Despite U.S. insured losses estimated as high as $6.6 billion, Hurricane Irene, which later became Tropical Storm Irene as it drenched the Northeast, added to already extensive catastrophe-related losses this year but was not a market-changing event, experts say.

Irene became a hurricane late last month as it left Puerto Rico. It did an estimated $500 million in damage in the Caribbean and the Bahamas as a Category 3 hurricane, according to estimates by Aon Benfield Inc.

It weakened to a Category 1 before making landfall in North Carolina. Then as a tropical storm, it dropped heavy rain along much of the East Coast and particularly the Northeast, resulting in extensive flooding.

Flooding issues continued in the Northeast last week as heavy rain moved through the area.

Irene killed at least 46 people in the U.S., caused power outages affecting some 8 million people and damaged tens of thousands of buildings, but losses were less than had been feared as the storm approached the United States, Aon Benfield, the reinsurance unit of Chicago-based broker Aon Corp., said in a statement. It estimated that U.S. insured losses would range from $1.6 billion to $6.6 billion.

Boston-based catastrophe modeler AIR Worldwide estimated Irene's insured losses at $3 billion to $6 billion. Oakland, Calif.-based EQECAT Inc. estimated insured losses at $1.5 billion to $2.8 billion. Newark, Calif.-based Risk Management Solutions has not yet estimated losses from Irene.

Rating agencies said the storm should not be a major capital or credit event for property/casualty insurers.

“It's not a monumental loss issue that'll change the dynamics of the industry,” according to Meyer Shields, an analyst for Baltimore-based Stifel, Nicolaus & Co. Inc.

Major homeowner property insurers operating in the Northeast—such as Northbrook, Ill.-based Allstate Corp., New York-based Travelers Cos. Inc. and Boston-based Liberty Mutual Group Inc.—likely will bear the brunt of losses related to the storm, analysts say.

“This is a manageable exposure for the Hartford,” a spokesman for Hartford, Conn.-based The Hartford Financial Services Group Inc. said in an email.

A spokesman for Fireman's Fund Insurance Co. said it was too soon to tell how much the Novato, Calif.-based insurer would pay in claims, but said claims had been received from all states hit by Irene, mainly homeowners.

As far as commercial losses, Matthew Nielsen, senior product manager at RMS in Newark, Calif., said a team from the firm saw hotels in Virginia Beach, Va., that suffered business interruption and broken windows, requiring some repairs. “For commercial (insureds), that's as bad as it got,” he said.

Bob O'Brien, managing director of Marsh Inc.'s national property claims practice, said about 200 claims had been filed by businesses, including health care organizations, hospitality and retail firms, educational institutions and municipalities. Most were affected by service interruptions and flooding, he said.

Al Tobin, managing principal and national property practice leader for Aon Risk Solutions in New York, said potential losses from power outages appeared to be greater than building damage, noting that “everybody was superprepared for Irene.”

“On its own, Irene wouldn't have an impact on prices,” said David Paul, a principal at ALIRT Insurance Research L.L.C. in Windsor, Conn.

But the storm did expand already extensive losses this year due to disasters in Japan, New Zealand, the United States and elsewhere. On Friday, Swiss Reinsurance Co. Ltd. estimated first-half insured losses were $70 billion, making it the second-most expensive insured loss year since 2005.

“This year is wearing away at the psychology of (insurance) underwriters,” Mr. Paul said.