A pair of wildfires merged Sunday as firefighters fought back flames near a mountaintop observatory and nearly 100 summer homes in southeastern Arizona.

Hail and rain fell around the Mount Graham International Observatory (search), aiding the battle to tame the fires. But lightning started a new blaze Saturday in the steep terrain on the mountain's south side.

The biggest fires on the mountain, the lightning-sparked Nuttall and Gibson fires, had joined but were 55 percent contained, firefighters said. They have charred 29,000 acres on Mount Graham (search) since they began in late June.

More thunderstorms were possible Sunday and there was an increased chance of rain Monday and Tuesday.

"If weather patterns hold as they are, everything will be winding down," fire spokesman Kent Romney said.

Fire officials were concerned about possible flooding in mountainside canyons because the fires stripped vegetation that ordinarily would be able to absorb the rain.

Crews had been able to protect the observatory and mountain communities of Turkey Flat and Columbine. Bulldozers cleared out vegetation in a 200-foot-wide ring around the observatory, home of some of the world's most advanced telescopes.

Fire managers did not know when evacuated residents would be able to return.

"You never want to say that you are 100 percent sure that everything is safe, but we are feeling real good," said Paul Summerfelt, deputy incident commander for the firefighting team.

The fires damaged the steps of a lookout tower and destroyed a building containing communication equipment. Fire officials said fighting the blaze had cost $8 million as of Sunday.