Hilo

Today: Mostly sunny with scattered showers. Highs around 82 near the shore to 66 to 72 at 4000 feet. Southeast winds around 10 mph. Chance of rain 40 percent.

Tonight: Partly cloudy with isolated showers. Lows around 65 near the shore to around 51 at 4000 feet. Light winds. Chance of rain 20 percent.

Monday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 81 near the shore to 66 to 71 at 4000 feet. Light winds becoming east around 10 mph in the afternoon. Chance of rain 50 percent.

Kona

Today: Mostly sunny with isolated showers. Highs around 83 near the shore to around 68 near 5000 feet. Light winds. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Lows 68 to 73 near the shore to around 55 near 5000 feet. Light winds. Chance of rain 20 percent.

Monday: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 83 near the shore to around 69 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 81 near the shore to 71 to 77 near 3000 feet. Light winds. Chance of rain 40 percent.

Tonight: Partly cloudy with isolated showers. Lows around 64 near the shore to 49 to 61 near 3000 feet. Light winds. Chance of rain 20 percent.

Monday: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 80 near the shore to 70 to 76 near 3000 feet. Light winds becoming east up to 10 mph in the afternoon. Chance of rain 50 percent.

Kohala

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 81 near the shore to 71 to 77 near 3000 feet. Light winds. Chance of rain 40 percent.

Tonight: Partly cloudy with isolated showers. Lows around 64 near the shore to 49 to 61 near 3000 feet. Light winds. Chance of rain 20 percent.

Monday: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 80 near the shore to 70 to 76 near 3000 feet. Light winds becoming east up to 10 mph in the afternoon. Chance of rain 50 percent.

South Big Island

Today: Mostly sunny with isolated showers. Highs around 83 near the shore to around 66 near 5000 feet. East winds around 10 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows around 70 near the shore to around 54 near 5000 feet. Northeast winds around 10 mph. Chance of rain 20 percent.

Monday: Sunny in the morning then becoming partly sunny. Isolated showers. Highs around 82 near the shore to around 68 near 5000 feet. East winds around 10 mph. Chance of rain 20 percent.

Puna

Today: Mostly sunny with scattered showers. Highs around 82 near the shore to 66 to 72 at 4000 feet. Southeast winds around 10 mph. Chance of rain 40 percent.

Tonight: Partly cloudy with isolated showers. Lows around 65 near the shore to around 51 at 4000 feet. Light winds. Chance of rain 20 percent.

Monday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 81 near the shore to 66 to 71 at 4000 feet. Light winds becoming east around 10 mph in the afternoon. Chance of rain 50 percent.

Waikoloa

Today: Mostly sunny with isolated showers. Highs around 84 near the shore to 64 to 71 above 4000 feet. Light winds. Chance of rain 20 percent.

Tonight: Mostly clear. Isolated showers in the evening. Lows 65 to 73 near the shore to 49 to 58 above 4000 feet. Light winds. Chance of rain 20 percent.

Monday: Mostly sunny. Isolated showers in the afternoon. Highs around 84 near the shore to 66 to 72 above 4000 feet. Light winds. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Trade winds will weaken on today through Monday as a cold front approaching the islands from the northwest weakens the surface ridge north of the state. Most areas will see brief passing showers favoring windward and mountain areas in the overnight to early morning hours. East slopes of the Big Island and Maui will see scattered showers through this morning. Expect afternoon sea breezes developing over each island through Monday. The cold front will stall near Kauai from Monday afternoon through Tuesday enhancing showers over the Garden Isle and Oahu to a lesser degree. The subtropical ridge will build north of the islands from Monday night onward with moderate to locally windy trade winds along with passing windward and mountain showers lasting through Friday.

Discussion

This mornings satellite picture continues to show a cold front roughly 500 miles northwest of Kauai drifting towards the state. A high pressure system northeast of the region continues to weaken ahead of this approaching front. Water vapor imagery shows a weak upper level low just southeast of the Big Island. Instability and upper level divergence around this upper low continues to move eastward away from Hawaii. Elsewhere, brief passing showers will diminish a few hours after sunrise this morning as trade winds diminish.
The subtropical ridge north of the islands continues to weaken as the cold frontal trough moves into the Central Pacific region. This weakening ridge will decrease large scale trade winds over the islands into a background east to southeast wind flow. Local scale land and sea breezes will develop over each island through Monday afternoon. Island surface heating and background sea breeze convergence will build clouds over island interior sections on Sunday and Monday afternoons. Limited shower activity will develop in the afternoon to early evening hours, as this surface forcing decreases, and the cumulus clouds start to collapse. Overnight land breezes will tend to clear out most of the cloud cover over the islands.
Monday night through Tuesday…A weakening cold front moves into Kauai enhancing clouds and shower activity over the Garden Isle. Oahu may be close enough to the frontal cloud band to see a slight enhancement in shower activity as the front diminishes. Trade winds will increase into the moderate to locally windy range as the high pressure ridge builds in behind the front. Strengthening trade winds will spread eastward to all islands by Tuesday morning. Clouds and passing showers will once again favor the windward and mountain areas as these stronger trade winds return. The front will diminish and the easterly trade winds will push the remnant cloud band westward away from Kauai from Tuesday night into Wednesday morning.
Wednesday through Friday…A pocket of cold air aloft will produce a weak upper level low over the region. Moderate to breezy trade winds and slight upper level instability from this cold pocket and upper low feature may enhance trade wind shower activity a bit through Friday. However precipitation amounts will remain fairly limited. The highest chances for showers are forecast along north and east slopes of each island mainly in the overnight to early morning time periods.

Aviation

Satellite data continues to show an area of low/mid lvl moisture maneuvering around and in the vicinity of the islands again this morning. Periods of bkn to ovc MVFR cigs continue to affect portions of the eastern and central islands, mainly windward Big Island and Maui. Mixing developing later this morning and during the afternoon will help diminish the MVFR cigs. Otherwise, weakening trade winds will continue from west to east across the state through today as a high pressure ridge to the north drifts northeast, while a frontal boundary approaches the islands from the northwest. Much lighter background winds today will allow for the development of diurnal circulations, with daytime sea breezes and nighttime land breezes. Overall expect mainly VFR conditions to continue at most locations, except for the MVFR cigs and vsby within showers that develop through this morning.
AIRMET Sierra continues for eastern portions of the state, especially windward Big Island to Maui, for tempo mountain obscuration as moist trade wind flow continues. AIRMET Tango continues for potential periods of tempo mod upper lvl turb across the portions of the state, as weak upper dynamics pass south of the region today.

Marine

As anticipated, no significant changes with the forecast this morning. Winds have lightened and are becoming more southeasterly as expected with the ridge to the north of the islands weakening as it moves to the southeast. The approaching front is about 600 miles northwest of Kauai but is expected to continue to move towards the islands over the next several days. As it does so, the ridge will be pushed closer to the islands, resulting in winds becoming light and variable late Sunday for Kauai and Oahu, before northeasterly winds arrive Monday afternoon with the front. Some thunderstorms have been observed along the front, and are possible in the offshore waters as early as Sunday night as the front enters the northwest waters. The offshore waters forecast includes mention of thunderstorms through the week with the front. Most of the unstable airmass with the front will be the northeast of the islands, but its possible thunderstorms could make it into the coastal waters. Will be monitoring the progression of the front to make any changes to the forecast.
The front is currently expected to stall around Kauai on Tuesday and gradually dissipate through Thursday as strong high pressure builds northwest of the state. Trade winds will ramp up to fresh to strong levels late Tuesday, especially along and just north of the front, and hold through at least Thursday. As the winds increase, Small Craft Advisories (SCA) could be needed for most waters.
The current northwest swell will continue to subside today. The next northwest swell will build Monday, peaking Tuesday when the direction will shift out of the north-northwest. North shore surf will likely top High Surf Advisory (HSA) levels Monday night and Tuesday, followed by a gradual decline Wednesday through Friday. Background south shore surf will be interrupted by a small south- southwest swell mid week. This swell will also bring SCA level seas to exposed waters starting near Kauai Monday night.
East shore surf will remain well below seasonal average into Monday. Wind swell will ramp up as the trade winds increase on Tuesday and Wednesday, but the islands will lie near the eastern edge of the fetch of strong trade winds, which will limit the growth of the local seas. Latest guidance continues to suggest east shore surf near HSA level as the trades build. Seas are projected to be slightly lower around Oahu and barely above seasonal average near the Big Island. This trade wind swell will persist through at least Thursday, and the combined seas from the trade wind swell and the above mentioned northwest to north- northwest swell will likely require a SCA Tuesday through Thursday for most waters.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov