Hilo

Tonight: Breezy. Mostly cloudy with showers. Lows 61 to 69 near the shore to 50 to 57 at 4000 feet. East winds up to 20 mph. Chance of rain 80 percent.

Saturday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 78 to 83 near the shore to 61 to 66 at 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Saturday Night: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 60 to 69 near the shore to 49 to 56 at 4000 feet. North winds up to 10 mph shifting to the west after midnight. Chance of rain 20 percent.

Kona

Tonight: Partly cloudy. Lows around 72 near the shore to 48 to 54 near 5000 feet. West winds up to 10 mph shifting to the east after midnight. Gusts up to 30 mph.

Saturday: Partly sunny in the morning, then mostly sunny with scattered showers in the afternoon. Highs 82 to 88 near the shore to around 66 near 5000 feet. South winds up to 10 mph in the morning becoming light. Chance of rain 40 percent.

Saturday Night: Partly cloudy. Lows around 71 near the shore to 47 to 52 near 5000 feet. Light winds.

Waimea

Tonight: Windy. Partly cloudy with scattered showers. Lows 61 to 71 near the shore to 55 to 62 near 3000 feet. East winds up to 30 mph with gusts to 50 mph decreasing to up to 20 mph after midnight. Chance of rain 50 percent.

Saturday: Partly sunny with isolated showers in the morning, then mostly sunny in the afternoon. Highs around 79 near the shore to 66 to 78 near 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Saturday Night: Partly cloudy with isolated showers. Lows 61 to 70 near the shore to 54 to 61 near 3000 feet. East winds up to 15 mph becoming around 10 mph after midnight. Chance of rain 20 percent.

Kohala

Tonight: Windy. Partly cloudy with scattered showers. Lows 61 to 71 near the shore to 55 to 62 near 3000 feet. East winds up to 30 mph with gusts to 50 mph decreasing to up to 20 mph after midnight. Chance of rain 50 percent.

Saturday: Partly sunny with isolated showers in the morning, then mostly sunny in the afternoon. Highs around 79 near the shore to 66 to 78 near 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Saturday Night: Partly cloudy with isolated showers. Lows 61 to 70 near the shore to 54 to 61 near 3000 feet. East winds up to 15 mph becoming around 10 mph after midnight. Chance of rain 20 percent.

South Big Island

Tonight: Windy. Partly cloudy with scattered showers. Lows around 74 near the shore to around 54 near 5000 feet. East winds 15 to 35 mph shifting to the northeast up to 35 mph after midnight. Gusts up to 55 mph. Chance of rain 50 percent.

Saturday: Mostly sunny. Breezy. Scattered showers in the afternoon. Highs around 85 near the shore to around 65 near 5000 feet. East winds up to 25 mph. Chance of rain 40 percent.

Saturday Night: Mostly clear. Breezy. Lows around 73 near the shore to around 53 near 5000 feet. Northeast winds up to 25 mph becoming 10 to 20 mph after midnight.

Puna

Tonight: Breezy. Mostly cloudy with showers. Lows 61 to 69 near the shore to 50 to 57 at 4000 feet. East winds up to 20 mph. Chance of rain 80 percent.

Saturday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 78 to 83 near the shore to 61 to 66 at 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Saturday Night: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 60 to 69 near the shore to 49 to 56 at 4000 feet. North winds up to 10 mph shifting to the west after midnight. Chance of rain 20 percent.

Waikoloa

Tonight: Partly cloudy. Windy. Lows around 73 near the shore to 50 to 55 above 4000 feet. Northeast winds up to 35 mph with gusts to 60 mph shifting to the east up to 25 mph after midnight.

Saturday: Mostly sunny. Highs around 85 near the shore to 64 to 70 above 4000 feet. North winds up to 15 mph.

Saturday Night: Mostly clear. Lows 69 to 74 near the shore to 49 to 54 above 4000 feet. East winds up to 15 mph.

Detailed Forecast

Synopsis

Locally breezy trades continue into the weekend during which time drier weather is anticipated. There is a chance for a brief period of wetter weather during the middle of next week.

Discussion

A drier pattern has already established over the western end of the island chain where partly cloudy skies and limited shower activity prevail. Visible imagery suggests a narrow ribbon of even drier air lurking immediately upstream as evidenced by nearly cloud free skies east of the islands. As this drier airmass advances into the area, it will cause steady showers over Windward Big Island & Maui to gradually diminish as the night progresses. The smaller islands will likewise remain mostly dry through the night. Locally breezy trades and a fairly typical trade wind pattern then prevail through at least Monday.
Global guidance in good agreement this afternoon that a rather warm closed low will develop in situ over the islands during the early portion of next week. Attendant adjustment to the low-level wind field will cause emerging SE winds in the mid-levels to advect deep tropical moisture over the area with PWATs modeled to be in excess of 1.5″ as early as Monday while ESE trades prevail at the surface. PWATs eventually modeled to reach or exceed 2″ areawide by late Tuesday or Wednesday. Forecast soundings and model cross sections indicate rather dry and stable low-levels inititally which suggests potential for some higher based light/stratiform rain operating independently of trade wind showers below during the initial moisture surge. However, as moisture deepens during mid-week, the potential will exist for any moisture embedded in the trades to capitalize on existing convective instability and also tap into ample mid/upper level moisture suggesting a brief window for moderate to heavy, but still progressive, trade wind showers. The best opportunity for such shower activity likely comes as the aforementioned closed low deamplifies and lifts NE out of the area bringing with it a brief hit of dynamic forcing Tues into Wed. Worth noting that the GFS has demonstrated a tendency to spin up a spurious low out of grid scale convection SE of the Big Island. Subsequent output of heavy indicating associated heavy rain and strong wind field are likely unreliable for now. Potential for flooding in this scenario appears limited at this time but bears monitoring in subsequent forecast cycles.

Aviation

Breezy trade winds will begin to gradually ease tonight and into tomorrow. Showers are continuing to impact windward and mountainous areas, especially over the Big Island. MVFR conditions prevail over windward sections of the Big Island, with brief isolated IFR conditions possible through tonight. Occasional MVFR conditions are possible over windward and mountainous areas elsewhere across the state. Otherwise, VFR will prevail.
AIRMET Sierra remains in effect for windward Big Island. This will likely continue through tonight due to upstream clouds and showers.
AIRMET Tango remains in effect for moderate low-level turbulence over and downwind of island terrain below 10,000 feet. This is expected to remain at least through the evening, and will likely be adjusted tomorrow due to winds gradually easing across the state.

Marine

Strong high pressure to the NE will weaken and move SE over the weekend. Moderate to strong easterly trade winds will decrease to locally strong this weekend as the high weakens. A Small Craft Advisory (SCA) is in effect through this afternoon for both gusty winds and high seas. Western marine zones will fall off tonight with zones from the Kaiwi Channel eastward remaining in the SCA overnight Saturday morning. A SCA will be in effect for the traditionally windy waters surrounding Maui County and Big Island until 6 AM Sunday morning.
The forecast becomes uncertain next week as some guidance indicates a mid level trough moving over the islands from the southeast. This mid level trough, if actually occurs as depicted, could create a surface trough by Monday night, disrupt the trade winds, and allow for thunderstorms to develop across the local waters. Other model guidance suggests a weaker mid level trough with trade winds continuing through the first half of next week. Additionally, a cold front could approach the NW offshore waters by Tuesday evening.
Large short period northeast swell generated by a strong trade fetch will be on the gradual decline through the weekend as a result of weakening local and upstream trades. Large surf for east shores is possible by the middle of next week depending on the evolution of a potential surface trough and approaching cold front.
A small, medium period northwest swell will fill in late Saturday afternoon and provide a small boost to north and west-facing shores through the weekend. Small medium to long period west- northwest swells will then keep surf from going flat early next week. A moderate long period west northwest swell is possible next week and could bring advisory level surf to north and west shores by the middle of next week.
For south shores, small background southerly swell will remain through the weekend and into early next week.

Fire weather

The inversion slopes from around 7kft at Lihue to 10kft at Hilo per this afternoon's upper air observations. The inversion will fall to around 5 or 6kft by Saturday as drier air infiltrates the area and the resident band of showers over Windward Big Island sags south and diminishes. Seasonably cool temperatures will maintain elevated RH values even as dewpoints tumble a bit heading into Saturday. The potential exists for a brief period of wetter weather during the middle of next week.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Saturday for Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Big Island Windward Waters.
Small Craft Advisory until 6 AM HST Sunday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov