September has seen a brutal string of days with temperatures topping 105 in the Fresno area, with Tuesday’s forecast high of 113 setting a new all-time record.

The previous record of 111 was already matched on Sept. 2.

Tuesday’s hot temperatures are expected to peak between 3 p.m. and 5 p.m.

California’s Independent System Operator, or ISO, announced Tuesday afternoon that rolling outages might have to be implemented later Tuesday to prevent cascading blackouts. The ISO, which oversees the power grid, declared an Energy Emergency Alert 2, which allows the agency to buy more energy while offering financial incentives to cut energy use.

ISO estimates that Tuesday’s electricity demand will top 52,000 megawatts, a new historic all-time high.

The agency is expected to declare an EEA 3 around 5:30 p.m., one step away from ordering rotating power outages. If outages become necessary, utility companies will send out phone, text, or email messages to customers notifying them of outage areas and likely durations.

High temperatures in the triple digits are forecast to continue through the week, but there may be some relief in sight, National Weather Service meteorologist J.P. Kalb said Tuesday.

The high pressure ridge over the Great Basin that has held steady since mid-August, holding a heat dome over California, will begin to weaken after Tuesday. Meanwhile, a trough of low-pressure air will start to push in from the Pacific, thanks to Hurricane Kay, bringing moisture and on-shore breezes that will cause the high temperatures to drop into the upper 90s by this weekend, Kalb said.

Emergency Generators Activated

California’s extreme heat is putting a huge strain on the power grid. The ISO has called for Flex Alerts on a daily basis since last week, including one for Tuesday, asking Californians to use as little power as possible between 4 p.m. and 9 p.m.

On Monday the ISO requested that four emergency power generators in Roseville and Yuba City be started up to augment the power supply.

The Department of Water Resources, which operates the generators, said they could provide an additional 120 megawatts to the state’s power supply, or enough to power 120,000 homes.

It was the first time the natural gas-powered generators were fired up since they were installed last year, the department reported.

California will need a lot of power to keep the lights on for the next few days. The excessive heat advisory that puts the entire Valley into “magenta” is the first time for such a widespread heat alert across the region since 2006, Kalb said.

That heat wave, which hit in July, caused hundreds of deaths in the Valley and across the state. Even with the availability of cooling centers, Fresno’s hospitals were strained by the number of people with heat-related illness.

Why So Hot Now?

Kalb said the current heat wave is hitting now because monsoonal weather in July and August kept the heat from building up in the West. But once that ended, the heat dome drew from the heat that accumulated on sun-baked land in the West, raising both the daytime and nighttime highs.

“We had a lot of moisture in July and August, which is why we didn’t get to the peak earlier,” he said.

City of Fresno cooling centers and community centers are open until 7 p.m.:

Frank H. Ball, 760 Mayor Ave.; Ted C. Wills Community Center, 770 N. San Pablo Ave.; Mosqueda Community Center, 4670 E. Butler Ave.; Pinedale Community Center, 7170 N. San Pablo Ave.; Dickey Youth Development Center, 1515 E. Divisadero St.; Einstein Neighborhood Center, 3566 E. Dakota Ave.; El Dorado Neighborhood Center, 1343 E. Barstow Ave.; Fink-White Neighborhood Center, 535 S. Trinity St.; Highway City Neighborhood Center, 5140 N. State St.; Holmes Neighborhood Center, 212 S. First St.; Inspiration Park, 5770 W. Gettysburg Ave.; Lafayette Neighborhood Center, 1516 E. Princeton Ave.; Mary Ella Brown Community Center, 1350 E. Annadale Ave.; Maxie L. Parks Community Center, 1802 E. California Ave.; Melody Neighborhood Center, 5935 E. Shields Ave.; Quigley Neighborhood Center, 808 W. Dakota Ave.; Romain Neighborhood Center, 745 N. First St.; Sunset Neighborhood Center, 1345 W. Eden Ave.;

In the city of Clovis, the Police and Fire Headquarters and Sierra Vista Mall are open as cooling centers.

Public transit is free to people going to cooling centers.

Sites also are open in Coalinga, Firebaugh, Fowler, Huron, Kerman, Kingsburg, Mendota, Orange Cove, Parlier, Reedley, Sanger, and Selma.