Hilo

Tonight: Mostly cloudy with scattered showers. Lows 59 to 66 near the shore to 47 to 53 at 4000 feet. West winds up to 10 mph. Chance of rain 50 percent.

Friday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs around 79 near the shore to around 66 at 4000 feet. South winds up to 15 mph. Chance of rain 40 percent.

Friday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy after midnight. Lows 58 to 67 near the shore to 47 to 54 at 4000 feet. South winds up to 10 mph in the evening becoming light. Chance of rain 30 percent.

Kona

Tonight: Mostly clear. Haze. Lows around 69 near the shore to 40 to 48 near 5000 feet. Light winds.

Friday: Mostly sunny. Haze through the day. Isolated showers in the afternoon. Highs around 83 near the shore to around 65 near 5000 feet. West winds up to 10 mph. Chance of rain 20 percent.

Friday Night: Partly cloudy. Lows around 69 near the shore to 42 to 48 near 5000 feet. Light winds.

Waimea

Tonight: Partly cloudy with isolated showers. Lows 59 to 68 near the shore to 49 to 58 near 3000 feet. Southeast winds up to 15 mph. Chance of rain 20 percent.

Friday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Haze through the day. Highs around 78 near the shore to 69 to 75 near 3000 feet. South winds up to 10 mph shifting to the southeast in the afternoon. Chance of rain 50 percent.

Friday Night: Partly cloudy. Isolated showers in the evening. Lows 59 to 67 near the shore to 51 to 58 near 3000 feet. Light winds. Chance of rain 20 percent.

Kohala

Tonight: Partly cloudy with isolated showers. Lows 59 to 68 near the shore to 49 to 58 near 3000 feet. Southeast winds up to 15 mph. Chance of rain 20 percent.

Friday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Haze through the day. Highs around 78 near the shore to 69 to 75 near 3000 feet. South winds up to 10 mph shifting to the southeast in the afternoon. Chance of rain 50 percent.

Friday Night: Partly cloudy. Isolated showers in the evening. Lows 59 to 67 near the shore to 51 to 58 near 3000 feet. Light winds. Chance of rain 20 percent.

South Big Island

Tonight: Mostly clear. Breezy and haze. Lows around 70 near the shore to around 48 near 5000 feet. Northeast winds up to 20 mph becoming 10 to 15 mph after midnight.

Friday: Mostly sunny. Breezy. Haze through the day. Isolated showers in the afternoon. Highs around 83 near the shore to around 66 near 5000 feet. Northeast winds 10 to 20 mph shifting to the east up to 20 mph in the afternoon. Chance of rain 20 percent.

Friday Night: Partly cloudy. Lows around 70 near the shore to around 49 near 5000 feet. Northeast winds up to 15 mph.

Puna

Tonight: Mostly cloudy with scattered showers. Lows 59 to 66 near the shore to 47 to 53 at 4000 feet. West winds up to 10 mph. Chance of rain 50 percent.

Friday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs around 79 near the shore to around 66 at 4000 feet. South winds up to 15 mph. Chance of rain 40 percent.

Friday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy after midnight. Lows 58 to 67 near the shore to 47 to 54 at 4000 feet. South winds up to 10 mph in the evening becoming light. Chance of rain 30 percent.

Waikoloa

Tonight: Mostly clear. Haze. Lows 66 to 72 near the shore to 43 to 50 above 4000 feet. Southeast winds up to 15 mph.

Friday: Mostly sunny. Haze through the day. Isolated showers in the afternoon. Highs 80 to 85 near the shore to 62 to 69 above 4000 feet. South winds up to 10 mph shifting to the west in the afternoon. Chance of rain 20 percent.

Friday Night: Partly cloudy. Lows 66 to 72 near the shore to 44 to 51 above 4000 feet. Southeast winds up to 10 mph.

Detailed Forecast

Synopsis

Moderate to locally breezy trade winds will weaken tonight into Friday as a front approaches and stalls to the northwest. Overnight land breezes and afternoon sea breezes will prevail from Friday through early next week with the weak background flow becoming more southerly. A cold front may move over portions of the state by mid week next week and bring beneficial rain and breezy winds.

