Severe thunderstorms and heavy rain hit Maui on Friday, cutting off power for about 21,000 customers for several hours and forcing at least nine public schools to close.

Radar showed severe thunderstorms at 5:23 a.m., with storms spreading from Waikapu to Kaupo, moving southwest at 10 mph, according to the National Weather Service.

Wind gusts of up to 70 mph were reported, “posing significant risks to trees, roofs and outbuildings,” federal weather officials cautioned Friday.

They described the situation as dangerous, with “widespread wind damage likely across the island.”

Communities in Kahului, Honokohau, Haliimaile, Kipahulu, Wailuku, Maka­wao, Paia, Keokea, Olowalu, Wailea, Waihee and Kaanapali were warned of incoming heavy weather and urged to prepare.

On Friday afternoon county officials asked residents and visitors to conserve water until the water treatment facilities can “return to normal operating capacity.”

“Recent rain events have caused an increase in mud, sediment and turbidity in the surface water sources in West Maui, limiting production capacity of potable water at treatment facilities,” according to a statement from the county Department of Water Supply.

The water conservation request applies to the communities from Leialii Parkway to Puamana subdivision and includes Lahainaluna High School and areas below the campus.

The Maui Emergency Management Agency was partially activated after the severe weather and flash flood warning.

Starting at about 4 a.m. Friday, the storms brought high winds, several inches of rain, lightning, thunder and flooding to parts of Maui.

NWS lifted the warnings by 8 a.m. Friday.

At the start of the storm, about 21,000 Hawaiian Electric customers lost power. About 16,000 had electricity by noon Friday.

“Damage assessments and line inspections by ground and helicopter are currently taking place before power can safely be restored to the remaining 5,000 customers,” read a statement from Hawaiian Electric.

Some in communities in South Maui, Kula and West Maui were still without electricity Friday night due to storm-related outages. About 100 customers were still without power by about 9 p.m., according to a social media post by the company.

Federal weather officials also issued a winter weather advisory until noon Friday for Haleakala’s summit after reports of 70 mph winds and icy conditions.

Haleakala National Park’s website Friday morning warned readers that the Summit District was closed at the entrance due to icy conditions, according to a statement from county officials.

The hazardous conditions moved the state Department of Education to close schools in East, South and West Maui to students and staff.

Hana High & Elementary, Kamalii Elementary, Kihei Elementary, Lokelani Intermediate, Kulanihakoi High, King Kamehameha III Elementary, Princess Nahienaena Elementary, Lahaina Intermediate and Lahainaluna High closed Friday, according to a DOE spokesperson.

The schools notified families directly.

Okolani Drive and South Kihei Road, from Wailea Alanui Drive to Kilohana in South Maui, were closed as of noon Friday due to “storm impacts,” according to a statement from the county Department of Public Works.

“Also, trees are blocking both lanes on Naalae and Waipoli roads Upcountry, and crews are working to clear the roads,” read the statement. “Other County roads and highways that closed due to storm impacts this morning reopened by noon Friday.”

The county Department of Parks and Recreation closed the following parks and facilities due to debris, damage and power outages from the thunderstorm:

The rain forced the Central Maui Regional Sports Complex and the Coach Spencer Shiraishi Memorial Pool to close in Central Maui.

The Keawakapu Beach parking lot, Kihei Aquatic Center and Kihei Community Center closed in South Maui.

The new Kula Ballfield Park’s restrooms will “remain closed this weekend due to a main water line break,” but portable restrooms will be made available, officials said.

Just how long the county facilities will be closed due to storm damage “will be provided as damage assessments are made,” according to the county.

Permitted facilities also may be affected, according to the county Department of Parks and Recreation. Permit holders were “directly notified of impacts.” Various department buildings lost phone service at about noon Friday.

Maui residents could see “scattered showers, mainly before noon” today, which could be mostly sunny, with a high near 71, and winds moving east and northeast at about 18 to 25 mph.

Gusts as high as 36 mph could blow through Maui today, the weather service forecast Friday night, with about a 30% chance of rain.