U.S. property insurers like Travelers Cos. Inc. and Chubb Corp. were expecting a relatively mild fourth quarter for catastrophe losses, but a series of punishing storms across the country in December may have blown away those estimates.

That could add more reason for investors to sell property insurance shares, already under pressure from a weak market, limited pricing power and depressed valuations.

Floods in Southern California, a blizzard in the Northeast and deadly tornadoes in the South lashed the country during the holiday season.

Add to that a storm in early October that roiled the Midwest and South and ranks as one of the five worst in the world for the year, and some of the more optimistic estimates may now be endangered.