PRESCOTT, Ariz.- An elite squad of 19 Arizona firemen killed in the worst U.S. wildland firefighting tragedy in 80 years apparently was outflanked by wind-whipped flames in seconds, before some could scramble into cocoon-like personal shelters.

Details of Sunday's deaths of all but one member of a specially trained, 20-man "Hotshots" team remained vague a day after they perished in a blaze that destroyed scores of homes and forced the evacuation of two towns in central Arizona.

But fragments of the firefighters' final moments painted some of the picture as investigators launched a probe into exactly how the disaster unfolded.

Fire officials said the young men fell victim to a highly volatile mix of erratic winds gusting to gale-force intensity, low humidity, a sweltering heat wave and thick, drought-parched brush that had not burned in some 40 years.

The deaths brought an outpouring of tributes from political leaders, including U.S. President Barack Obama, who is on an official trip to Africa.

Arizona Governor Jan Brewer called the deaths "one of our state's darkest, most devastating days" and ordered state flags flown at half staff from Monday through Wednesday.

The blaze was sparked on Friday by lightning near the town of Yarnell, about 80 miles (128 km) northwest of Phoenix. It was still raging unchecked on Monday after scorching some 8,400 acres (3,400 hectares) of tinder-dry chaparral and grasslands.

Still, conditions faced by the "Hotshots," who fight flames at close range with hand tools, were typical for the wildfires they are trained to battle, fire officials said.

They were trapped as a wind storm kicked up and the fire suddenly exploded on Sunday, said Peter Andersen, a former Yarnell fire chief who was helping the firefighting effort.

"The smoke had turned and was blowing back on us," Andersen said. "It looked almost like a smoke tornado, and the winds were going every which way."

The powerful gusts abruptly split the fire, driving it in two directions, then pushing flames back in on the Hotshot crew, who were working on one flank of the fire front, he said.