Hilo

Tonight: Mostly cloudy with scattered showers. Lows 65 to 72 near the shore to 53 to 59 at 4000 feet. Northwest winds up to 15 mph. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers. Highs 80 to 87 near the shore to 67 to 72 at 4000 feet. Northeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers. Lows 66 to 72 near the shore to 54 to 61 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Kona

Tonight: Mostly cloudy with isolated showers in the evening, then mostly clear after midnight. Lows 71 to 76 near the shore to 50 to 55 near 5000 feet. Light winds. Chance of rain 20 percent.

Friday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs around 87 near the shore to around 72 near 5000 feet. West winds up to 10 mph. Chance of rain 20 percent.

Friday Night: Partly cloudy. Isolated showers in the evening. Lows around 74 near the shore to 50 to 56 near 5000 feet. North winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Waimea

Tonight: Breezy. Partly cloudy with isolated showers. Lows 64 to 72 near the shore to 56 to 63 near 3000 feet. East winds up to 25 mph with gusts to 45 mph. Chance of rain 20 percent.

Friday: Mostly sunny. Windy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 64 to 86. East winds up to 30 mph increasing to 10 to 30 mph in the afternoon. Chance of rain 50 percent.

Friday Night: Windy. Partly cloudy with isolated showers. Lows 65 to 72 near the shore to 57 to 64 near 3000 feet. East winds 10 to 30 mph. Chance of rain 20 percent.

Kohala

Tonight: Breezy. Partly cloudy with isolated showers. Lows 64 to 72 near the shore to 56 to 63 near 3000 feet. East winds up to 25 mph with gusts to 45 mph. Chance of rain 20 percent.

Friday: Mostly sunny. Windy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 64 to 86. East winds up to 30 mph increasing to 10 to 30 mph in the afternoon. Chance of rain 50 percent.

Friday Night: Windy. Partly cloudy with isolated showers. Lows 65 to 72 near the shore to 57 to 64 near 3000 feet. East winds 10 to 30 mph. Chance of rain 20 percent.

South Big Island

Tonight: Mostly clear. Windy. Lows around 75 near the shore to around 57 near 5000 feet. Northeast winds up to 30 mph.

Friday: Mostly sunny. Windy. Isolated showers in the afternoon. Highs around 88 near the shore to around 72 near 5000 feet. East winds up to 35 mph. Chance of rain 20 percent.

Friday Night: Mostly clear. Windy. Lows around 75 near the shore to around 57 near 5000 feet. Northeast winds 10 to 30 mph.

Puna

Tonight: Mostly cloudy with scattered showers. Lows 65 to 72 near the shore to 53 to 59 at 4000 feet. Northwest winds up to 15 mph. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers. Highs 80 to 87 near the shore to 67 to 72 at 4000 feet. Northeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers. Lows 66 to 72 near the shore to 54 to 61 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Waikoloa

Tonight: Mostly clear. Breezy. Lows around 75 near the shore to 52 to 57 above 4000 feet. Southeast winds up to 25 mph.

Friday: Sunny and windy. Isolated showers in the afternoon. Highs 84 to 91 near the shore to 68 to 76 above 4000 feet. Northeast winds up to 30 mph with gusts to 50 mph. Chance of rain 20 percent.

Friday Night: Mostly clear. Breezy. Lows around 76 near the shore to 53 to 58 above 4000 feet. Northeast winds up to 25 mph. Gusts up to 50 mph in the evening.

Detailed Forecast

Synopsis

Breezy to locally windy trades and rather dry and stable conditions will persist through Friday and likely Saturday. Clouds and light showers will be focused over windward and mauka areas, while most leeward areas remain dry. Stable trade winds will gradually ease Sunday through Tuesday.

Discussion

A gusty, stable, and rather dry trade wind flow is in place. Even though the surface high far north of Hawaii is not exceptionally strong, activity in the tropics south of Hawaii is producing a somewhat tight pressure gradient over the region. In addition, a ridge aloft overhead is producing an inversion based between roughly 5,000 to 6,000 feet. Under these very stable conditions, trades are being accelerated over and downwind of terrain, and winds are strong enough to require a Wind Advisory over portions of Maui County and the Big Island. Shallow pockets of moisture moving along the trade wind flow have led to only light rainfall accumulation along windward slopes and dry weather leeward.
Little change is expected on Friday and likely Saturday. The surface high north of the state will strengthen slightly as it drifts eastward, and a surface trough in the deep tropics will pass south of the islands, keeping the pressure gradient rather tight. The Wind Advisory runs through Friday afternoon, and depending on how quickly the surface trough to the south moves westward, winds may hold around current strength through Saturday. Modest showers will remain confined to windward areas.
Trade winds will gradually decline Sunday into Tuesday as the high drifts eastward and the local pressure gradient slowly relaxes. The stable pattern of mainly windward and mauka showers should persist as little organized moisture is depicted in the guidance.
Some uncertainty is introduced by the middle of next week. The latest National Hurricane Center forecast depicts current east Pacific Tropical Storm Gil weakening to a remnant low well east of Hawaii early next week, and the GFS and ECMWF show a remnant circulation passing near the state around Wednesday or so. It's too early to determine what, if any effects, this feature will bring for island weather.

Aviation

Breezy to windy trade winds will persist through tomorrow and allow for prevailing VFR conditions. MVFR conditions may occur with passing showers over windward and mountain areas, especially overnight and in the early morning hours.
AIRMET Tango is in effect for moderate with isolated severe turbulence over and immediately S through W of the island mountains due to breezy trade winds and recent reports of severe turbulence.

Marine

High pressure far northeast of the state will help generate fresh to locally near gale trades through the weekend. A Small Craft Advisory (SCA) is in effect for most marine zones surrounding Maui and the Big Island and has been extended through Friday night. Additional zones may need to be added to the SCA this weekend due to increasing winds as the high pressure to the north strengthens. Trades then begin to weaken early next week as the aforementioned high drifts further east.
Tropical Storm Iona continues to track to the west, far west- southwest of the main Hawaiian Islands. Additional tropical cyclone development is possible far south-southeast of Hawaii over the next day or so, but expecting little to no impact on our local waters.
A long period south swell continues to filter into our local waters this afternoon and is expected to peak late today through tomorrow, then slowly decline thereafter. A High Surf Advisory remains in effect for the south facing shores of all islands through tomorrow afternoon. This first south swell event will be followed by another long period south swell early next week.
East shore surf will remain elevated and choppy due to locally strong trade winds through this weekend. This will be followed by a decline early next week as trades weaken.
Flat summer conditions along north facing shores may be interrupted late this weekend by a small long period northwest swell from Tropical Storm Krosa, currently in the western Pacific.

Fire weather

A gusty, stable, and rather dry trade wind flow will remain in place through Friday and likely into Saturday. Critical fire weather conditions, with winds of 20 mph or more and daytime relative humidity of 35 to 45 percent, is expected to persist over leeward areas through Friday afternoon, and possibly into Saturday. A strong inversion based around 5,000 feet will ensure that higher elevations of the Big Island and Haleakala on Maui experience very low relative humidity. Winds will decline Sunday into Tuesday, lowering fire weather concerns.

HFO Watches/Warnings/Advisories

Red Flag Warning until 6 PM HST Friday for Niihau, Kauai South, Kauai Southwest, East Honolulu, Honolulu Metro, Ewa Plain, Waianae Coast, Oahu North Shore, Central Oahu, Waianae Mountains, Molokai North, Molokai West, Molokai Leeward South, Lanai Windward, Lanai Leeward, Lanai South, Lanai Mauka, Kahoolawe, Maui Leeward West, Maui Central Valley North, Maui Central Valley South, South Maui/Upcountry, South Haleakala, Big Island South, Big Island Southeast, Kohala, Big Island Interior.
High Surf Advisory until 6 PM HST Friday for Niihau, Kauai Leeward, Waianae Coast, Kahoolawe, Maui Leeward West, Kona, Kauai South, East Honolulu, Honolulu Metro, Ewa Plain, Molokai Southeast, Molokai Leeward South, Lanai Leeward, Lanai South, Maui Central Valley South, Kipahulu, South Maui/Upcountry, South Haleakala, Big Island South, Big Island Southeast.
Wind Advisory until 6 PM HST Friday for Lanai Mauka, Kahoolawe, Kohala, Lanai Windward, Lanai Leeward, Maui Central Valley North, Maui Central Valley South, Big Island South, Big Island Southeast, Big Island North.
Small Craft Advisory until 6 AM HST Saturday for Kaiwi Channel, Maui County Windward Waters, Maalaea Bay, 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