Hilo

Today: Mostly sunny with isolated showers in the morning, then mostly cloudy with showers likely in the afternoon. Highs 77 to 83 near the shore to 65 to 71 at 4000 feet. Northeast winds around 10 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then showers likely after midnight. Lows 59 to 68 near the shore to 50 to 57 at 4000 feet. Light winds becoming northeast 10 to 15 mph after midnight. Chance of rain 60 percent.

Thursday: Mostly cloudy. Numerous showers in the morning, then numerous showers and chance of thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 76 to 82 near the shore to 63 to 69 at 4000 feet. North winds 10 to 15 mph decreasing to up to 15 mph in the afternoon. Chance of rain 70 percent.

Kona

Today: Sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 81 to 87 near the shore to around 66 near 5000 feet. Northwest winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 66 to 71 near the shore to 43 to 51 near 5000 feet. Northwest winds 10 to 15 mph. Chance of rain 30 percent.

Thursday: Mostly sunny with isolated showers in the morning, then mostly cloudy with scattered showers and chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 80 to 86 near the shore to around 65 near 5000 feet. Northwest winds 10 to 15 mph. Chance of rain 50 percent.

Waimea

Today: Mostly sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 62 to 84. North winds around 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 58 to 63 near the shore to 50 to 59 near 3000 feet. Light winds. Chance of rain 50 percent.

Thursday: Mostly cloudy. Numerous showers in the morning, then scattered showers and chance of thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 60 to 83. North winds 10 to 15 mph shifting to the northwest in the afternoon. Chance of rain 70 percent.

Kohala

Today: Mostly sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 62 to 84. North winds around 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 58 to 63 near the shore to 50 to 59 near 3000 feet. Light winds. Chance of rain 50 percent.

Thursday: Mostly cloudy. Numerous showers in the morning, then scattered showers and chance of thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 60 to 83. North winds 10 to 15 mph shifting to the northwest in the afternoon. Chance of rain 70 percent.

South Big Island

Today: Mostly sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs around 82 near the shore to around 66 near 5000 feet. Southwest winds around 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 68 near the shore to around 47 near 5000 feet. Southwest winds around 10 mph. Chance of rain 40 percent.

Thursday: Partly sunny. Breezy. Scattered showers in the morning, then numerous showers and chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 80 near the shore to around 64 near 5000 feet. Northwest winds 10 to 25 mph. Chance of rain 60 percent.

Puna

Today: Mostly sunny with isolated showers in the morning, then mostly cloudy with showers likely in the afternoon. Highs 77 to 83 near the shore to 65 to 71 at 4000 feet. Northeast winds around 10 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then showers likely after midnight. Lows 59 to 68 near the shore to 50 to 57 at 4000 feet. Light winds becoming northeast 10 to 15 mph after midnight. Chance of rain 60 percent.

Thursday: Mostly cloudy. Numerous showers in the morning, then numerous showers and chance of thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 76 to 82 near the shore to 63 to 69 at 4000 feet. North winds 10 to 15 mph decreasing to up to 15 mph in the afternoon. Chance of rain 70 percent.

Waikoloa

Today: Sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 80 to 86 near the shore to 64 to 69 above 4000 feet. North winds 10 to 15 mph shifting to the northwest in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy with isolated showers in the evening, then mostly clear after midnight. Lows 63 to 71 near the shore to 43 to 52 above 4000 feet. Light winds. Chance of rain 20 percent.

Thursday: Mostly sunny with isolated showers in the morning, then cloudy with numerous showers and chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 79 to 85 near the shore to around 65 above 4000 feet. Northwest winds around 10 mph. Chance of rain 60 percent.

Detailed Forecast

Synopsis

Light winds are expected to persist through the weekend, with northerly winds delivering a cool air mass the next couple of days. A passing disturbance aloft will bring the potential for a few heavy showers, and possibly a thunderstorm, tonight into Thursday. Stable and mostly dry conditions will prevail Friday through Sunday, as winds gradually become east and southeast. Chances for spotty heavy showers may increase Monday as a front moves over the islands.

