Photo Credit: Tyler Rooke

West Side

Today: Sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 79 to 89. Light winds becoming northwest up to 10 mph in the afternoon. Chance of rain 40 percent.

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy after midnight. Lows 69 to 76. East winds up to 10 mph. Chance of rain 20 percent.

Wednesday: Partly sunny. Isolated showers in the afternoon. Highs 80 to 91. East winds 10 to 15 mph. Chance of rain 20 percent.

South Side

Today: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs around 88. North winds up to 10 mph shifting to the west in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy after midnight. Lows 68 to 75. North winds up to 15 mph. Chance of rain 20 percent.

Wednesday: Partly sunny. Isolated showers in the afternoon. Highs around 90. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

North Shore

Today: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 77 to 85 near the shore to around 66 near 5000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 72 near the shore to 49 to 55 near 5000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Wednesday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 78 to 86 near the shore to around 68 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Central Maui

Today: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 81 to 88. North winds up to 10 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy. Isolated showers in the evening. Lows 68 to 73. East winds up to 10 mph. Chance of rain 20 percent.

Wednesday: Partly sunny with isolated showers. Highs 83 to 90. East winds 10 to 15 mph. Chance of rain 20 percent.

Upcountry

Today: Mostly sunny in the morning then becoming mostly cloudy. Scattered showers. Highs around 62 at the visitor center to around 57 at the summit. Light winds. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 45 at the visitor center to around 43 at the summit. Light winds becoming southeast up to 10 mph after midnight. Chance of rain 40 percent.

Wednesday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 64 at the visitor center to around 59 at the summit. East winds 10 to 15 mph. Chance of rain 50 percent.

East Maui

Today: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 77 to 85 near the shore to around 66 near 5000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 72 near the shore to 49 to 55 near 5000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Wednesday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 78 to 86 near the shore to around 68 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Lanai City

Today: Sunny with isolated showers in the morning, then mostly cloudy with scattered showers in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 72 to 81. Light winds. Chance of rain 40 percent.

Tonight: Mostly cloudy. Scattered showers in the evening. Lows around 66. Light winds. Chance of rain 30 percent.

Wednesday: Mostly cloudy. Scattered showers in the afternoon. Highs 74 to 82. Light winds becoming northeast around 10 mph in the afternoon. Chance of rain 30 percent.

Kaunakakai

Today: Sunny in the morning then becoming partly sunny. Isolated showers. Highs 68 to 89. Light winds becoming east up to 10 mph in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Lows 58 to 75. East winds up to 15 mph. Chance of rain 20 percent.

Wednesday: Partly sunny. Isolated showers in the afternoon. Highs 69 to 90. East winds 10 to 15 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

A surface trough east of the islands and a weak disturbance aloft will combine to keep trades light and the atmosphere a little more unstable over the next couple of days. Local daytime sea breezes will cause showers to favor interior and leeward sections during the afternoons and evenings. There will also be some windward and mauka showers as well, mainly during the nights and mornings. The trough and disturbance still start to move away on Wednesday, with drier, breezy trades making a gradual return from east to west later Wed into Thu. We expect locally windy weather Friday as high pressure develops to the north of the Aloha State. Trades will weaken over the upcoming holiday weekend.

Discussion

A surface trough just over 200 miles E and NE of PHNL passed buoy 51100 about 07z and the wind there has switched to the SE. The trough is moving slowly toward the W at about 8 mph. Even though moisture is quite limited with precipitable water (PW) of only about an inch at Lihue and 1.2 at Hilo, scattered showers ahead of the trough are being enhanced by a 700 mb low over the islands which has raised and weakend the usual tradewind inversion over the state. The late evening ASCAT pass showed a sizable area of light winds to the S and SE of the surface trough that should move over the Hawaiian Islands today. Thus, gentle trades will become sea breezes today for most areas.
The combination of the approaching surface trough and mid-level low overhead should lead to a fairly active convective pattern this afternoon despite somewhat limited moisture. This idea is supported by the high resolution guidance, which suggests active downpours will develop in the usual interior and leeward sections this afternoon. Most of these downpours should be brief, but have added a mention of locally heavy rain for the afternoon for the usual locales.
Afternoon convection will fade this evening and as the trough and mid-level low continue moving west and weaken. Behind the axis of the trough, the background flow will turn SE, but with local land breezes taking over in protected locations. Some interior and leeward areas will see at least partial clearing overnight, while the SE flow brings some clouds and showers. These will tend to favor windward and mauka sections, but some south shores might get some rainfall as well.
The SE flow will draw additional moisture up over the islands on Wed, even as mid level temperatures start to warm. The smaller islands will probably be in the wind shadow of the Big Island for most of the day, so additional afternoon convection and/or downwind convergence plumes should allow additional showers through much of the day. The trades will start to build back in later Wed, but won’t firmly take hold until Wed night or Thu.
Today through Wed, a sharpening tropical upper tropospheric trough or TUTT to our NW will continue to bring high level moisture up over the islands from the SW. Patchy cirrus clouds will stream over the islands leading to occasional high cloudiness. Initially this will be mainly thin and near the Big Island, but guidance shows this cirrus likely becoming thicker near Kauai and possibly Oahu later Wed into Thu, before shifting away to our W.
Definitively drier and more stable air return on breezy trades starting Thu. The trades may become locally windy on Fri as a 1028 mb high consolidates about 900 mi N of Honolulu near 34N 157W. Might have to keep an eye on Fri as a potential Red Flag Warning day with fire weather concerns if the dewpoints dry out enough. The high remains quasi-stationary and weakens after that, for trades to ease over the holiday weekend. The background flow may turn SE again around the islands by Labor Day if the models are correct.

Aviation

Land breezes have developed over the islands while very light trades continue to slowly push locally heavy showers and pockets of MVFR Windward Oahu. After sunrise, sea breeze development will shift the focus for showers and MVFR to leeward and interior areas. Over Windward Big Island, light winds will once again allow clouds and showers to shift well upslope from PHTO favoring dry weather and higher ceilings there. Land breezes will bring clearing tonight.

Marine

Little change to the forecast with the morning package. High pressure remains far to the north, along with a surface trough to the northeast. This combination will maintain a light trade wind pattern through tonight. The trough is expected to move westward, pass north of the islands, and be northwest of the islands Wednesday. This will allow the trade winds to build back over the region from E to W later on Wednesday and Thursday. Winds will likely be strong enough over the typical windier areas near Maui County and the Big Island Thursday to warrant Small Craft Advisories (SCA). The trade winds are expected to strengthen further Friday, which could support expanding the SCA to most, if not all, waters.
No significant swells are expected through the weekend. A series of small south and southeast swells will maintain small surf through the period. East shore surf will remain very small until trade winds increase during the second half of the week.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov