea

Today: Breezy. Mostly sunny with scattered showers. Highs around 81 near the shore to 68 to 78 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with numerous showers. Locally heavy rainfall possible. Lows around 73 near the shore to around 62 near 3000 feet. East winds 10 to 25 mph with gusts to 45 mph. Chance of rain 70 percent.

Saturday: Windy and showers. Locally heavy rainfall possible. Highs around 80 near the shore to 67 to 78 near 3000 feet. East winds 10 to 30 mph. Chance of rain near 100 percent.

Kohala

Today: Breezy. Mostly sunny with scattered showers. Highs around 81 near the shore to 68 to 78 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with numerous showers. Locally heavy rainfall possible. Lows around 73 near the shore to around 62 near 3000 feet. East winds 10 to 25 mph with gusts to 45 mph. Chance of rain 70 percent.

Saturday: Windy and showers. Locally heavy rainfall possible. Highs around 80 near the shore to 67 to 78 near 3000 feet. East winds 10 to 30 mph. Chance of rain near 100 percent.

South Big Island

Today: Sunny and breezy. Isolated showers in the afternoon. Highs around 85 near the shore to around 72 near 5000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with scattered showers. Lows 70 to 76 near the shore to around 55 near 5000 feet. Northeast winds up to 15 mph. Chance of rain 40 percent.

Saturday: Mostly cloudy. Windy. Numerous showers in the morning, then showers in the afternoon. Locally heavy rainfall possible. Highs around 85 near the shore to around 72 near 5000 feet. East winds up to 20 mph increasing to up to 30 mph in the afternoon. Chance of rain 90 percent.

Puna

Today: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs around 83 near the shore to 68 to 73 at 4000 feet. Northeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

Tonight: Showers. Locally heavy rainfall possible. Lows around 73 near the shore to around 58 at 4000 feet. North winds up to 15 mph. Chance of rain near 100 percent.

Saturday: Showers. Locally heavy rainfall possible. Highs around 82 near the shore to 67 to 72 at 4000 feet. North winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain near 100 percent.

Waikoloa

Today: Sunny and breezy. Isolated showers in the afternoon. Highs around 85 near the shore to 69 to 75 above 4000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with isolated showers. Lows around 76 near the shore to 53 to 61 above 4000 feet. East winds up to 25 mph. Chance of rain 20 percent.

Saturday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers and thunderstorms in the afternoon. Highs around 85 near the shore to 68 to 74 above 4000 feet. Northeast winds up to 20 mph with gusts to 45 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Breezy trade winds will increase in strength with gusty winds from Saturday into Sunday as weakening Hurricane Darby passes south of the island chain. These stronger winds may approach wind advisory levels and critical fire weather thresholds in some of our leeward areas on Saturday. Shower activity will increase on Saturday and Saturday night, especially for portions of Maui and the Big Island. Windward and mountain areas will see the highest rainfall coverage each day with gusty winds and less shower activity over leeward areas. The weather pattern returns to a moderate to breezy trade wind regime from Monday onward with passing showers mainly over windward and mountain areas, favoring the overnight to early morning hours.

Discussion

Looking at the satellite imagery this morning we see Hurricane Darby roughly 650 miles east-southeast of Hilo, Hawaii moving westward and weakening. Darby is forecast to continue to drift westward and weaken as it approaches the Hawaiian Islands, passing south of the Big Island on Saturday afternoon as a weak Tropical Storm. A narrow upper level trough and subtropical jet stream remain in place just northwest of the islands producing scattered to broken high level cirrus clouds across the region lasting into early next week. Bands of unstable (open cell) cumulus clouds in the lower levels are riding into the islands on the trade winds, expect passing shower activity through the early morning hours for all islands as these clouds drift over the state.
The large scale weather pattern continues to show a strong (1031 MB) high pressure center anchored roughly 1,200 miles north of Kauai. This system will produce moderate to breezy trade winds over the next seven days, however wind speeds will increase a bit in the short term, as the low pressure system associated with Darby passes south of the island chain this weekend. These stronger winds on Saturday may approach wind advisory levels for windier areas of each island and possibly trigger fire weather concerns for drier leeward locations (see Fire Weather section).
Deeper tropical moisture will drift into the eastern islands of Maui and the Big Island later tonight. Precipitable Water (PW) levels will increase into the 1.5 to 2.5 inch range. Instability and tropical moisture associated with the passage of Darby will lift the trade wind inversion heights into the 10,000 to 14,000 foot range, allowing deeper convective clouds to form, enhancing shower activity across the region. This deeper moisture and unstable showers will drift westward across the state on Saturday; reaching Molokai, Lanai and Oahu by Saturday afternoon, and Kauai County by Saturday night. Expect localized heavy rainfall over windward sections of Maui and Hawaii Counties from Friday night through Saturday afternoon. Isolated thunderstorms were added to the forecast for the mountain and leeward Big Island zones from Saturday afternoon to evening. More stable conditions will spread from East to West across the state from Sunday to Monday with decreasing shower trends.
On Monday and Tuesday, we see a drier moderate to breezy trade wind weather pattern for all islands with limited shower activity. More typical passing trade wind showers trend upward from Tuesday night onward with shower coverage favoring windward and mountain areas with brief showers possible over drier leeward areas.

Aviation

Breezy trade winds will continue today as high pressure remains anchored well north of the state. This pattern will focus a majority of showers and lower clouds to mainly windward areas and slopes through tonight. Mainly VFR conditions are expected to continue across most TAF locations through tonight. However, MVFR cigs will occasionally drift across windward areas from Oahu through Big Island today, as a band of low level moisture streams into the region, which will continue the need for AIRMET Sierra due to tempo mountain obscurations across some windward areas through this morning.
AIRMET Tango remains in effect for moderate low level turbulence over and downwind of terrain for all islands. These low level turbulent conditions are expected to continue through tonight.

Marine

The center of weakening Hurricane Darby is located far east- southeast of the Big Island early this morning. This system has been moving westward at about 14 kt. The Central Pacific Hurricane Center's latest forecast indicates Darby will continue to weaken, and it may be a tropical storm as it enters the far southeast offshore waters later tonight. This has required the issuance of a Tropical Storm Warning for portions of the Hawaiian offshore waters southeast of the Big Island.
A surface high pressure system will remain far north of the islands through early next week. In the near-term, the trades winds are expected to strengthen as Tropical Cyclone Darby moves closer to the region. In addition, combined seas will be elevated and rough due to a combination of local wind waves, and large south and east swells. The Small Craft Advisory (SCA) has been expanded to include all Hawaiian Waters starting this morning, and continuing through Saturday afternoon. The SCA also remains in effect for the typically windier waters adjacent to the islands of Maui County and the Big Island Saturday night. This SCA will likely be extended from Sunday through early next week.
We expect surf along south facing shores to be well above average this weekend. The initial forerunners of a new, large south swell will likely arrive later today or tonight. Surf produced by this swell is expected to peak on Saturday, with heights near the High Surf Warning threshold of 15 feet along south facing shores. This south swell will slowly subside from Sunday through early next week.
Surf along east facing shores will remain elevated and rough into early next week. Swells generated by Darby are expected to add to the mix, with the longer period energy arriving tonight, and likely peaking on Saturday. This swell will mainly impact east facing shores of the Big Island, where a High Surf Advisory may be required this weekend.

Fire weather

Wind speeds will increase on Saturday as Darby passes south of the Hawaiian Islands. There is a chance that windier leeward areas may briefly reach critical fire weather thresholds for some leeward fire zones from late morning to afternoon. These weather conditions will diminish rapidly from East to West as deeper moisture associated with Darby increases humidity levels and shower activity across the island chain.

HFO Watches/Warnings/Advisories

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