Hilo

Today: Mostly sunny with isolated showers. Highs 78 to 83 near the shore to 63 to 69 at 4000 feet. Southeast winds up to 10 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Lows 61 to 70 near the shore to around 56 at 4000 feet. South winds up to 10 mph.

Friday: Mostly sunny. Isolated showers in the afternoon. Highs 77 to 82 near the shore to 61 to 68 at 4000 feet. Southeast winds up to 10 mph. Chance of rain 20 percent.

Kona

Today: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 78 to 84 near the shore to around 66 near 5000 feet. Southwest winds up to 10 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy in the evening then becoming mostly clear. Isolated showers. Lows around 70 near the shore to 49 to 55 near 5000 feet. Light winds. Chance of rain 20 percent.

Friday: Sunny in the morning then becoming partly sunny. Isolated showers. Highs 78 to 84 near the shore to around 65 near 5000 feet. West winds up to 10 mph. Chance of rain 20 percent.

Waimea

Today: Mostly sunny with isolated showers. Highs around 77 near the shore to 67 to 74 near 3000 feet. Light winds. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 61 to 69 near the shore to 55 to 61 near 3000 feet. Light winds. Chance of rain 20 percent.

Friday: Mostly sunny. Isolated showers in the afternoon. Highs around 77 near the shore to 66 to 74 near 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Kohala

Today: Mostly sunny with isolated showers. Highs around 77 near the shore to 67 to 74 near 3000 feet. Light winds. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 61 to 69 near the shore to 55 to 61 near 3000 feet. Light winds. Chance of rain 20 percent.

Friday: Mostly sunny. Isolated showers in the afternoon. Highs around 77 near the shore to 66 to 74 near 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

South Big Island

Today: Sunny. Scattered showers in the afternoon. Highs around 80 near the shore to around 64 near 5000 feet. Southeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 30 percent.

Tonight: Mostly cloudy with isolated showers in the evening, then mostly clear after midnight. Lows around 72 near the shore to around 52 near 5000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Friday: Sunny. Isolated showers in the afternoon. Highs around 81 near the shore to around 64 near 5000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Puna

Today: Mostly sunny with isolated showers. Highs 78 to 83 near the shore to 63 to 69 at 4000 feet. Southeast winds up to 10 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Lows 61 to 70 near the shore to around 56 at 4000 feet. South winds up to 10 mph.

Friday: Mostly sunny. Isolated showers in the afternoon. Highs 77 to 82 near the shore to 61 to 68 at 4000 feet. Southeast winds up to 10 mph. Chance of rain 20 percent.

Waikoloa

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 78 to 83 near the shore to 62 to 67 above 4000 feet. West winds up to 10 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows around 71 near the shore to 50 to 55 above 4000 feet. Light winds. Chance of rain 20 percent.

Friday: Sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 78 to 84 near the shore to around 65 above 4000 feet. Northwest winds up to 10 mph. Chance of rain 40 percent.

Detailed Forecast

Synopsis

A surface trough will linger across Maui County into Friday, maintaining wet conditions over the central portion of the state. Light to moderate northeasterly trade winds and drier conditions will prevail over Kauai, while light east to southeast winds will produce mainly afternoon clouds and showers over leeward and interior Big Island. Moderate easterly trade winds will build across the entire state this weekend, bringing mainly windward showers.

Discussion

Conditions haven't changed all that much from the past 24 hours, with overnight satellite imagery continuing to show extensive low clouds over the central portion of the state as the weakening surface trough remains stalled over Maui County. The shallow moisture depth and weak east-northeast flow continue to focus shower activity along windward portions of Maui County and Oahu. Windward Oahu experienced the highest rainfall totals overnight, where additional rainfall amounts of one-half to just over an inch were observed at several sites. Cloud cover has dissipated over much of Kauai and the Big Island overnight as well due to land breeze development in the light winds there.
Little change is expected into Friday aside from a slight weakening of the northeast trade wind flow over the western half of the state. The surface trough will meander over Maui County, while a broad and weak mid to upper level trough maintains slight instability. The moisture associated with the surface trough will gradually become more diffuse over the next couple of days, but continue to focus most of the shower activity along windward Maui County and Oahu. Under this hybrid weak trade/variable wind pattern, sea breezes will drive afternoon and evening showers across leeward areas of these islands, as well as the Big Island, with showers tapering off at night. Light trades and drier conditions will hang on across Kauai.
The surface trough and its associated pool of moisture will dissipate late Friday through Saturday as surface high pressure passes north of the islands, bringing strengthening trade winds out of a more easterly direction. The remaining moisture may fuel active windward showers on Saturday, before a drier trade wind flow settles in for Sunday.
Uncertainty increases early next week. The latest GFS and ECMWF runs are coming into better agreement for more troughing at the surface and aloft near the islands during the first part of next week, which would turn the flow more southeasterly Tuesday and potentially light and variable over the western end of the state for Wednesday. However, significant differences in the strength and location of these features remain, so sticking with a blended approach for the time being. Regardless, expect east to southeast winds to maintain a pattern of mainly windward rainfall through at least Monday, with higher odds for wetter weather by the middle of next week.

Aviation

A nearly stationary surface trough over Maui County will continue to act as a focus for low cloud and shower development as it gradually weakens through tonight, with unusually low cloud bases. Widespread MVFR VIS/CIG and isolated pockets of IFR VIS/CIG in moderate showers can be expected over windward areas from Oahu to Maui County, where AIRMET Sierra is in effect for mountain obscuration.
Little change is expected with the trough and associated moisture through tonight as light to locally moderate trade winds prevail. Periods of broken low clouds are likely to occur over NE Kauai, with cloud bases generally above 030, but skies have cleared somewhat recently. Land breezes on the Big Island have to led to gradual overnight clearing, but the light winds will allow afternoon sea breezes to drive cloud and shower formation once again this afternoon. Leeward clouds/showers may increase over other islands as well due to sea breeze convergence this afternoon.

Marine

Moderate to locally fresh northeast winds will continue over the waters around the smaller islands today as a weak trough lingers over Maui County. Light to moderate east to southeast winds will hold east of this boundary over the Big Island waters. A return of fresh to locally strong easterly trades is forecast Friday through the weekend as high pressure builds north of the state. Looking ahead into next week, guidance continues to show the trades easing and veering out of the southeast as a potent upper trough dips southeastward toward the region. Although confidence in the details this far out remains low, a transition to a wetter pattern will become possible through the week for portions of the state.
Surf along exposed north and west facing shores will remain small through the weekend with mainly a mix of short to medium period north and northwest swells moving through. For the long range, guidance is showing a gale low that is beginning to emerge over the far northwest Pacific this morning tracking east-southeast Friday into the weekend. Gales associated with this system are shown locked in down the 300-320 degree directional band relative to the islands with seas within the fetch rising into the 25-35 ft range. If this materializes, a long-period northwest swell arriving locally next Monday would result. This source should peak Monday night through Tuesday night, then ease through midweek.
A fresh long-period south swell filling in this morning should lead to a slight upward trend along south facing shores today. This source will fade into the weekend with mainly background swell expected. For next week, chances for a solid south- southwest swell are rising based on the latest activity within our swell window southeast of New Zealand this morning. Expect a building trend through the day Tuesday with a peak centered around the Tuesday night through Thursday time frame next week.
Surf along east facing shores may briefly trend up over the weekend with the return of trades, but will ease early next week as the winds swing out of the southeast ahead of the front setting up to the west.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov