Photo Credit: James Grenz

Hilo

Today: Mostly cloudy. Occasional showers in the morning, then showers likely in the afternoon. Highs 72 to 78 near the shore to 58 to 65 at 4000 feet. North winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 80 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then showers likely after midnight. Lows 57 to 69 near the shore to around 50 at 4000 feet. Northwest winds up to 15 mph. Chance of rain 70 percent.

Sunday: Partly sunny with showers likely. Highs 74 to 79 near the shore to 60 to 65 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 70 percent.

Kona

Today: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 80 near the shore to around 62 near 5000 feet. Southwest winds up to 10 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Scattered showers in the evening. Lows 63 to 68 near the shore to 43 to 50 near 5000 feet. Light winds. Chance of rain 40 percent.

Sunday: Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 80 near the shore to around 63 near 5000 feet. West winds up to 10 mph. Chance of rain 50 percent.

Waimea

Today: Breezy. Partly sunny with scattered showers. Highs 58 to 78. East winds 10 to 25 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 56 to 62 near the shore to 49 to 58 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Sunday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 60 to 79. East winds up to 15 mph. Chance of rain 50 percent.

Kohala

Today: Breezy. Partly sunny with scattered showers. Highs 58 to 78. East winds 10 to 25 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 56 to 62 near the shore to 49 to 58 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Sunday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 60 to 79. East winds up to 15 mph. Chance of rain 50 percent.

South Big Island

Today: Mostly sunny. Isolated showers in the afternoon. Highs around 78 near the shore to around 62 near 5000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 20 percent.

Tonight: Mostly clear. Lows around 68 near the shore to around 48 near 5000 feet. Northeast winds up to 10 mph.

Sunday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs around 79 near the shore to around 62 near 5000 feet. East winds up to 15 mph shifting to the southeast in the afternoon. Chance of rain 20 percent.

Puna

Today: Mostly cloudy. Occasional showers in the morning, then showers likely in the afternoon. Highs 72 to 78 near the shore to 58 to 65 at 4000 feet. North winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 80 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then showers likely after midnight. Lows 57 to 69 near the shore to around 50 at 4000 feet. Northwest winds up to 15 mph. Chance of rain 70 percent.

Sunday: Partly sunny with showers likely. Highs 74 to 79 near the shore to 60 to 65 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 70 percent.

Waikoloa

Today: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs 77 to 83 near the shore to around 63 above 4000 feet. Northeast winds up to 25 mph increasing to 10 to 25 mph in the afternoon. Chance of rain 20 percent.

Tonight: Mostly clear. Breezy. Lows 63 to 68 near the shore to 42 to 50 above 4000 feet. Southeast winds up to 20 mph.

Sunday: Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 77 to 82 near the shore to 61 to 66 above 4000 feet. Northwest winds up to 10 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Locally breezy trade winds will focus clouds and passing showers over windward areas this weekend, with high clouds thickening on Sunday. A deep low will develop several hundred miles northwest of Kauai late Sunday then dive south and weaken Monday and Tuesday. During this time, local winds will shift out of the east to southeast, and an increase showers will be possible, especially over the western end of the state. While high clouds will linger overhead, drier easterly trade winds are expected by mid week. Unsettled weather could return over some areas late next week.

Discussion

Locally breezy trade winds are pushing a band of low level moisture across the islands this morning. Showers have been focused across windward areas, where mainly less than half an inch of rain has fallen overnight, but a few standout sites on Kauai, Oahu, and Maui have recorded over an inch. This band is poised to clear Kauai and will pass Oahu around sunrise.
A persistent blocking pattern will remain in control across the Pacific this week. This pattern is producing the strong and deep high far north of the state that is generating the breezy trade winds. Energy from a strong west Pacific jet stream is undercutting this high in the upper levels and is connecting with an upper level trough that extends over the islands and off to the east. At this time, mid level ridging is strong enough to keep the weather over the state relatively stable, and the afternoon soundings continued to show hints of a weak low level inversion.
Only subtle changes are expected today. The west Pacific jet stream will carve out a trough about 800 miles west of Kauai and push a strong cold front eastward. This will help to slightly weaken the high to our north, leading to a brief decrease in the trade winds. The band of moisture will clear windward Maui County later this morning and the Big Island this afternoon, though leeward Big island could experience a few more afternoon showers compared to yesterday. Shower activity will be minimal on Kauai and Oahu through much of the day then pick up across windward slopes in the evening as another band of shallow moisture approaches.
A deep cutoff low will develop 700 to 800 miles northwest of the state on Sunday then weaken and drift southward Monday and Tuesday. Winds will shift out of the east to southeast and increase late Sunday and Monday as a band of deep moisture develops 250 to 400 miles west of Kauai. The upper level trough supporting the low will send thickening high clouds eastward and will erode the mid level currently overhead. This could enhance shower activity locally, especially for the western end of the island chain, though the greatest instability will remain west and south of Kauai. Expect rainfall to remain focused over windward slopes.
Moderate easterly trade winds will prevail late Tuesday and Wednesday, and instability may wane as the deep low gradually weakens several hundred miles southwest of the state. That said, high clouds will linger, and slightly drier air moving in on the trade wind flow could lead to diminishing rainfall.
Uncertainty grows heading into late next week. The west Pacific jet stream will send energy southward and reinvigorate the low west of the islands. The GFS and ECMWF are hinting at a broad convergent band redeveloping near or possibly over the state, bringing back a threat of unsettled weather.

Aviation

A strong high pressure system remains locked in place far north of the Hawaiian Islands through the weekend. Subtle changes in the strength of the ridge over the islands will weaken the trade winds speeds a bit through Sunday. An upper level disturbance will keep periods of showers in the forecast across the region with MVFR conditions mainly over north through east sections of all islands. Shower activity will favor the overnight to early morning hours.
AIRMET Sierra was issued during the evening for mountain obscurations over the north through east sections of Kauai, Oahu, Molokai, Maui and the Big Island. These MVFR conditions will decrease in coverage after sunrise this morning.
AIRMET Tango remains in place for low level moderate turbulence over mountains and south through west of mountain ranges. A downward trend in the winds is expected this morning, with wind speeds dropping below moderate turbulence thresholds for these areas.

Marine

Trade winds will continue across the Hawaiian Islands through Thursday of next week as a broad 1038 mb surface high remains nearly stationary far north of the islands. The high has weakened slightly overnight, and will continue into tonight. So the trades will be trending from moderate to locally strong to moderate speed tonight. Fresh trades will then hold through Sunday before trending up to fresh to locally strong Sunday night. This range will hold through Wednesday before falling off to moderate speed Wednesday night and Thursday.
The north-northeast swell has trended down in the evening, and now will hold at moderate level through Sunday. With the east swell having subsided as well, the surf along east facing shores has lowered to be high surf advisory criteria. Therefore the High Surf Advisory is canceled.
The north-northeast swell will shift to the northeast tonight and hold through at least Tuesday. There is a potential boost with the northeast swell Sunday night, perhaps related to the uptick in the in the trade winds combined with developing gale area a few hundred miles east of the islands. Surf may get up to near high surf advisory Monday before tending lower gradually thereafter.
West facing shores can expect small to moderate surf starting Monday and persist through most of next week as a series of long period west-northwest pulses move through the region.

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.

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Data Courtesy of NOAA.gov