West Kaua’i

Tonight: Mostly clear. Breezy. Lows 71 to 76 near the shore to around 63 above 3000 feet. Northeast winds up to 20 mph.

Friday: Sunny and breezy. Highs 86 to 92 near the shore to around 78 above 3000 feet. East winds up to 25 mph.

Friday Night: Mostly clear. Lows 71 to 76 near the shore to around 64 above 3000 feet. East winds 10 to 15 mph.

South Kaua’i

Tonight: Breezy. Partly cloudy with isolated showers. Lows around 75. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Friday: Breezy. Mostly sunny with isolated showers. Highs 81 to 90. Northeast winds 15 to 25 mph. Chance of rain 20 percent.

Friday Night: Partly cloudy with isolated showers. Lows around 75. Northeast winds around 15 mph. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Scattered showers. Lows 66 to 71 in the valleys to around 60 above 4000 feet. East winds 10 to 20 mph decreasing to up to 20 mph after midnight. Chance of rain 50 percent.

Friday: Mostly sunny in the morning then becoming partly sunny. Breezy. Scattered showers. Highs 75 to 85 in the valleys to around 68 above 4000 feet. East winds 10 to 20 mph. Chance of rain 40 percent.

Friday Night: Breezy. Mostly cloudy with scattered showers. Lows 66 to 71 in the valleys to around 61 above 4000 feet. East winds 15 to 20 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 66 to 75. East winds up to 15 mph shifting to the southeast after midnight. Chance of rain 40 percent.

Friday: Breezy. Mostly sunny with isolated showers. Highs 78 to 89. East winds up to 20 mph. Chance of rain 20 percent.

Friday Night: Partly cloudy with scattered showers. Lows 66 to 75. East winds 10 to 15 mph. Chance of rain 30 percent.

East Kaua’i

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 66 to 78. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Friday: Breezy. Mostly sunny with isolated showers. Highs 74 to 87. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Friday Night: Mostly cloudy with scattered showers. Lows 67 to 78. East winds around 15 mph. Chance of rain 50 percent.

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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