Weather Forecast

Maui Weather Forecast for September 22, 2021

September 22, 2021, 7:15 AM HST
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Photo Credit: Laila Reiss

West Side

Today: Breezy. Sunny with isolated showers. Highs 81 to 86. East winds 10 to 25 mph. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with scattered showers. Lows 67 to 74. East winds 10 to 20 mph. Chance of rain 50 percent.

Thursday: Breezy. Mostly sunny with isolated showers. Highs 82 to 87. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

South Side

Today: Sunny and breezy. Highs around 86. North winds up to 20 mph.

Tonight: Partly cloudy. Breezy. Isolated showers after midnight. Lows around 68. Northeast winds up to 20 mph. Chance of rain 20 percent.

ARTICLE CONTINUES BELOW AD

Thursday: Mostly sunny. Breezy. Highs around 87. Northeast winds up to 20 mph.

North Shore

ARTICLE CONTINUES BELOW AD

Today: Breezy. Mostly sunny with scattered showers. Highs 78 to 83 near the shore to around 67 near 5000 feet. East winds up to 25 mph. Chance of rain 40 percent.

Tonight: Breezy. Mostly cloudy with showers likely. Lows 66 to 72 near the shore to around 54 near 5000 feet. Southeast winds up to 20 mph. Chance of rain 70 percent.

Thursday: Partly sunny. Breezy. Showers likely in the morning, then scattered showers in the afternoon. Highs 79 to 84 near the shore to around 69 near 5000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Central Maui

ARTICLE CONTINUES BELOW AD

Today: Breezy. Mostly sunny with isolated showers. Highs around 85. Northeast winds 10 to 25 mph. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with isolated showers. Lows 66 to 71. East winds 10 to 20 mph. Chance of rain 20 percent.

Thursday: Breezy. Mostly sunny with isolated showers. Highs around 86. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Upcountry

Today: Sunny with isolated showers. Highs around 63 at the visitor center to around 59 at the summit. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with scattered showers. Lows around 49 at the visitor center to around 46 at the summit. East winds up to 20 mph. Chance of rain 50 percent.

Thursday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 65 at the visitor center to around 62 at the summit. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

East Maui

Today: Breezy. Mostly sunny with scattered showers. Highs 78 to 83 near the shore to around 67 near 5000 feet. East winds up to 25 mph. Chance of rain 40 percent.

Tonight: Breezy. Mostly cloudy with showers likely. Lows 66 to 72 near the shore to around 54 near 5000 feet. Southeast winds up to 20 mph. Chance of rain 70 percent.

Thursday: Partly sunny. Breezy. Showers likely in the morning, then scattered showers in the afternoon. Highs 79 to 84 near the shore to around 69 near 5000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Lanai City

Today: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs 74 to 83. Northeast winds 10 to 25 mph. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with isolated showers. Lows around 67. Northeast winds up to 20 mph decreasing to up to 10 mph after midnight. Chance of rain 20 percent.

Thursday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 74 to 83. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Kaunakakai

Today: Breezy. Mostly sunny with isolated showers. Highs 75 to 86. East winds 10 to 25 mph. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with isolated showers. Lows 60 to 71. East winds 10 to 20 mph. Chance of rain 20 percent.

Thursday: Breezy. Mostly sunny with isolated showers. Highs 75 to 86. East winds 10 to 20 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

High pressure north of the state will keep moderate to breezy trade winds in place through early next week. Rather dry conditions are expected this morning, with more typical trade wind weather featuring windward and mauka showers and the occasional leeward spillover returning later today through Saturday. A trough of low pressure sliding by south of the state could bring more unsettled conditions to windward areas, particularly over the Big Island and Maui, Saturday night into early next week.

Discussion

Currently at the surface, a ridge of high pressure around 650 miles north of Kauai, continues to drive moderate to breezy trade winds across the island chain early this morning. Infrared satellite imagery shows partly to mostly cloudy conditions in windward locales, with clear to partly cloudy skies in most leeward areas. Radar imagery shows a few light showers moving into windward sections of the Big Island, with very little if any shower activity across the remainder of the state. Main short term concerns revolve around trade wind trends and rain chances during the next few days.
The ridge of high pressure north of the islands should keep breezy trade winds in place today, with the trades then trending down to moderate levels tonight and Thursday as a cold front approaches and stalls out to the distant northwest. Moderate trade winds should then hold in place Friday and Saturday, before potentially becoming breezy again Sunday and Monday as a trough of low pressure passes by to the south of the state.
As for the remaining weather details, UW-CIMSS total precipitable water (PW) imagery shows a dry airmass over the smaller islands, with PW values of 0.9 to 1.1 inches. Slightly higher PW values of 1.1 to 1.3 inches are present over and upstream of the Big Island. This should translate into fairly dry conditions across much of the state this morning. The breezy trades will likely bring a few light showers into windward areas, with coverage the highest over windward Big Island. The airmass upstream of the islands should moisten begin to moisten up by late this afternoon, bringing a return to more typical trade wind weather. Bands of clouds and showers will then move through the islands tonight through Saturday, with showers favoring windward and mauka areas, particularly at night and during the early morning hours, with a few showers affecting leeward communities at times as well.
A surface trough sliding by south of the state could bring some more unsettled weather to windward areas Saturday night through Monday, particularly over windward sections of the Big Island and Maui. The latest 00Z ECMWF has trended further south with the surface trough position, and now is closely in line with the 00Z GFS solution. This suggests the deepest moisture associated with the trough, and potential for heavier rain, will remain to the south of the island chain. We will continue to keep a close eye on the model trends however, as only a slight deviation northward could bring some heavy rain into windward sections of the eastern islands late in the weekend into early next week.

Aviation

High pressure centered far north of the area is moving east slowly. The feature will sustain moderate to breezy trade winds across the island chain through today and beyond. Showers advancing on the trades will occasionally produce brief MVFR in lower ceilings and visibilities, mainly in windward and mauka sections statewide.
An AIRMET for mountain obscuration remains in effect for windward portions of the Big island. This AIRMET may need to be extended through late morning as more lower clouds and showers are approaching the isle from the east. Also, an AIRMET for moderate low level turbulence to the lee of the mountains has been extended, and will likely remain in place through this afternoon.

Marine

The northern Pacific has transitioned out of its summer mode featuring a pair of gale- to storm-force lows driving overlapping swells toward the islands this week. The first north-northwest swell is peaking above the predicted level early this morning at the nearshore PacIOOS buoy near Hanalei. Expect this trend to continue down the island chain through the morning hours today before gradually easing tonight through Thursday.
A larger north-northwest swell associated with a storm-force low, currently centered around 2000 miles to the northwest, should begin to fill in by Thursday night, peak Friday (surf may near the advisory levels along exposed north and west facing shores of the smaller islands), then slowly fade into the weekend. Recent satellite data reflected this with a decent sized area of gale /storm-force winds focused at the area within the 315 to 330 degree band (better energy focused northeast of the state). Altimeter data and SOFAR drifter buoys within/near the fetch showed seas ranging from 28 to 34 ft (slightly larger than guidance) yesterday evening and early this morning.
Surf along south facing shores will remain up into the second half of the week as a long-period south swell moves through. This event should peak around/by Thursday before fading into the weekend.
Surf along east facing shores will remain small and choppy due to the fresh/strong trades locally and just upstream of the state.
Small Craft Advisory winds will continue over the windier areas and channels from the Kaiwi Channel to the Big Island through the day today (may need to be extended into tonight). Seas will near the advisory-level of 10 ft Friday due to a combination of the aforementioned long-period north-northwest swell and seas associated with the trades.

Fire weather

A dry airmass in combination with the gusty trade winds and dry fuels will result in critical fire weather conditions today. As a result, a Red Flag Warning remains in effect through 6 PM this evening for leeward areas of most islands.

HFO Watches/Warnings/Advisories

Red Flag Warning until 6 PM HST this evening for Kauai Leeward, Oahu South Shore, Waianae Coast, Oahu North Shore, Olomana, Central Oahu, Waianae Mountains, Molokai Leeward, Lanai Makai, Lanai Mauka, Maui Leeward West, Maui Central Valley, Leeward Haleakala, Kona, South Big Island, Kohala.
Small Craft Advisory until 6 PM HST this evening for Kaiwi Channel, Maui County Windward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov

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