Photo Credit: Randy Alona Gallegos

West Side

Today: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 71 to 80. East winds up to 20 mph shifting to the northeast in the afternoon. Chance of rain 50 percent.

Tonight: Partly cloudy. Breezy. Scattered showers in the evening, then isolated showers after midnight. Lows 62 to 68. East winds up to 20 mph. Chance of rain 30 percent.

Sunday: Breezy. Partly sunny with isolated showers. Highs 72 to 81. Northeast winds up to 20 mph. Chance of rain 20 percent.

South Side

Today: Sunny. Isolated showers in the morning. Highs around 82. North winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 20 percent.

Tonight: Mostly clear. Lows 61 to 68. Northeast winds up to 15 mph. Gusts up to 35 mph.

Sunday: Partly sunny. Highs around 83. North winds up to 15 mph shifting to the northeast in the afternoon.

North Shore

Today: Breezy. Mostly cloudy with occasional showers in the morning, then mostly sunny with scattered showers in the afternoon. Highs 71 to 77 near the shore to around 60 near 5000 feet. Southeast winds up to 20 mph shifting to the east 10 to 20 mph in the afternoon. Chance of rain 80 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then showers likely after midnight. Lows around 66 near the shore to 44 to 50 near 5000 feet. Southeast winds up to 15 mph. Chance of rain 70 percent.

Sunday: Breezy. Partly sunny with scattered showers. Highs 73 to 79 near the shore to around 62 near 5000 feet. Southeast winds up to 20 mph shifting to the east 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Central Maui

Today: Breezy. Partly sunny with scattered showers in the morning, then sunny in the afternoon. Highs 76 to 81. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Mostly clear. Isolated showers after midnight. Lows 61 to 69. East winds 10 to 15 mph. Chance of rain 20 percent.

Sunday: Breezy. Partly sunny with isolated showers. Highs 77 to 83. East winds 10 to 20 mph. Chance of rain 20 percent.

Upcountry

Today: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs around 57 at the visitor center to around 52 at the summit. Northeast winds up to 15 mph shifting to the east in the afternoon. Chance of rain 50 percent.

Tonight: Breezy. Partly cloudy with scattered showers. Lows around 43 at the visitor center to around 40 at the summit. East winds up to 20 mph increasing to 10 to 20 mph after midnight. Chance of rain 50 percent.

Sunday: Partly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 57 at the visitor center to around 52 at the summit. East winds up to 25 mph. Chance of rain 50 percent.

East Maui

Today: Breezy. Mostly cloudy with occasional showers in the morning, then mostly sunny with scattered showers in the afternoon. Highs 71 to 77 near the shore to around 60 near 5000 feet. Southeast winds up to 20 mph shifting to the east 10 to 20 mph in the afternoon. Chance of rain 80 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then showers likely after midnight. Lows around 66 near the shore to 44 to 50 near 5000 feet. Southeast winds up to 15 mph. Chance of rain 70 percent.

Sunday: Breezy. Partly sunny with scattered showers. Highs 73 to 79 near the shore to around 62 near 5000 feet. Southeast winds up to 20 mph shifting to the east 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Lanai City

Today: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 69 to 77. Northeast winds 10 to 20 mph. Chance of rain 30 percent.

Tonight: Mostly clear. Lows 57 to 62. Northeast winds up to 15 mph.

Sunday: Partly sunny. Isolated showers in the afternoon. Highs 68 to 77. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Kaunakakai

Today: Mostly sunny with isolated showers. Highs 62 to 82. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Lows 53 to 68. East winds up to 15 mph increasing to 10 to 15 mph after midnight.

Sunday: Partly sunny. Isolated showers in the afternoon. Highs 63 to 82. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 20 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