Discussion

Current radar and satellite imagery show a few clouds and isolated showers moving into windward areas on the moderate to breezy trades this evening, with a slight focus over the eastern end of the state, where a higher concentration of moisture can be seen upstream. This fairly limited windward shower activity will continue overnight.
Trades will begin to weaken and veer southeast tonight into tomorrow in response to an approaching weak cold front from the northwest. This will allow for a hybrid pattern to emerge tomorrow with some limited windward showers riding in on the weakening trades and some isolated sea breeze activity over the more wind-protected leeward areas. Then as the front inches closer and stalls north of the state this weekend, trades will continue to weaken and veer south and then eventually southwesterly across the western end of the island chain. During this period, land and sea breeze activity will become more widespread, allowing limited cloud and shower development over leeward and interior areas during the day and clearing at night.
Model guidance has been consistently showing that an upper level trough will dive down and sweep across the central Pacific and finally help to drive the next front through at least a portion of the island chain by mid week next week. As the southwesterly flow strengthens across the western half of the state late this weekend into early next week in advance of this front, this may overcome the land and sea breeze pattern for Kauai and Oahu and focus clouds and showers over leeward areas…especially if any prefrontal convergence bands materialize in the southwesterly flow. The latest global model runs look to have come into slightly better agreement on the timing of this front, bringing it to Kauai's doorstep on Tuesday evening, then slowly moving through the middle of the island chain by Wednesday evening before it stalls. This frontal passage looks to bring some beneficial rain to the area, along with breezy north-northeasterly winds for the western half of the state. Convergence along this dissipating frontal boundary, an abundance of upstream moisture, and a new plume of moisture associated with a low level disturbance moving towards the eastern end of the state will keep rain chances in the picture through the latter part of the week.
Finally, a hot spot over Halemaumau Crater on the Big Island continues to be seen on infrared satellite imagery. The University of Hawaii Vog Model shows that SO2 emissions should remain confined to portions of the Big Island and adjacent waters to the west and southwest through tomorrow morning. Then, assuming constant SO2 emissions, vog could begin to increase across some of the smaller islands by tomorrow night as background flow becomes more southerly.

Aviation

Trade winds will ease and shift out of the east-southeast tonight and Friday. This will allow for the development of overnight land breezes and daytime sea breezes in most areas across the state. Showers will favor windward areas tonight and early Friday, with a few showers possible over the island interiors Friday afternoon.
No AIRMETs are currently in effect.

Marine

No changes to the marine forecast this evening. The forecast remains on track. A ridge to the north of the islands will maintain moderate to fresh trade winds overnight. The ridge will sink southwards over the islands as a front to the northwest pushes east. Expect winds to decline Friday, and then shift to southerlies Saturday through early next week. The ridge is expected to move over Kauai Friday night, and then down the island chain through Sunday. This will bring gentle to locally moderate southwest winds north of the ridge and southeast winds south of the ridge. The approaching front is expected to produce increased southwest winds around Kauai and Oahu early next week, and the front may reach Kauai as early as Tuesday night. The front will bring the chance for thunderstorms to the northern offshore waters Saturday night through Tuesday.
Low end high surf conditions are expected along most north and west shores from Kauai to Maui through early Friday morning. The current northwest swell has been holding around 8 to 9 feet at 14 seconds at the NOAA buoys northwest of Kauai since last night, and are currently just a touch above guidance. The nearshore PacIOOS buoys have been ranging between 6 and 8 feet since Thursday morning. The models show a gradual decline overnight, and we expect surf to drop below High Surf Advisory thresholds by Friday morning.
A series of large to potentially extra large northwest swells is due this weekend and next week. A large, very intense low formed in the northwest Pacific yesterday and is producing an elongated fetch pointed toward the islands. Long period forerunners of the swell will build through Saturday, and surf along north and west shores, including leeward Big Island, should far exceed High Surf Warning thresholds during the peak of the swell Saturday night into Sunday. A Small Craft Advisory (SCA) will also be needed for seas in excess of 10 ft for waters exposed to the swell. The large northwest Pacific gyre will send additional pulses of large to potentially extra large swell Monday night through Wednesday.
Surf along east and south facing shores will remain small through the week.

Fire weather

No critical fire weather conditions are expected for the next seven days. Moderate to locally breezy trade winds will gradually ease late tonight into Friday. A daytime sea breeze and overnight land breeze pattern will develop Friday into early next week as a weak southerly background flow takes over. Relative humidities will stay above critical levels through the forecast period. An approaching front has the potential to move through the state from mid- to late week next week, providing much needed rainfall to leeward locations.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Friday for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala.

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Data Courtesy of NOAA.gov