Hilo

Tonight: Mostly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 61 to 68 near the shore to 51 to 56 at 4000 feet. Southwest winds up to 10 mph in the evening becoming light. Chance of rain 30 percent.

Thursday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 77 to 83 near the shore to 64 to 70 at 4000 feet. South winds up to 10 mph shifting to the east in the afternoon. Chance of rain 30 percent.

Thursday Night: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 60 to 67 near the shore to 49 to 55 at 4000 feet. Light winds. Chance of rain 60 percent.

Kona

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows around 71 near the shore to 45 to 51 near 5000 feet. Light winds. Chance of rain 20 percent.

Thursday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 84 near the shore to around 68 near 5000 feet. Northwest winds up to 10 mph. Chance of rain 30 percent.

Thursday Night: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows around 70 near the shore to 44 to 51 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

Tonight: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows 61 to 70 near the shore to 53 to 60 near 3000 feet. Light winds. Chance of rain 20 percent.

Thursday: Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 63 to 81. Light winds. Chance of rain 20 percent.

Thursday Night: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 60 to 69 near the shore to 52 to 59 near 3000 feet. East winds up to 10 mph increasing to 10 to 15 mph after midnight. Chance of rain 50 percent.

Kohala

Tonight: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows 61 to 70 near the shore to 53 to 60 near 3000 feet. Light winds. Chance of rain 20 percent.

Thursday: Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 63 to 81. Light winds. Chance of rain 20 percent.

Thursday Night: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 60 to 69 near the shore to 52 to 59 near 3000 feet. East winds up to 10 mph increasing to 10 to 15 mph after midnight. Chance of rain 50 percent.

South Big Island

Tonight: Mostly cloudy with isolated showers. Lows around 71 near the shore to around 50 near 5000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Thursday: Partly sunny with isolated showers. Highs around 83 near the shore to around 67 near 5000 feet. East winds up to 15 mph shifting to the southeast in the afternoon. Chance of rain 20 percent.

Thursday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy after midnight. Lows around 71 near the shore to around 49 near 5000 feet. Northeast winds around 10 mph. Chance of rain 30 percent.

Puna

Tonight: Mostly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 61 to 68 near the shore to 51 to 56 at 4000 feet. Southwest winds up to 10 mph in the evening becoming light. Chance of rain 30 percent.

Thursday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 77 to 83 near the shore to 64 to 70 at 4000 feet. South winds up to 10 mph shifting to the east in the afternoon. Chance of rain 30 percent.

Thursday Night: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 60 to 67 near the shore to 49 to 55 at 4000 feet. Light winds. Chance of rain 60 percent.

Waikoloa

Tonight: Partly cloudy. Isolated showers in the evening. Lows around 71 near the shore to 49 to 54 above 4000 feet. Light winds. Chance of rain 20 percent.

Thursday: Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 81 to 86 near the shore to 64 to 71 above 4000 feet. Light winds. Chance of rain 20 percent.

Thursday Night: Partly cloudy. Isolated showers after midnight. Lows 68 to 73 near the shore to 47 to 52 above 4000 feet. Light winds. Chance of rain 20 percent.

Detailed Forecast

Synopsis

The combination of southerly winds, moisture ahead of an approaching front, and upper troughing will increase rainfall chances for portions of the state tonight through the second half of the week. The front will reach Kauai tomorrow, then stall and begin to diminish near Oahu tomorrow night into Friday. Breezy north-northeast winds will fill in behind it tomorrow and tomorrow night. Trades will return briefly on Friday. A second front passing north of the area over the weekend could cause trades to weaken again.

Discussion

The subtropical ridge has been pushed south across the islands, resulting in southerly flow across the western portion of the chain and southeasterlies farther to the east. A ragged 400 mile wide band of broken to overcast layered clouds northwest of Kauai marks an approaching front. As this front continues its approach, rainfall will increase tonight, especially across the western islands, as upper troughing digs southward into the area. The combination of southerly winds and lift ahead of the approaching front could trigger pre-frontal showers. Radar and satellite loops show this potential, with increased cloud cover and developing showers noted over and around Oahu and Kauai. Instability will increase tonight over and around Kauai as the front draws closer. Thunderstorms can't be completely ruled out tonight into Thursday, especially around Kauai.
Models show the front will stall and slowly diminish around Oahu Thursday night through Friday as the upper trough lifts northeastward and away from the area. Breezy north to north- northeast winds behind the front tomorrow and tomorrow night over the western end of the state will veer out of the east on Friday. This will push residual frontal moisture westward. A brief return of light trade winds is possible over the weekend as another front passes to the north.

Aviation

A few showers embedded within light southerly flow will approach southwestern Kauai during the next few hours and may graze portions of western Oahu as well. These showers may bring a brief deterioration to MVFR on an isolated basis. Otherwise, high stability and VFR prevail into tonight as southerlies in advance of an approaching front strengthen sufficiently to offset land breeze potential in most locations. A solid band of moisture along the front will bring MVFR clouds and showers to Kauai, particularly the west and south-facing slopes, late tonight into Thursday morning. Kauai and Oahu see a transition to NNE trades in the wake of the front on Thursday afternoon.
No AIRMETs in effect. AIRMET Sierra will likely be needed for portions of Kauai late tonight into early Thursday morning.

Marine

A near east-to-west surface ridge axis laying across the waters is supporting statewide light to gentle variable breezes. The ridge orientation will generally provide south southwest winds over the Kauai and Oahu coastal waters, variable or south around breezes Maui and south southeasterlies around Big Island. The eastern passage of an upper trough to the north will displace ridging to the east on Friday. It will also push a surface cold front into the local western waters. This front is timed to reach Kauai's nearshore waters tomorrow (Thursday) morning and stall out somewhere over the central waters Friday into Saturday. Thus, expect brief period strong north northeast post-frontal winds to impact Kauai's surrounding waters Thursday afternoon with northerlies significantly dropping off as the front passes in the vicinity of Oahu Thursday evening. The approaching front will introduce a slight chance of thunderstorms for those waters surrounding Niihau, Kauai and the Kauai Channel from the early Thursday morning hours through the afternoon tomorrow. Winds and/or seas will likely reach Small Craft Advisory (SCA) criteria Thursday and Friday, focused over the western half of the state, from the frontal passage in tandem with a passing northwest swell. The front will weaken as it becomes more zonal in direction Friday afternoon. Gentle to moderate trade flow will establish itself going into Saturday. Trades will strengthen to fresh to locally strong magnitudes by next Tuesday into Wednesday as surface high pressure builds in northeast of the island chain.
The ongoing short period, near 7 foot swell will hold through the next north northwest swell arrival tomorrow. Long fetches produced within very large areas of near-gale to gale-force winds in association with low pressure systems passing far north of the area will send north to northwest swell of varying sizes and periods toward the islands the next several days. Most of this swell energy will be confined to the relatively shorter period bands. Resultant surf is expected to be near or above HSA heights along exposed north and west-facing shores going into the weekend.
A long period, very small south swell will gradually decline through tomorrow (Thursday). Another similar south swell is expected from Friday afternoon through the weekend, but it will may come in a touch smaller than this most recent swell.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov