West Side

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then isolated showers after midnight. Lows 66 to 72. East winds 10 to 20 mph. Chance of rain 50 percent.

Saturday: Partly sunny in the morning then becoming mostly sunny. Breezy. Isolated showers. Highs 76 to 82. East winds 10 to 25 mph. Chance of rain 20 percent.

Saturday Night: Breezy. Partly cloudy with scattered showers in the evening, then mostly cloudy with isolated showers after midnight. Lows 66 to 72. Northeast winds 10 to 25 mph decreasing to 10 to 15 mph after midnight. Chance of rain 50 percent.

South Side

Tonight: Partly cloudy. Lows 64 to 74. Northeast winds up to 15 mph.

Saturday: Mostly sunny. Breezy. Highs around 85. Northeast winds up to 20 mph.

Saturday Night: Partly cloudy. Breezy. Lows 64 to 74. Northeast winds 10 to 20 mph.

North Shore

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows around 69 near the shore to around 51 near 5000 feet. Southeast winds up to 20 mph. Chance of rain 70 percent.

Saturday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 76 to 81 near the shore to around 64 near 5000 feet. East winds 10 to 25 mph. Chance of rain 70 percent.

Saturday Night: Breezy. Mostly cloudy with numerous showers. Lows around 68 near the shore to around 51 near 5000 feet. East winds 10 to 25 mph decreasing to 10 to 15 mph after midnight. Chance of rain 70 percent.

Central Maui

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Isolated showers. Lows around 67. East winds 10 to 20 mph. Chance of rain 20 percent.

Saturday: Partly sunny in the morning then becoming mostly sunny. Breezy. Isolated showers. Highs 79 to 86. East winds 10 to 25 mph. Chance of rain 20 percent.

Saturday Night: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Isolated showers. Lows around 67. Northeast winds 10 to 25 mph decreasing to 10 to 15 mph after midnight. Chance of rain 20 percent.

Upcountry

Tonight: Breezy. Partly cloudy with scattered showers. Lows around 45 at the visitor center to around 43 at the summit. East winds up to 25 mph increasing to 10 to 25 mph after midnight. Chance of rain 50 percent.

Saturday: Breezy. Mostly sunny with scattered showers in the morning, then partly sunny with isolated showers in the afternoon. Highs around 60 at the visitor center to around 64 at the summit. East winds up to 25 mph. Chance of rain 50 percent.

Saturday Night: Breezy. Partly cloudy with scattered showers. Lows 43 to 53. East winds 10 to 25 mph. Chance of rain 50 percent.

East Maui

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows around 69 near the shore to around 51 near 5000 feet. Southeast winds up to 20 mph. Chance of rain 70 percent.

Saturday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 76 to 81 near the shore to around 64 near 5000 feet. East winds 10 to 25 mph. Chance of rain 70 percent.

Saturday Night: Breezy. Mostly cloudy with numerous showers. Lows around 68 near the shore to around 51 near 5000 feet. East winds 10 to 25 mph decreasing to 10 to 15 mph after midnight. Chance of rain 70 percent.

Lanai City

Tonight: Partly cloudy. Lows around 64. Northeast winds up to 15 mph.

Saturday: Breezy. Mostly sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Highs 72 to 80. Northeast winds up to 20 mph. Chance of rain 20 percent.

Saturday Night: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Lows 61 to 66. Northeast winds 10 to 20 mph.

Kaunakakai

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Isolated showers. Lows 56 to 72. East winds 10 to 20 mph. Chance of rain 20 percent.

Saturday: Breezy. Partly sunny with isolated showers. Highs 67 to 85. East winds 10 to 25 mph. Chance of rain 20 percent.

Saturday Night: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Isolated showers. Lows 56 to 72. East winds 15 to 20 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Breezy trade winds will continue for the next several days, with lighter winds expected by the middle of next week. Passing clouds and showers will favor windward slopes and coasts, with a few brief showers over leeward areas.

Discussion

Strong (~1035 mb) high pressure far NE of the islands is supporting locally strong trade winds this evening, with radar indicating reduced shower coverage as compared to recent days. Exposed/elevated wind gages on Maui and the Big Island reported gusts approaching 50 mph during the day today, but have diminished slightly since. Afternoon soundings show an elevated mixed layer and a weakened inversion, more notable over Kauai – likely due to a weak low aloft to the W. This low is sending broken to overcast high clouds over the islands, effectively obscuring low cloud coverage in traditional IR imagery. ProxyVis satellite data makes it easier to identify scattered to broken showery low cloud elements embedded in the upstream trade wind flow.
The forecast expects that trade winds will ease slightly in the short term, but remain locally breezy through the weekend and into next week as the high drifts eastward. While no organized moisture sources are expected to arrive on the trades, global and regional guidance indicates that periodic clusters of increased moisture will occasionally pass over the islands, bringing passing showers, primarily to windward slopes and coasts. The low aloft is expected to gradually move E and pass over the islands Sunday into early next week, supporting a somewhat unstable island atmosphere, and the notion that orographic lift will also trigger some shower formation (and rainbow development). Leeward areas may see some brief showers, but little accumulation is expected. High clouds will be diminishing on Saturday as they move N of the islands.
Latest round of guidance indicates winds are likely to weaken by the middle of next week as strong low pressure far N of the area forces the surface ridge near/over the islands. In this regime, island- scale land/sea breezes are likely to be the strongest modulator of island weather, with mostly clear nights and mornings giving way to afternoon clouds and showers over interior/leeward areas. Mid-level temperatures are expected to be cooler than normal due to a trough aloft, so briefly heavy downpours are not out of the question at this time.

Aviation

Breezy trades will continue for the next few days and carry batches of SHRA and low cigs across windward and mauka locations, with isol spillover into leeward areas. MVFR conds will be possible in heavier SHRA, otherwise VFR conds prevail.
AIRMET Sierra may be needed for mtn obsc for windward portions of the island chain late tonight into tomorrow morning with the increase in SHRA/low cigs.
AIRMET Tango is in effect for mod low level turb downwind of island terrain due to the breezy trades.

Marine

Fresh to strong trade winds will ease slightly tonight and Saturday as a robust 1035 mb surface high, now centered roughly 1125 nm northeast of Hawaii, moves east and slowly weakens. A Small Craft Advisory (SCA) will remain in effect for most waters overnight and will be scaled back to the typically windy waters around the Big Island and Maui County for Saturday and Sunday. A further drop in winds is expected on Tuesday as a developing front displaces the subtropical ridge southward toward the islands.
Rough, wind-driven seas will continue to slowly decline this weekend. Elevated rough surf along east facing shores of most islands will decline to near April average on Saturday and subside below average Sunday into early next week.
The combination of a declining north-northwest swell of around 2 feet at 11 to 12 seconds and wrapping wind swell will decline Saturday into Sunday. A small to moderate, medium period northwest swell due on Monday will push surf to near April average, followed by a decline Tuesday and Wednesday. A moderate, long period north-northwest swell may arrive Thursday.
Surf along south facing shores will be below April average this week. A small south swell of less than 2 feet at 15 seconds will decline on Saturday. Expect typical background level surf Sunday through much of the week.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Saturday for Kauai Northwest Waters, Kauai Leeward Waters, Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Big Island Windward Waters.
Small Craft Advisory until 6 PM HST Sunday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov