Hilo

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 65 to 73 near the shore to 56 to 61 at 4000 feet. North winds up to 15 mph. Chance of rain 70 percent.

Sunday: Mostly cloudy with numerous showers. Highs 80 to 88 near the shore to around 69 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Sunday Night: Mostly cloudy with numerous showers. Lows 65 to 73 near the shore to 55 to 61 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 70 percent.

Kona

Tonight: Partly cloudy with isolated showers. Lows around 76 near the shore to 51 to 57 near 5000 feet. Light winds. Chance of rain 20 percent.

Sunday: Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 85 to 90 near the shore to 67 to 72 near 5000 feet. West winds up to 10 mph. Chance of rain 20 percent.

Sunday Night: Mostly cloudy with scattered showers in the evening, then mostly clear after midnight. Lows 73 to 78 near the shore to 51 to 57 near 5000 feet. Light winds. Chance of rain 40 percent.

Waimea

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 65 to 73 near the shore to 57 to 64 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Sunday: Breezy. Partly sunny with scattered showers. Highs 65 to 87. East winds 10 to 20 mph. Chance of rain 50 percent.

Sunday Night: Mostly cloudy with scattered showers. Lows 65 to 73 near the shore to 57 to 64 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Kohala

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 65 to 73 near the shore to 57 to 64 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Sunday: Breezy. Partly sunny with scattered showers. Highs 65 to 87. East winds 10 to 20 mph. Chance of rain 50 percent.

Sunday Night: Mostly cloudy with scattered showers. Lows 65 to 73 near the shore to 57 to 64 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

South Big Island

Tonight: Mostly clear. Breezy. Lows around 75 near the shore to around 54 near 5000 feet. Northeast winds up to 20 mph.

Sunday: Breezy. Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 87 near the shore to around 70 near 5000 feet. East winds up to 20 mph. Chance of rain 30 percent.

Sunday Night: Mostly cloudy with isolated showers in the evening, then mostly clear after midnight. Lows around 75 near the shore to around 54 near 5000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Puna

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 65 to 73 near the shore to 56 to 61 at 4000 feet. North winds up to 15 mph. Chance of rain 70 percent.

Sunday: Mostly cloudy with numerous showers. Highs 80 to 88 near the shore to around 69 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Sunday Night: Mostly cloudy with numerous showers. Lows 65 to 73 near the shore to 55 to 61 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 70 percent.

Waikoloa

Tonight: Mostly clear. Breezy. Lows around 77 near the shore to 53 to 58 above 4000 feet. East winds up to 20 mph.

Sunday: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs 85 to 91 near the shore to 67 to 75 above 4000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

Sunday Night: Partly cloudy. Isolated showers in the evening. Lows around 77 near the shore to 53 to 58 above 4000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Stable conditions and gentle to breezy trade winds will prevail through much of next week, with a brief weakening in wind speeds Monday through Tuesday. An area of increased moisture passing from east to west through the state could give a slight boost to windward showers Sunday through Monday night.

Discussion

Visible satellite and radar imagery show a few bands of unstable clouds and scattered showers stretched upstream of the state, mostly aimed toward windward and mountain areas of the Big Island and Maui County this afternoon. Stable conditions have kept rain amounts very light today. The western end of the state is dominated by scattered stable clouds and drier conditions. The 00Z upper air soundings from Lihue and Hilo still show temperature inversion heights in the 5,000 to 7,000 foot range with precipitable water values running slightly above average for August. Surface high pressure far north of the state will continue to drive gentle to breezy trade winds across the islands with mainly scattered windward and mauka showers state-wide for the next couple of days.
A slight change in weather conditions will occur Sunday through Monday night, as a weak tropical wave passes from east to west to the south of the islands. Low-level forcing from this feature will lift temperature inversion heights into the 6,000 to 8,000 foot range and help drag an area of increased precipitable water through through the islands, allowing for more unstable clouds and increasing shower trends. The best chances for enhanced shower activity will be over the windward and mountain areas Sunday and Monday nights/early mornings. Some of the stronger showers may move into the typically drier leeward locations at times. A brief drop in the trade wind speeds remains in the forecast for Monday and Monday night as a passing front near the Aleutians briefly displaces the high north of Hawaii off to the east a bit.
Global models indicate a fairly stable, moderate to locally breezy trade wind weather pattern prevailing through much of the rest of the week. However, there remains a large degree of uncertainty in the wind and weather patterns heading into next weekend due to potential tropical cyclone activity in the Central Pacific, east of Hawaii. The National Hurricane Center is forecasting a high chance of tropical cyclone development in the East Pacific over the next seven days with westward movement into the Central Pacific by the end of next week. However, the GFS and ECMWF long-range model guidance differ significantly in the existence, position, and strength of activity near Hawaii. Specific island forecast details from Friday onward will highly depend upon this potential tropical development.

Aviation

Latest satellite and radar imagery this afternoon shows that many of the low clouds and showers that were moving into windward sections of the islands earlier today have now dissipated. Therefore, AIRMET Sierra has been cancelled for all islands. However, moisture embedded within breezy trade winds will allow clouds and showers to favor N through SE sections of the islands at times for the next several days, particularly during the overnight to early morning hours each day. Otherwise, VFR conditions should generally prevail.
AIRMET Tango for low level turbulence leeward of the terrain is in effect statewide due to the breezy trades. This AIRMET will likely be needed into early next week.

Marine

An area of strong high pressure centered approximately 1,300 nm north northeast of Oahu is pressing down a tight enough pressure gradient over the local waters to maintain moderate to locally strong trade winds this weekend. A Small Craft Advisory is in effect for the typical windier waters around Maui County and Big Island through Sunday afternoon.
The ongoing small south swell will further decline into the evening with a small southeastern pulse lingering through tonight. A moderate size, longer period more due south swell will arrive late Sunday and fill in early Monday, slowly falling off through the middle of next week. Seasonally flat to very small north-facing shore surf is expected through early next week. There is a possibility of a mid week arrival of a small, long period northwest swell originating from Typhoon Ampil currently located a few hundred miles east of northern Japan. East shore surf will remain somewhat elevated the next few days in response to stronger trade flow.
The combination of a full moon Monday and water levels running around a half a foot higher than predicted could produce minor coastal flooding during afternoon high tides the next couple of days.

HFO Watches/Warnings/Advisories

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

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Data Courtesy of NOAA.gov