Weather Forecast

Maui Weather Forecast for September 16, 2021

September 16, 2021, 7:15 AM HST
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Photo Credit: Jeni Ji Cousins

West Side

Today: Partly sunny in the morning then becoming mostly sunny. Breezy. Isolated showers. Highs 79 to 90. East winds up to 20 mph increasing to 10 to 25 mph in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Isolated showers. Lows 71 to 78. East winds 10 to 25 mph. Chance of rain 20 percent.

Friday: Breezy. Partly sunny with isolated showers. Highs 80 to 91. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

South Side

Today: Mostly sunny. Highs around 89. Northwest winds up to 10 mph shifting to the northeast in the afternoon.

Tonight: Breezy. Partly cloudy in the evening, then mostly cloudy with isolated showers after midnight. Lows 70 to 77. North winds up to 20 mph. Chance of rain 20 percent.

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Friday: Partly sunny. Breezy. Isolated showers in the morning. Highs around 90. North winds 10 to 20 mph. Chance of rain 20 percent.

North Shore

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Today: Breezy. Partly sunny with scattered showers. Highs 76 to 85 near the shore to around 67 near 5000 feet. East winds 10 to 25 mph decreasing to up to 25 mph in the afternoon. Chance of rain 40 percent.

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then scattered showers after midnight. Lows around 73 near the shore to 51 to 56 near 5000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Friday: Breezy. Mostly cloudy with scattered showers. Highs 78 to 85 near the shore to around 67 near 5000 feet. East winds 15 to 20 mph. Chance of rain 50 percent.

Central Maui

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Today: Mostly sunny. Breezy. Highs 82 to 89. East winds up to 25 mph increasing to 10 to 25 mph in the afternoon.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Isolated showers. Lows 70 to 75. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Friday: Partly sunny. Isolated showers in the morning. Highs 82 to 89. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Upcountry

Today: Breezy. Mostly sunny with isolated showers. Highs around 60 at the visitor center to around 56 at the summit. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Scattered showers. Lows 46 to 57. East winds up to 20 mph. Chance of rain 50 percent.

Friday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 63 at the visitor center to around 60 at the summit. East winds 15 to 25 mph. Chance of rain 40 percent.

East Maui

Today: Breezy. Partly sunny with scattered showers. Highs 76 to 85 near the shore to around 67 near 5000 feet. East winds 10 to 25 mph decreasing to up to 25 mph in the afternoon. Chance of rain 40 percent.

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then scattered showers after midnight. Lows around 73 near the shore to 51 to 56 near 5000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Friday: Breezy. Mostly cloudy with scattered showers. Highs 78 to 85 near the shore to around 67 near 5000 feet. East winds 15 to 20 mph. Chance of rain 50 percent.

Lanai City

Today: Partly sunny in the morning then becoming mostly sunny. Highs 74 to 83. East winds up to 15 mph.

Tonight: Breezy. Partly cloudy in the evening, then mostly cloudy with isolated showers after midnight. Lows around 66. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Friday: Partly sunny. Breezy. Highs 73 to 81. East winds 10 to 20 mph.

Kaunakakai

Today: Partly sunny in the morning then becoming mostly sunny. Breezy. Highs 69 to 90. East winds 10 to 20 mph.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Isolated showers. Lows 59 to 76. East winds 15 to 25 mph. Chance of rain 20 percent.

Friday: Partly sunny. Breezy. Isolated showers in the morning. Highs 69 to 90. East winds 15 to 25 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Unsettled weather will linger mainly over the western islands of Kauai and Oahu today as we transition to a more stable weather pattern. High pressure will build in east of the low as it moves away from the state with strengthening trade winds and drier trends into Sunday. Brief passing showers will develop over the typical windward and mountain areas of each island. Another upper level disturbance may bring increasing showers along with decreasing trade wind speeds from Sunday into early next week.

