Photo Credit: James Grenz

Hilo

Today: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 86 near the shore to 69 to 75 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 69 near the shore to around 55 at 4000 feet. North winds up to 15 mph. Chance of rain 50 percent.

Thursday: Mostly sunny with scattered showers. Highs around 86 near the shore to 70 to 76 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Kona

Today: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 82 to 87 near the shore to around 69 near 5000 feet. Light winds. Chance of rain 40 percent.

Tonight: Partly cloudy with isolated showers. Lows 70 to 75 near the shore to around 56 near 5000 feet. Light winds. Chance of rain 20 percent.

Thursday: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 83 to 88 near the shore to around 70 near 5000 feet. Light winds. Chance of rain 50 percent.

Waimea

Today: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 84 near the shore to 69 to 80 near 3000 feet. East winds 10 to 20 mph decreasing to up to 20 mph in the afternoon. Chance of rain 40 percent.

Tonight: Partly cloudy with isolated showers. Lows around 69 near the shore to 57 to 63 near 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Thursday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 84 near the shore to 70 to 80 near 3000 feet. East winds up to 15 mph. Chance of rain 40 percent.

Kohala

Today: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 84 near the shore to 69 to 80 near 3000 feet. East winds 10 to 20 mph decreasing to up to 20 mph in the afternoon. Chance of rain 40 percent.

Tonight: Partly cloudy with isolated showers. Lows around 69 near the shore to 57 to 63 near 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Thursday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 84 near the shore to 70 to 80 near 3000 feet. East winds up to 15 mph. Chance of rain 40 percent.

South Big Island

Today: Breezy. Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 86 near the shore to around 73 near 5000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Isolated showers in the evening. Lows around 71 near the shore to around 54 near 5000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Thursday: Mostly sunny. Scattered showers in the afternoon. Highs around 87 near the shore to around 74 near 5000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Puna

Today: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 86 near the shore to 69 to 75 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 69 near the shore to around 55 at 4000 feet. North winds up to 15 mph. Chance of rain 50 percent.

Thursday: Mostly sunny with scattered showers. Highs around 86 near the shore to 70 to 76 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Waikoloa

Today: Mostly sunny. Isolated showers in the afternoon. Highs around 86 near the shore to 70 to 76 above 4000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Isolated showers in the evening. Lows around 73 near the shore to 52 to 59 above 4000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Thursday: Mostly sunny. Scattered showers in the afternoon. Highs around 87 near the shore to 71 to 77 above 4000 feet. North winds up to 10 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Locally breezy trade winds will persist across the state today with passing clouds and showers favoring windward and mountain areas, primarily during the early morning hours. The trades will ease tonight, with light to moderate trades then expected Thursday through the weekend. This lighter wind regime will have showers favoring windward slopes and coasts at night and during the early morning hours, with showers developing over island interior and leeward areas each afternoon, then fizzling out during the evening. A more typical trade wind shower pattern appears to return early next week as the trades strengthen back to moderate levels.

Discussion

Currently at the surface, a 1031 mb high is centered around 1800 miles north-northeast of Honolulu, and is driving moderate to breezy trade winds across the island chain early this morning. Infrared satellite imagery shows partly to mostly cloudy conditions in windward areas, with clear to partly cloudy skies in most leeward locales. Radar imagery shows scattered showers moving into windward areas, with a few decaying showers or sprinkles reaching leeward communities at times. Main short term focus revolves around trade wind trends and rain chances during the next several days.
High pressure north-northeast of the state will keep moderate to breezy trade winds in place today. The trades will ease tonight and hold at light to moderate levels Thursday through the weekend as a series of weak troughs pass by to the north of the state. The trades during this time will be light enough to support localized land and sea breezes in the more sheltered leeward areas. Ridging looks to re-strengthen north of the islands early next week, with trades responding and strengthening to moderate levels.
As for the remaining weather details, we should see scattered showers continue into the early morning hours, before drier more stable conditions settle in by late morning and continue into this evening, with sparse shower activity confined primarily to windward slopes. We should see another nocturnal increase in trade wind showers tonight, with showers continuing to favor windward areas. The pattern appears to change slightly beginning Thursday and continuing through the weekend, as the trade winds ease. Bands of enhanced moisture will swing through the islands fairly regularly during this time. Showers will favor windward slopes and coasts, particularly at night and during the early morning hours, with showers also developing over the island interiors and leeward areas each afternoon and fizzling out in the evening. A more typical mainly windward focused shower pattern appears to return early next week.

Aviation

Breezy trades will focus occasional clouds and limited showers to windward and mauka zones through the first half of tonight before weakening slightly. Periodic MVFR will be possible, especially within any heavier showers, but VFR is forecast to prevail.
No AIRMETs are in effect.

Marine

A high pressure system far north of the state will drive moderate to locally strong trade winds through this afternoon, and a Small Craft Advisory (SCA) remains in effect for the typically windier waters around Maui County and Big Island. Winds will begin to weaken starting tonight as the high lifts northward, and wind speeds will trend lower through Friday. Trade winds will fall into gentle to moderate range by Thursday with wind speeds likely remaining below SCA thresholds through the first half of next week.
South shore surf will remain around seasonal average heights today and will slowly trend lower through Thursday. A pulse of small southwest swell may build by Friday. A larger south- southwest swell will build into the region from Saturday night to Sunday and peak on Monday. This larger south swell will produce surf heights above seasonal average levels through Tuesday.
North shore surf will remain below the September average through the week, with only small pulses of swell. Stronger trade winds upwind of the state will produce east shore surf near seasonal average levels today, followed by a decline from Thursday to Friday. East Pacific Hurricane Kay could send a small long period swell to east facing shores this weekend.

HFO Watches/Warnings/Advisories

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