About 10 percent of Darien residents and 30 percent of Stmaford residents were without power as of 4 p.m. Tuesday, due to problems at the Glenbrook Substation, according to CL&P spokesman Mitch Gross.

The afternoon outage is completely unrelated to this morning's outage, which left more than 400 Darienites without power, Gross said.

"It's a high-demand day," Gross said. He said the power company does not yet have an estimate on when power will be restored to the 771 Darienites and 16,736 Stamfordites in the dark.

The National Weather Service issued a heat advisory for Tuesday afternoon, which states that the combination of high temperatures and gradually increasing humidity will result in a heat index between 100 and 104 degrees.

There are currently several cooling stations open in town, including Town Hall, the senior center at 30 Edgerton St. and the YMCA Post Road, which is also offering showers for those without power.

"The biggest concern from a public health standpoint is senior citizens, who are a vulnerable population," said Darien Police Sgt. Jeremiah Johnson Tuesday morning. "Some may be reluctant to leave their homes, but we're hoping that especially today, they'll seek relief at the cooling centers.

"If anyone has elderly or disabled residents or neighbors, it's a good thing to check on them," Johnson said.