Hilo

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 58 to 66 near the shore to 46 to 54 at 4000 feet. Light winds becoming west up to 10 mph after midnight. Chance of rain 70 percent.

Friday: Cloudy with numerous showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 74 to 79 near the shore to 59 to 64 at 4000 feet. North winds up to 10 mph shifting to the northeast in the afternoon. Chance of rain 70 percent.

Friday Night: Mostly cloudy with isolated showers in the evening, then partly cloudy with scattered showers after midnight. Lows 58 to 65 near the shore to 46 to 52 at 4000 feet. East winds up to 10 mph shifting to the southwest after midnight. Chance of rain 30 percent.

Kona

Tonight: Mostly cloudy with isolated showers in the evening, then mostly clear after midnight. Lows around 68 near the shore to 42 to 48 near 5000 feet. Light winds. Chance of rain 20 percent.

Friday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 81 near the shore to around 64 near 5000 feet. West winds up to 10 mph. Chance of rain 40 percent.

Friday Night: Partly cloudy. Lows around 68 near the shore to 42 to 48 near 5000 feet. Light winds.

Waimea

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 58 to 67 near the shore to 50 to 58 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Mostly sunny in the morning then becoming partly sunny. Breezy. Isolated showers. Highs around 75 near the shore to 65 to 74 near 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Friday Night: Partly cloudy with isolated showers. Lows 58 to 67 near the shore to 50 to 57 near 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Kohala

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 58 to 67 near the shore to 50 to 58 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Mostly sunny in the morning then becoming partly sunny. Breezy. Isolated showers. Highs around 75 near the shore to 65 to 74 near 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Friday Night: Partly cloudy with isolated showers. Lows 58 to 67 near the shore to 50 to 57 near 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

South Big Island

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows around 69 near the shore to around 48 near 5000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Friday: Breezy. Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 80 near the shore to around 64 near 5000 feet. East winds up to 20 mph. Chance of rain 40 percent.

Friday Night: Partly cloudy. Isolated showers in the evening. Lows around 69 near the shore to around 48 near 5000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Puna

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 58 to 66 near the shore to 46 to 54 at 4000 feet. Light winds becoming west up to 10 mph after midnight. Chance of rain 70 percent.

Friday: Cloudy with numerous showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 74 to 79 near the shore to 59 to 64 at 4000 feet. North winds up to 10 mph shifting to the northeast in the afternoon. Chance of rain 70 percent.

Friday Night: Mostly cloudy with isolated showers in the evening, then partly cloudy with scattered showers after midnight. Lows 58 to 65 near the shore to 46 to 52 at 4000 feet. East winds up to 10 mph shifting to the southwest after midnight. Chance of rain 30 percent.

Waikoloa

Tonight: Mostly cloudy early in the evening then becoming partly cloudy. Scattered showers early in the evening, then isolated showers late in the evening. Lows around 68 near the shore to 45 to 51 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Friday: Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 79 to 84 near the shore to 62 to 68 above 4000 feet. East winds up to 15 mph shifting to the north in the afternoon. Chance of rain 20 percent.

Friday Night: Partly cloudy. Lows 65 to 71 near the shore to 45 to 50 above 4000 feet. Northeast winds up to 10 mph shifting to the east around 10 mph after midnight.

Detailed Forecast

Synopsis

Light to locally moderate trade winds will continue through this evening, with moderate trade winds returning tomorrow and persisting into next week. These lighter winds will focus showers over interior and leeward areas through the afternoon today and over windward areas at night. A slightly drier air mass will move in Friday afternoon, with generally fair weather conditions expected through early next week.

Discussion

Current radar and satellite imagery show isolated to scattered showers concentrated across windward coastal waters near Oahu and Maui County, with a few showers forming over leeward and interior areas across the island chain due to sea breeze development this afternoon.
Light to locally moderate trade winds will persist through this evening and likely remain light enough to maintain sea breeze shower activity into the early evening as a shortwave trough aloft induces a weakness in the surface ridge over the island chain. This shortwave trough combined with an area of modest low level moisture extending across the area is helping to enhance showers this afternoon as the shortwave trough dives southeast down the island chain and continues its trek eastward. Radar estimated rain rates in some of these showers are up to 1 to 2 inches per hour.
Moderate trade winds will return tomorrow as high pressure strengthens to the northeast and fills in across the state in the wake of the exiting shortwave trough. With the increasing stability from the surface ridge to the northeast and weak mid level ridging building in from the west, along with slightly drier air filtering in on the trades, shower activity should be minimal through the weekend. With the island chain remaining on the southwestern end of the surface high through the weekend and into next week, trades will generally be out of the east- southeast. Winds across the western end of the state will be weaker than the eastern end and have more of a southerly component, while winds across the eastern end of the state will be slightly stronger and more out of the east. The weaker winds across the western half may allow for isolated sea breeze activity with afternoon clouds and showers forming over a few leeward and interior areas, and the stronger winds across the eastern half will yield a more typical trade wind weather regime. As mid level ridging tries to remain in control through midweek next week, overall shower development will continue to be suppressed, but periodic pockets of moisture may bring brief upticks in shower activity.
At the very end of the forecast period, we might see a change in the pattern as model guidance shows a deep low forming well to the north of the state that may drag a front across the island chain Thursday night into Friday.

Aviation

Sea breezes have resulted in cloud build ups and a few showers over all islands this afternoon. AIRMET Sierra is posted for tempo mountain obscurations above 2500 feet on Kauai, Oahu, Molokai, Lanai, Maui and Big Island. These clouds and showers will dissipate over the island interiors and shift to windward slopes as trade winds begin to fill in later tonight.

Marine

A weak and nearly stationary surface ridge over waters just N of Kauai is supporting light to locally moderate winds that are favoring a NE-E direction. The ridge will move N and gradually strengthen starting Friday, moving as far N as 25N by Saturday, then remain E-W oriented along that latitude through the middle of next week. This will result in moderate to fresh E winds over Maui and Big Island waters, and light to moderate ESE winds over Kauai and Oahu waters.
Nearshore buoys in windward waters indicate seas of 7-9 feet, primarily in medium-period NE swell that has remained fairly robust through the day. While this swell will gradually decline Friday through Saturday, it warrants an extension of the High Surf Advisory (HSA) for E facing shores through Friday, where HSA criteria is 10 feet.
Long-period (19-21 seconds) forerunners of a new NW swell have been slowly increasing in height at NDBC buoys 51001/51101 NW of Kauai today. Recent altimeter passes indicate that this swell will likely be larger than model estimates when it arrives, and overnight buoy observations will be used to fine-tune Friday's surf forecast. Regardless, high surf is expected along exposed N and W facing shores as the swell builds tonight and peaks on Friday, with peak surf heights as high as 20 feet. A HSA is in effect for N and W facing shores through Saturday morning. A similarly-sized (or slightly smaller) NW swell is expected from Saturday night into Monday, which may lead to an extension of the HSA. A potentially larger WNW swell is looking increasingly likely from late Tuesday into Thursday next week. A small S swell is possible around the middle of next week.
A Small Craft Advisory (SCA) for combined seas of 10 feet or greater has been issued for zones exposed to the increasing NW swell and lingering NE swell. Seas may again reach criteria over the weekend, and E winds may also reach SCA speeds in zones around Maui and the Big Island this weekend.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Saturday for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Molokai West, Windward Haleakala.
High Surf Advisory until 6 PM HST Friday for Olomana, Kauai East, East Honolulu, Koolau Windward, Molokai Southeast, Kipahulu, Big Island East, Big Island North.
Small Craft Advisory until 6 AM HST Saturday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters.

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Data Courtesy of NOAA.gov