For its part, Fitch says the losses from Hurricane Irene “are likely to be material, but manageable, for U.S. property and casualty insurers and reinsurance companies.”

Catastrophe modelers are estimating losses to be up to $6 billion on the high end and $1.5 billion at the low end.

Fitch notes that the $3 billion to $6 billion estimates place Irene on par with Hurricane Rita in 2005 and Hurricane Hugo in 1989.

When added to the losses suffered during the first half of the year, Irene “put further strain on the industry's underwriting results,” says Best, estimating first-half 2011 pre-tax catastrophe losses at $27 billion, based on a survey.

“A.M. Best does not anticipate a significant number of rating actions to be associated with Hurricane Irene,” the rating service says in its report. “However, companies with significant market share in the impacted states will be evaluated relative to A.M. Best's previous loss expectations” and “material deviations could lead to negative rating actions.”

The action could range from review to a downgrade.

Additional, sizable catastrophe losses from additional events could “lead to greater ratings vulnerability,” says Brian Schneider, a senior director at Fitch. Any rating action on a reinsurer or insurer “would depend on the size of the loss relative to capital, options pursued to replenish capital and underwriting prospects going forward,” he adds.