Irma affected more than 90% of Florida's mortgaged properties

More than 90% of all mortgaged properties in Florida are in a FEMA-designated disaster area following Hurricane Irma, nearly three times the number impacted by Hurricane Harvey, according to Black Knight.

"While the total extent of the damage from Hurricane Irma is still being determined, it is clear that the size and scope of the disaster is immense," Ben Graboske, Black Knight data & analytics executive vice president, said in a press release.

"Indeed, in terms of the number of mortgaged properties and their associated unpaid principal balances, Irma significantly outpaces even the number of borrowers impacted by Hurricane Harvey."

"More than 3.1 million properties are now included in FEMA-designated Irma disaster areas, representing approximately $517 billion in unpaid principal balances. In comparison, Harvey-related disaster areas held 1.18 million properties — more than twice as many as with Hurricane Katrina in 2005 — with a combined unpaid principal balance of $179 billion," Graboske said.

There were 456,000 mortgaged properties in the Hurricane Katrina disaster area, with an unpaid principal balance of $46 billion.

Over one-quarter of the mortgage borrowers whose properties were in areas affected by Hurricane Harvey could miss at least one loan payment over the next four months, Black Knight previously said.

That analysis was based on the experience following Hurricane Katrina, where like Hurricane Harvey, the majority of the damage was flood related. Black Knight did not do a similar analysis with Irma because most of the damage was wind-related, a Black Knight spokesman explained.

One bright spot for mortgage lenders is that Irma did not directly pass over Puerto Rico and therefore did not cause the level of damage it did on other Caribbean islands.

"From a mortgage performance perspective, this was particularly good news, as delinquencies there were already quite high leading up to the storm. At more than 10%, Puerto Rico's delinquency rate is nearly three times that of the U.S. average, as is its 5.8% serious delinquency rate," said Graboske.

"In contrast, the disaster areas declared in Florida have starting delinquency rates below the national average, providing more than a glimmer of optimism as we move forward."