Discussion

In summary, light winds will prevail through the weekend, potentially increasing early next week. While winds will be variable in direction today, they will become northerly tonight through Friday before veering to the NE on Saturday. An approaching front may turn winds to the SE and S as early as Sunday, with the front potentially moving through the island chain early next week. The strong ridge aloft extending over the area from the W is expected to retreat toward the SW over the next week or so, allowing a couple shortwave troughs to move over the islands from the NW. The first trough is expected tonight through Thursday night, before sliding E of the islands Friday and Saturday. Another short wave aloft is expected early next week, and may be accompanied by a surface front that moves over the islands on Monday.
In the short term, a somewhat stable land/sea breeze regime will remain in place. A weak surface trough N of the islands will keep winds light and variable today, with generally clear skies this morning, except for a few showers over windward Kauai. Afternoon sea breezes could lead to a few more showers than yesterday, as the approaching upper level trough begins to destabilize the atmosphere. A few heavy showers may flare over interior portions of the smaller islands, but the best chance for increased rainfall appears to be over SE Big Island and adjacent waters, due to increased moisture associated with another nearby trough. High-resolution model guidance continues to indicate heavy showers developing near and E of the Big Island this afternoon through Thursday morning, and the potential for a thunderstorm is forecast.
The island atmosphere will become unstable tonight and Thursday as the approaching mid- and upper-level trough drops 500 mb to near – 15C, but available moisture is expected to be limited. The trough aloft is expected to lead to surface cyclogenesis about 400 miles NE of the islands, leading to a light, weakly-convergent N wind flow that ushers in a somewhat cool air mass. Best chances for rainfall and thunderstorms will be on the Big Island, while the drier N flow is expected to support only isolated heavy showers and/or thunderstorms elsewhere. The summits of the Big Island will likely experience strong westerly winds and a wintry mix of precipitation, possibly requiring Wind/Winter Weather Advisories. There is also potential for frozen precip (most likely freezing rain) on the highest reaches of Haleakala if a heavy shower were to develop there.
Stable and mostly dry conditions will prevail for most areas Friday through Sunday as the trough aloft moves E of the area. Interior Big Island could see isolated heavy shower/thunderstorms Friday afternoon, but elsewhere rainfall should be limited. Light N winds will turn toward the E on Saturday, with only isolated showers expected. Winds may shift to the SE and S on Sunday as a deep-layer trough approaches from the NW, but showers will still be limited. The trough may send a front down the island chain on Monday, with spotty heavy showers possible.

Aviation

Light trades have focused low clouds and moderate to heavy showers over Windward Kauai early this morning. However, as the gradient continues to weaken, the land breeze has been increasingly able to push this activity into the adjacent waters. Meanwhile, moist southeast flow is pushing borderline MVFR ceilings southeast-facing slopes of the Big Island including Hilo. As the background flow turns light NNWly over the western end of the state, emerging sea breezes will tend to focus interior clouds and showers over southern and eastern sections of Kauai and Oahu this afternoon. For the Big Island, southwesterly flow in the mid-levels shifts the likely location for diurnal convection to the windward slopes where low stability may allow for a few locally heavy showers and attendant transient MVFR or IFR conditions.
AIRMET Sierra for mountain obscuration for Windward Kauai will most likely be allowed to expire on schedule at 1400z.

Marine

Light winds will shift northerly and increase to more widespread moderate speeds tonight as a surface trough develops to the northeast. The trough will be strong enough to send a moderate northeast swell across the islands Friday through Sunday, peaking early on Saturday.
An upper trough will dig southeastward near the state Thursday and bring a slight chance of thunderstorms for the windward coastal waters. Both surface and upper troughs will move out Friday with more stable trades building in. A front will approach from the northwest early next week.
The current moderate period northwest swell will continue to gradually subside through Thursday. A new northwest swell is expected to arrive Thursday night and could bring surf near advisory threshold for north facing shores on Friday, then decline this weekend. The current small long period south swell will hold today before tapering off on Thursday.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov