Photo Credit: James Grenz

Hilo

Today: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 82 near the shore to around 69 at 4000 feet. East winds up to 10 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 30 percent.

Tonight: Mostly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 62 to 67 near the shore to around 52 at 4000 feet. Southeast winds up to 10 mph shifting to the southwest after midnight. Chance of rain 30 percent.

Saturday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 81 near the shore to around 69 at 4000 feet. East winds up to 10 mph. Chance of rain 30 percent.

Kona

Today: Sunny in the morning then becoming mostly cloudy. Highs 80 to 85 near the shore to around 67 near 5000 feet. West winds up to 10 mph.

Tonight: Mostly cloudy with isolated showers in the evening, then mostly clear after midnight. Lows 69 to 74 near the shore to around 54 near 5000 feet. Light winds. Chance of rain 20 percent.

Saturday: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 80 to 86 near the shore to around 67 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

Today: Partly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 81 near the shore to 66 to 76 near 3000 feet. East winds 10 to 20 mph. Chance of rain 30 percent.

Tonight: Mostly cloudy. Breezy. Isolated showers in the evening, then scattered showers after midnight. Lows around 64 near the shore to 52 to 59 near 3000 feet. East winds 10 to 20 mph decreasing to up to 15 mph after midnight. Chance of rain 30 percent.

Saturday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 80 near the shore to 66 to 76 near 3000 feet. East winds up to 15 mph becoming around 10 mph in the afternoon. Chance of rain 30 percent.

Kohala

Today: Partly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 81 near the shore to 66 to 76 near 3000 feet. East winds 10 to 20 mph. Chance of rain 30 percent.

Tonight: Mostly cloudy. Breezy. Isolated showers in the evening, then scattered showers after midnight. Lows around 64 near the shore to 52 to 59 near 3000 feet. East winds 10 to 20 mph decreasing to up to 15 mph after midnight. Chance of rain 30 percent.

Saturday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 80 near the shore to 66 to 76 near 3000 feet. East winds up to 15 mph becoming around 10 mph in the afternoon. Chance of rain 30 percent.

South Big Island

Today: Mostly sunny in the morning then becoming mostly cloudy. Breezy. Highs around 83 near the shore to around 69 near 5000 feet. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon.

Tonight: Mostly cloudy in the evening then becoming mostly clear. Breezy. Lows around 70 near the shore to around 55 near 5000 feet. Northeast winds 10 to 25 mph.

Saturday: Mostly sunny. Breezy. Highs around 84 near the shore to around 69 near 5000 feet. East winds up to 20 mph becoming 10 to 15 mph in the afternoon.

Puna

Today: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 82 near the shore to around 69 at 4000 feet. East winds up to 10 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 30 percent.

Tonight: Mostly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 62 to 67 near the shore to around 52 at 4000 feet. Southeast winds up to 10 mph shifting to the southwest after midnight. Chance of rain 30 percent.

Saturday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 81 near the shore to around 69 at 4000 feet. East winds up to 10 mph. Chance of rain 30 percent.

Waikoloa

Today: Sunny in the morning then becoming partly sunny. Highs around 84 near the shore to 66 to 72 above 4000 feet. Northwest winds up to 15 mph becoming around 10 mph in the afternoon.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Lows 67 to 73 near the shore to 50 to 59 above 4000 feet. Northeast winds up to 10 mph in the evening becoming light.

Saturday: Mostly sunny. Highs around 85 near the shore to 66 to 73 above 4000 feet. Light winds.

Detailed Forecast

Synopsis

Moderate to locally breezy trade winds will persist into this afternoon, followed by weaker trade winds from tonight through this weekend. In addition, stable and dry atmospheric conditions will remain in place. High clouds will start to cover skies across much of the state as we head into the weekend, with minimal low clouds and trade showers along windward facing slopes. The trade winds are expected to be weak enough by Sunday to allow the development of afternoon sea breezes and nighttime land breezes. Expect the trade winds to gradually strengthen early next week.

Discussion

A nearly east to west oriented surface ridge is located less than 350 miles north of Honolulu. The relatively tight pressure gradient south of this feature is maintaining moderate to locally breezy trade winds across most of the state early this morning. The atmosphere remains dry and stable over the island chain. Scattered to broken low clouds, mainly stratocumulus, continue to be transported into the windward sides of the islands. Radar reflectivities show isolated light showers embedded within some of these stable low clouds, but rainfall totals are meager. Note that in addition to the low clouds, a large area of high clouds (mainly cirrus) is lurking just southeast of the Big Island. This is indicative of a subtropical jet stream that has been setting up south and southeast of the area.
The forecast guidance continues to show the surface ridge north of the area will weaken from later today and tonight into this weekend. This will cause the trade winds to gradually ease. At the same time, the large area of cirrus clouds near the Big Island will shift northward over portions of the island chain as the subtropical jet migrates closer to the islands. The dry and stable atmospheric conditions will also continue to limit the amount of low clouds and trade showers over windward facing slopes and coasts. The greatest coverage of windward showers will remain late at night and early in the morning.
By Sunday, the background trade wind flow is expected to be weak enough to allow alternating local afternoon sea breezes and nighttime land breezes. A weak mid-level trough located just west of Kauai may phase with a much broader trough aloft to the north. The subtropical jet will also likely remain near the eastern end of the state. These features aloft may weaken the low-level trade wind inversion slightly, but low- and mid-level moisture will remain limited. The sea breezes may therefore allow some clouds to develop over leeward and interior sections during the afternoon, but only spotty showers are expected. The nighttime land breezes will clear out most of the low clouds over these same areas after sunset.
The global forecast models indicate the trade winds will gradually strengthen from Memorial Day through early next week. At the same time, a mid-level ridge will reestablish its influence over the state, This will cause the atmosphere to become stable again. The dry weather pattern will mean limited low clouds, with only modest rainfall over windward and mauka sections next week.

Aviation

A high pressure ridge north of the islands will continue to keep moderate to locally breezy easterly trade winds blowing across the region today. A slight moderation of these trade wind speeds will occur this weekend with some afternoon sea breezes forming over terrain sheltered western slopes of each island. Otherwise, fairly stable and dry conditions will result in limited cloud and shower coverage.
A subtropical jet stream south of the region will drift northward over the islands with potential for producing moderate clear air turbulence over the islands from FL280 to FL350 later this morning. AIRMET Tango may be needed to cover this event. No AIRMETs are currently in effect.

Marine

Fresh to strong easterly trade winds will continue today, then trend down into the moderate to locally fresh category over the weekend as the ridge weakens and shifts southward into the area. The wind direction will respond and shift out of the east to southeast for a brief period Saturday night through Sunday, which will lead to localized land and sea breeze conditions near the coasts over the western end of the state. A return of fresh to strong easterly trade winds is expected early next week as the ridge retreats northward.
Surf along south facing shores will trend up into the weekend, then again next Tuesday through midweek as overlapping south swells associated with an active pattern near New Zealand move through. Surf heights could reach the advisory level of 10 ft (face value) later today through Saturday night, then to the warning level of 15 ft (face value) late Tuesday through Wednesday as the second swell moves in and peaks. Long-period forerunners (23 second periods) associated with the first south swell have already begun to show at our PacIOOS Barbers Point buoy overnight. Offshore buoy observations to the south reflect this rising trend with the peak energy centered in the 21 second band this morning. As a result, a High Surf Advisory has been issued for south facing shores from noon today through early Sunday.
Surf along exposed north and west facing shores will trend down today as a small, north-northwest swell moves out. A similar northwest swell (medium period) is expected by Sunday, which will linger into Monday before easing.
Surf along east facing shores will remain small and choppy each day with the trades in place. A brief downward trend is anticipated by Sunday as the winds ease and shift out of the east to southeast.

HFO Watches/Warnings/Advisories

High Surf Advisory from noon today to 6 AM HST Sunday for south facing shores of all Hawaiian Islands.
Small Craft Advisory until 6 PM HST this evening for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Big Island Now Weather is brought to you by Blue Hawaiian Helicopters.

Check out their Big Island Helicopter Tours today!

Data Courtesy of NOAA.gov