Hilo

Today: Mostly sunny with isolated showers. Highs around 79 near the shore to around 68 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Tonight: Mostly clear with isolated showers. Lows around 62 near the shore to around 41 at 4000 feet. Light winds. Chance of rain 20 percent.

Thursday: Mostly sunny with isolated showers. Highs around 79 near the shore to 67 to 72 at 4000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Kona

Today: Mostly sunny until late afternoon then becoming partly sunny. Isolated showers. Highs around 82 near the shore to 64 to 71 near 5000 feet. Light winds. Chance of rain 20 percent.

Tonight: Mostly clear. Lows around 67 near the shore to around 44 near 5000 feet. Light winds.

Thursday: Sunny in the morning then becoming partly sunny. Isolated showers. Highs around 83 near the shore to 64 to 71 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

Today: Mostly sunny with isolated showers. Highs around 80 near the shore to around 71 near 3000 feet. Northeast winds around 10 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Lows around 63 near the shore to around 48 near 3000 feet. South winds around 10 mph.

Thursday: Mostly sunny with isolated showers. Highs around 79 near the shore to around 71 near 3000 feet. North winds up to 10 mph. Chance of rain 20 percent.

Kohala

Today: Mostly sunny with isolated showers. Highs around 80 near the shore to around 71 near 3000 feet. Northeast winds around 10 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Lows around 63 near the shore to around 48 near 3000 feet. South winds around 10 mph.

Thursday: Mostly sunny with isolated showers. Highs around 79 near the shore to around 71 near 3000 feet. North winds up to 10 mph. Chance of rain 20 percent.

South Big Island

Today: Mostly sunny with isolated showers. Highs around 81 near the shore to around 64 near 5000 feet. Southeast winds up to 10 mph in the morning becoming light. Chance of rain 20 percent.

Tonight: Mostly clear. Lows around 66 near the shore to around 43 near 5000 feet. North winds around 10 mph.

Thursday: Sunny in the morning then becoming partly sunny. Isolated showers. Highs around 81 near the shore to around 64 near 5000 feet. South winds up to 10 mph in the morning becoming light. Chance of rain 20 percent.

Puna

Today: Mostly sunny with isolated showers. Highs around 79 near the shore to around 68 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Tonight: Mostly clear with isolated showers. Lows around 62 near the shore to around 41 at 4000 feet. Light winds. Chance of rain 20 percent.

Thursday: Mostly sunny with isolated showers. Highs around 79 near the shore to 67 to 72 at 4000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Waikoloa

Today: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs around 81 near the shore to 65 to 73 above 4000 feet. Light winds. Chance of rain 20 percent.

Tonight: Mostly clear. Lows around 66 near the shore to 39 to 45 above 4000 feet. Light winds.

Thursday: Sunny in the morning then becoming partly sunny. Isolated showers. Highs around 80 near the shore to 65 to 73 above 4000 feet. Light winds. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Moderate trade winds will transition to more light and variable weather pattern today lasting through Friday, as a high pressure ridge weakens and drifts over the region. An approaching cold front will stall and diminish north of the island chain on Friday as high pressure builds in north of the state. Trade winds will return this weekend with increasing shower trends as bands of clouds from this remnant front drift over each island. An upper level low will set up just northeast of the islands creating more unstable trade wind showers into early next week.

Discussion

The big picture satellite imagery this morning shows a similar stable weather pattern for the Hawaiian Islands over the next few days, with a weakening surface ridge moving over the islands as a cold front approaches from the northwest. An upper level low lingers roughly 900 miles northeast of the Big Island. A few passing shower bands created by this upper low may drift into the windward sections of each island through the morning hours.
Trade winds will diminish this afternoon as the ridge axis weakens and moves over the islands chain. A more variable land and sea breeze pattern will develop over each island lasting through Friday night. Clouds will build over island mountain and interior sections due to converging sea breeze winds and island surface heating. Cooling of the land at night will cause down slope land breezes to form, clearing out cloud cover each evening. Expect limited rainfall in this pattern due to strong subsidence aloft from the high pressure ridge. A cold front approaching the islands will stall out and diminish north of the state on Friday. Remnant clouds with this dissipated frontal band will drift through the region on returning trade winds this weekend.
A high pressure system will drift eastward through the region on Saturday and Sunday, passing just north of the Hawaiian Islands. This system will increase large scale pressure gradients and allow a return to moderate trade wind weather with lingering sea breezes over terrain sheltered leeward slopes.
One wrinkle in the forecast from Saturday night onward is an upper level low moving into a position just northeast of the Hawaiian Islands. This unstable low will lift the trade wind temperature inversion, allowing clouds to build to higher heights, and produce more rainfall activity across the state. Both the American (GFS) and the European (ECMWF) models show this feature drifting into the region this weekend. There are still differences in the location, timing and strength of this low that will cause adjustments to our wet weather trends. However, at this point in time we have increased shower activity from Saturday night onward towards a wet trade wind pattern that appears to be more in line with our best guidance tools. Even leeward areas will see isolated to scattered showers developing. Subtle changes to the location and strength of this low will produce larger changes in our rainfall coverage for each island from this weekend into the first half of next week. Stay tuned for updates to the weather forecast as this pattern evolves over time.

Aviation

Background trade wind flow will continue to weaken in response to a slow moving cold front approaching from the northwest. Afternoon sea breezes and overnight land breezes will increasingly drive local weather. Expected clouds and showers to favor east facing slopes and coasts through this morning. Isolated shower activity will become focused over island interiors in the afternoon. Partial clearing expected along leeward coasts beginning after sunset.
The 2 AM satellite imagery reveals bands of low-topped cumulus off the Pacific approaching the islands from the east. An increasingly thick band of cloud cover can be seen enveloping the windward slopes of the Big Island and creeping towards the south end of Maui. Radar returns from the same time period indicate minimal precipitation associated with these clouds,
AIRMET Sierra has been issued for mountain obscuration for east facing slopes of the Big Island. Conditions are expected to improve after sunrise. For the smaller islands, brief MVFR CIG or VIS are to be expected in showers, but VFR conditions will prevail.

Marine

A ridge will move closer to the islands, maintaining gentle to moderate trade winds into the weekend. A low to the north northeast of the state may disrupt trade flow early next week.
A moderate west northwest swell will fill in through today and a High Surf Advisory remains in effect for exposed north and west- facing shores of the smaller islands through this afternoon. This swell will slowly subside Thursday through Friday. Very small, longer period background swell will keep south shore surf seasonably low for the next few days. Larger south swells could reach the state by early next week. Weak trades will keep east shore wave chop small through the weekend.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST this evening for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Molokai West, Windward Haleakala.

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Data Courtesy of NOAA.gov