Discussion

An unstable upper level low, just northwest of Kauai, will continue to drift westward away from the island chain. Lingering instability will keep passing showers over the western islands through the morning hours. Local radar imagery this morning shows a few bands of moderate to heavy showers drifting through the coastal waters from Maui to Kauai. While strengthening easterly trade winds are bringing more stable conditions to the Big Island this morning. The heaviest showers last night were reported over the eastern and southeastern slopes of the Big Island with rainfall totals ranging from 1.00 to 3.00 inches over a six to twelve hour time period. A Flood Advisory was issued for this area to cover minor nuisance flooding concerns.
Today will be a transition day from unstable wet weather with light winds into drier weather trends with strengthening trade winds as the high pressure system north of the islands builds back into the region. Trade winds will strengthen into the moderate to locally breezy range for most areas by afternoon. As the upper low drifts away from the islands a mid level (700 mb) ridge will move into the region from east to west and stabilize the air mass. Forecast guidance suggests trade wind inversion heights dropping down to the 5,000 to 7,000 foot range later this evening, producing fairly stable and dry weather across the state. After some enhanced morning showers, locally heavy at times near Kauai, we will transition into brief passing showers focused mainly over windward and mountain areas.
Friday and Saturday, a high pressure system north of the islands will produce moderate to breezy trade winds with fairly stable and dry weather conditions. Brief passing showers are possible mainly over windward and mountain areas.
Sunday into Tuesday, a weak upper level trough will move into the region from the east, increasing shower trends for all islands with decreasing trade wind trends from Sunday night into early next week.

Aviation

The surface trough should be exiting Kauai County in the next couple of hours, with a east-southeast wind flow following right behind. A trade wind flow, now over the Big Island, will be spreading westward, reaching Oahu around noon, then Kauai late this afternoon. The return of the trades will be moderate to locally strong, as high pressure strengthens north of the islands, leading to an AIRMET Tango by 22z for low level turbulence, south through west of all mountains.
The area of clouds and showers that impacted eastern and windward Big Island continues to break up, resulting in an area of layered clouds between 10k and 25k feet, now moving westward across Maui County. It will continue westward reaching Oahu before sunrise, then dispersing as the morning progresses. There are some lower clouds and showers that will favor the windward and mountain areas of Maui, Molokai, and Oahu during the morning hours, but not widespread enough to warrant an AIRMET Sierra for mountain obscuration.
AIRMET Sierra for eastern and windward Big Island is likely to be lowered at 16z.
Lingering instability and moisture will impact primarily interior and leeward Kauai this afternoon, leading to potential AIRMET Sierra and mountain obscuration. Otherwise, we are looking at the the return of a typical trade wind pattern.

Marine

A surface trough northwest of Kauai is moving west away from the islands this morning. This trough’s exit will allow high pressure north of the state to build down toward the eastern waters and tighten the regional pressure gradient. This will ultimately re- establish primarily fresh to locally strong trades trades the next several days. A Small Craft Advisory (SCA) is in effect for the Kaiwi Channel eastward, including the waters surrounding Maui and Big Island, except for Maalaea Bay. Weakening trades over the windward Big Island waters and a late day strengthening of Maalaea Bay northerlies to advisory thresholds will be the only areal adjustment needed to tonight into Friday’s SCA.
The most recent southwest to south swell will be slowly falling through today with a possible small reinforcement filling in later today into early Friday. The next small southwest south swell may arrive toward the middle of next week. A small, medium period northwest swell is expected to reach the islands later this weekend to then be followed by a series of small, similar to slightly higher period northwest north swell energy through next week. East facing shore surf will trend up to seasonable levels the next couple of days with the return of fresh trades over and upstream of the state.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Saturday for Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.
Small Craft Advisory until 6 PM HST this evening for Big Island Windward Waters.
Small Craft Advisory from 6 PM this evening to 6 AM HST Saturday for Maalaea Bay.

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Data Courtesy of NOAA.gov

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