West Kaua’i

Today: Sunny. Isolated showers in the morning. Highs 87 to 92 near the shore to around 78 above 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Lows 71 to 76 near the shore to around 63 above 3000 feet. East winds 10 to 15 mph.

Sunday: Sunny. Highs 87 to 92 near the shore to around 78 above 3000 feet. East winds 10 to 15 mph.

South Kaua’i

Today: Mostly sunny. Breezy. Isolated showers in the morning. Highs 82 to 90. East winds 15 to 20 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Breezy. Isolated showers after midnight. Lows around 75. Northeast winds 15 to 20 mph. Chance of rain 20 percent.

Sunday: Mostly sunny. Isolated showers in the morning. Highs 82 to 90. Northeast winds around 15 mph. Chance of rain 20 percent.

Kaua’i Mountains

Today: Breezy. Partly sunny with numerous showers in the morning, then mostly sunny with scattered showers in the afternoon. Highs 75 to 85 in the valleys to around 68 above 4000 feet. East winds 15 to 20 mph. Chance of rain 70 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Breezy. 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.

Sunday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 76 to 85 in the valleys to around 68 above 4000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

North Kaua’i

Today: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 78 to 88. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers. Lows 66 to 75. East winds 10 to 15 mph. Chance of rain 20 percent.

Sunday: Mostly sunny. Isolated showers in the morning. Highs 78 to 88. East winds 10 to 15 mph. Chance of rain 20 percent.

East Kaua’i

Today: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 74 to 87. East winds around 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers. Lows 67 to 78. Northeast winds around 15 mph. Chance of rain 20 percent.

Sunday: Mostly sunny with isolated showers. Highs 75 to 87. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Breezy to locally windy trades and rather dry and stable conditions will continue today. Clouds and light showers being carried in on the trade wind flow will remain focused over windward and mauka areas, while most leeward areas will remain dry. Stable trade winds will gradually ease Sunday through Tuesday and may become disrupted Wednesday or Thursday.

Discussion

No change to the forecast or forecast philosophy this morning. High pressure to the north and northeast, and low pressure to the south, combined with high pressure aloft, remain the driving force behind our weather.
This combination has tightened the pressure gradient over the islands leading to a gusty, stable and relatively dry trade wind flow that will continue today. The inversion is between 5,000 to 6,500 feet, and the resulting stability will continue to produce localized strong winds near terrain across the Kohala Districts of the Big Island and the central valley of Maui, where the Wind Advisory continue through this afternoon. Shallow pockets of moisture being carried in on the trade wind flow will continue to bring light rainfall accumulation mainly to windward slopes, with leeward areas remaining dry.
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, essentially typical August rainfall, should persist as little organized moisture is depicted in the guidance.
Trades will likely become disrupted Wednesday or Thursday, though there is uncertainty in the details. 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 north or near the state as early as Wednesday but potentially Thursday. Disrupted trades is the most likely scenario, but it's too early to know if there will be any significant chance for enhanced rainfall.

Aviation

High pressure far north and northeast of the islands, combined with a low pressure system to the southwest, will maintain breezy to windy trade winds into the weekend. VFR conditions are expected to prevail, however some passing showers could bring brief MVFR conditions mainly to 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 strong trade winds and gusts.

Marine

High pressure will remain far north of the state this weekend and help generate fresh to locally strong trades across the local waters. A Small Craft Advisory (SCA) remains in effect through tonight for most marine zones surrounding Maui and the Big Island, then limited to the typical windier zones through Sunday as trades begin to ease. Trades will continue to weaken through mid next week as the aforementioned high drifts further east.
South swell energy has shown signs of a slow decline this morning, noted on the Lanai nearshore buoy, both in magnitude and period. By mid-morning, the remaining 4 foot moderate period swell will likely be generating elevated surf along south facing shores, just shy of advisory criteria. Thus, the High Surf Advisory has been canceled. Another moderate, long period, south swell is poised to arrive late Sunday into Monday, once again building surf to near advisory levels.
East shore surf will remain elevated and choppy through Sunday morning due to locally strong trade winds, then lower slightly as trades begin to slowly ease late Sunday and beyond.
Nearly flat conditions will prevail along north facing shores through tonight. A small long period northwest swell, originating from Typhoon Krosa in the western Pacific, will bring a small bump up in surf along north facing shores Sunday into early next week.

Fire weather

A gusty, stable, and rather dry trade wind flow will remain in place today, producing critical fire weather conditions, with winds of 20 mph or more and daytime relative humidity of 35 to 45 percent. A strong inversion based between 5,000 to 6,500 feet will ensure that higher elevations of the Big Island and portions of 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 this evening 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.
Wind Advisory until 6 PM HST this evening for Kohala, Maui Central Valley North, Maui Central Valley South, Big Island North.
Small Craft Advisory until 6 PM HST this evening for Kaiwi Channel, Maui County Windward Waters, Big Island Windward Waters.
Small Craft Advisory until 6 PM HST Sunday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.