Photo Credit: James Grenz

Hilo

Today: Mostly cloudy. Numerous showers in the morning, then isolated showers in the afternoon. Highs around 85 near the shore to 70 to 75 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows around 68 near the shore to around 54 at 4000 feet. Northwest winds up to 15 mph. Chance of rain 70 percent.

Labor Day: Mostly cloudy with numerous showers. Highs around 85 near the shore to 70 to 75 at 4000 feet. North winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 70 percent.

Kona

Today: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 83 to 88 near the shore to around 70 near 5000 feet. Light winds. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Lows 69 to 75 near the shore to around 55 near 5000 feet. Light winds. Chance of rain 20 percent.

Labor Day: Sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 83 to 88 near the shore to around 70 near 5000 feet. Northwest winds up to 10 mph shifting to the southwest in the afternoon. Chance of rain 50 percent.

Waimea

Today: Mostly sunny in the morning then becoming partly sunny. Breezy. Isolated showers. Highs around 83 near the shore to 70 to 80 near 3000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows around 68 near the shore to 56 to 62 near 3000 feet. East winds 10 to 20 mph. Gusts up to 40 mph after midnight. Chance of rain 50 percent.

Labor Day: Mostly cloudy. Breezy. Scattered showers in the morning, then numerous showers in the afternoon. Highs around 83 near the shore to 70 to 80 near 3000 feet. East winds 10 to 20 mph. Gusts up to 40 mph in the morning. Chance of rain 60 percent.

Kohala

Today: Mostly sunny in the morning then becoming partly sunny. Breezy. Isolated showers. Highs around 83 near the shore to 70 to 80 near 3000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows around 68 near the shore to 56 to 62 near 3000 feet. East winds 10 to 20 mph. Gusts up to 40 mph after midnight. Chance of rain 50 percent.

Labor Day: Mostly cloudy. Breezy. Scattered showers in the morning, then numerous showers in the afternoon. Highs around 83 near the shore to 70 to 80 near 3000 feet. East winds 10 to 20 mph. Gusts up to 40 mph in the morning. Chance of rain 60 percent.

South Big Island

Today: Breezy. Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 87 near the shore to around 74 near 5000 feet. East winds up to 25 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Breezy. Lows around 70 near the shore to around 53 near 5000 feet. Northeast winds up to 20 mph.

Labor Day: Breezy. Sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs around 87 near the shore to around 74 near 5000 feet. East winds up to 20 mph. Chance of rain 40 percent.

Puna

Today: Mostly cloudy. Numerous showers in the morning, then isolated showers in the afternoon. Highs around 85 near the shore to 70 to 75 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows around 68 near the shore to around 54 at 4000 feet. Northwest winds up to 15 mph. Chance of rain 70 percent.

Labor Day: Mostly cloudy with numerous showers. Highs around 85 near the shore to 70 to 75 at 4000 feet. North winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 70 percent.

Waikoloa

Today: Breezy. Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 87 near the shore to 71 to 77 above 4000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Breezy. Lows 70 to 75 near the shore to 51 to 58 above 4000 feet. East winds up to 20 mph.

Labor Day: Breezy. Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 87 near the shore to 71 to 77 above 4000 feet. Northeast winds up to 20 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Trade winds will strengthen slightly today with moderate to locally breezy winds lasting through Monday. Trade winds will continue to blow at moderate levels through Thursday with lighter trade winds and afternoon sea breezes expected from Friday onward into next weekend. A series of weak disturbances moving through the region over the next seven days will bring periods of increasing cloud and shower trends to each island.

Discussion

The regional satellite picture this morning continues to show a high pressure ridge far north of the state. Cloud remnants from a low level trough (former cold front) just north of the islands will pass west of the state with little impact on island weather. Unstable clouds are drifting across the central islands in Maui County and Oahu this morning from a weak low level trough producing a brief increase in shower activity statewide, especially over windward and mountain areas. These showers will linger over the western islands of Kauai and Oahu through the morning hours before diminishing. Another larger low level trough approaching the Big Island from the east, currently near 143W longitude, will bring the next round of clouds and enhanced showers into the islands from Monday into Tuesday. In the upper levels, a narrow trough (the TUTT) continues to persist over the region.
The high pressure ridge north of the state will produce a slight increase in trade winds today with moderate to locally breezy conditions in the forecast. These moderate trades will continue through Thursday before decreasing from Friday through next weekend as the ridge weakens north of the state. Sea breezes will strengthen over the leeward slopes of each island during this time period of weaker trade winds.
On the weather side of the forecast, we see several weak low level troughs passing through the region this week bringing periods of increasing clouds and showers to each island. The first of these weak troughs is currently over the central islands this morning. This trough will weaken and pass into the western islands later this morning. Drying trends are expected today and tonight after the trough passes with more stable conditions in the short term forecast. By Monday morning however, another stronger easterly wave (700 mb trough) will move into the Big Island and Maui, deepening boundary layer moisture from east to west and increasing cloud and shower activity across the state into Tuesday morning. More typical trade wind weather will occur after this trough passes from the Tuesday afternoon through Thursday time period with trade wind inversion heights in the 5,000 to 7,000 foot range. Brief passing showers will favor windward and mountain areas, mainly in the overnight to early morning hours.
By Friday, trade wind speeds will become light and afternoon sea breezes will strengthen over leeward areas lasting through the upcoming weekend. Two weak low level troughs will pass through the region and deepen boundary layer moisture with trade wind inversion heights around 8,000 to 10,000 foot range. Expect enhanced afternoon to early evening mountain and interior section clouds and showers in this unstable sea breeze and light trade wind scenario.

Aviation

Moderate trade winds will continue to carry light showers off the Pacific toward the Islands. Showers will be most active in the late night and morning hours and impact mainly windward slopes and coasts. AIRMET Sierra is currently in effect for north and east facing slopes of Oahu, Molokai, and Maui. Conditions are expected to improve by mid-morning due to daytime heating.
Later today on the Big Island, light sea breezes along the leeward coast will drive afternoon and early evening cumulus development over the island's interior. The air mass over the state remains moderately unstable, so localized heavy showers are a possibility today.

Marine

Despite a series of systems in the North Pacific passing to its north, surface high pressure anchored north of the state will retain its characteristics through mid week. A subtle tightening of the pressure gradient over the islands the next couple of days will slightly strengthen easterlies. Today's fresh to locally strong trades has initiated a Small Craft Advisory for the typically windier waters around Maui County and Big Island through Labor Day afternoon. North Pacific systems look to become more progressive in their eastward journeys as high pressure to the west travels into the northeastern Pacific late this week and weakens the regional gradient and subsequent winds.
South-facing shore surf will remain low through the week with the continued passage of small, long period background south southwest swell. A swell originating from a gale moving east of New Zealand early this week will be directed within the island's south southwest swell window and is timed to reach our local waters next weekend. This slightly larger, medium to long period swell will support a noticeable increase in south shore surf. A series of small, medium period north swells from a couple of systems northwest of the state, between the western Aleutians and the International Date Line, will produce minor bumps to late week north-facing shore surf. East wind wave chop will remain slightly elevated under generally moderate to fresh east trade winds over and upstream of the islands.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Monday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov