Hilo

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 65 to 71 near the shore to 50 to 56 at 4000 feet. Northeast winds up to 10 mph shifting to the west after midnight. Chance of rain 70 percent.

Friday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 79 to 86 near the shore to around 69 at 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers. Lows 67 to 73 near the shore to 52 to 57 at 4000 feet. East winds up to 10 mph shifting to the south around 10 mph after midnight. Chance of rain 50 percent.

Kona

Tonight: Mostly cloudy with numerous showers in the evening, then partly cloudy with scattered showers after midnight. Lows around 73 near the shore to 47 to 53 near 5000 feet. West winds up to 10 mph in the evening becoming light. Chance of rain 70 percent.

Friday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 85 near the shore to around 67 near 5000 feet. West winds around 10 mph. Chance of rain 50 percent.

Friday Night: Partly cloudy. Scattered showers in the evening. Lows around 73 near the shore to 48 to 55 near 5000 feet. Northwest winds up to 10 mph in the evening becoming light. Chance of rain 40 percent.

Waimea

Tonight: Partly cloudy with isolated showers. Lows 64 to 71 near the shore to 56 to 61 near 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Friday: Mostly sunny with isolated showers. Highs 76 to 82 near the shore to 70 to 79 near 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Friday Night: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 65 to 71 near the shore to 57 to 63 near 3000 feet. East winds 10 to 15 mph. Chance of rain 40 percent.

Kohala

Tonight: Partly cloudy with isolated showers. Lows 64 to 71 near the shore to 56 to 61 near 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Friday: Mostly sunny with isolated showers. Highs 76 to 82 near the shore to 70 to 79 near 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Friday Night: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 65 to 71 near the shore to 57 to 63 near 3000 feet. East winds 10 to 15 mph. Chance of rain 40 percent.

South Big Island

Tonight: Partly cloudy. Scattered showers in the evening. Lows around 72 near the shore to around 50 near 5000 feet. East winds 10 to 15 mph. Chance of rain 40 percent.

Friday: Sunny. Isolated showers in the afternoon. Highs around 86 near the shore to around 66 near 5000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Friday Night: Mostly clear. Breezy. Lows around 73 near the shore to around 51 near 5000 feet. East winds 10 to 20 mph.

Puna

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 65 to 71 near the shore to 50 to 56 at 4000 feet. Northeast winds up to 10 mph shifting to the west after midnight. Chance of rain 70 percent.

Friday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 79 to 86 near the shore to around 69 at 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers. Lows 67 to 73 near the shore to 52 to 57 at 4000 feet. East winds up to 10 mph shifting to the south around 10 mph after midnight. Chance of rain 50 percent.

Waikoloa

Tonight: Mostly clear with scattered showers. Lows around 73 near the shore to 50 to 56 above 4000 feet. Northeast winds 10 to 15 mph shifting to the east after midnight. Chance of rain 50 percent.

Friday: Mostly sunny with scattered showers. Highs 84 to 90 near the shore to 66 to 74 above 4000 feet. North winds 10 to 15 mph. Chance of rain 50 percent.

Friday Night: Mostly clear. Lows around 74 near the shore to 51 to 56 above 4000 feet. East winds around 10 mph.

Detailed Forecast

Synopsis

High pressure far northeast of the state will remain in place through the next few days. Showers will favor windward and mountain areas, especially during the overnight through early morning hours. This weekend, trades will increase and much drier air will move into the region. Shower trends will increase again from Monday onward as trades return to the moderate to locally breezy range.

Discussion

Moderate to locally breezy easterly trade winds are prevailing across the main Hawaiian Islands this afternoon, steered by high pressure that remains nearly stationary far northeast of the state. Embedded within these trades are isolated to widely scattered showers, though observations from rain gauge networks across the state show that rainfall amounts have been minimal. Daytime convergence has also increased cloud cover and produced isolated showers across the Kona slopes of the Big Island since late morning. Meanwhile, the latest upper air soundings from Hilo and Lihue show stable conditions with strong inversions between about 5,000 and 6,500 feet and less available low-level moisture when compared to this same time yesterday afternoon.
A low level trough east of the islands will continue to drift westward towards the state, passing over the islands tonight through Friday. This trough is expected to briefly increase inversion heights, producing deeper clouds and increasing shower trends, especially over the western islands through Friday. However, overall rainfall amounts are expected to remain limited. The best chances for showers through Friday will remain across windward and mountain areas, especially during the overnight through early morning hours.
This weekend, however, a much drier air mass will be ushered into the region as the high pressure to the northeast strengthens. As the previous discussion mentioned, temperature inversion heights may drop into the 4,000 to 5,000 ft range this weekend, increasing wind speeds and limiting cloud and shower development. Much lower humidity levels due to the drier air mass and locally windy trade winds will elevate fire concerns across the state on Sunday. Some tweaks have been made to winds on Friday and Saturday with this afternoon's forecast updates, but the overall forecast philosophy remains in tact.
From Monday onward, expect a subtle increase in shower trends to return to the islands as a combination of troughing aloft moves over the region. Trades will also return to the moderate to locally breezy range early next week.

Aviation

Moderate to locally breezy trades will continue through Friday. Showers will favor windward and mauka areas, with a slight uptick during the overnight and early morning hours. Expect mainly VFR, with brief MVFR under passing showers.
AIRMET Sierra for mountain obscurations remains in effect for windward sections of Oahu and the Big Island. Conditions should improve later tonight as drier air starts to move in.

Marine

High pressure north of Hawaii will slowly move eastward and drive moderate to locally strong trades across the local waters for the next couple of days. The Small Craft Advisory (SCA) for typically windier waters and channels near Maui and the Big Island has been extended through Saturday afternoon. Trade winds are forecast to increase further this weekend as the high strengthens, with potentially more widespread SCA conditions later this weekend into early next week. Trade wind speeds could then decrease slightly by middle of next week.
A small, long-period, south swell will gradually drop Friday into the weekend, with south shore surf slowly dropping as well. Back to back pulses of slightly larger south swells are possible starting Monday which could build surf near to above advisory levels (10 ft) along south facing shores as early as Monday night into Tuesday,then remain near to above average through much of next week.
Rough and choppy conditions will continue along east facing shores and may pick up further into early next week as winds strengthen. Surf will remain nearly flat along north facing shores.

HFO Watches/Warnings/Advisories

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

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Data Courtesy of NOAA.gov