Hurricane Matthew is just off the east coast of Florida near Cape Canaveral, the National Hurricane Center said in an advisory on Friday, after killing hundreds of people in Haiti on its move north through the Caribbean.
Data modelling firm RMS told clients earlier this week its initial estimates were a 42 percent chance of a $20 billion insurance loss and a 26 percent chance of a $30 billion loss from the hurricane, a source familiar with the research said.
Ben Brookes, vice president capital markets at RMS told Reuters its guidance to clients was based on a single forecast, adding: "to project impact from this alone would be misleading".
"We have continued to update our guidance as the situation changes," Brookes said, without giving further details.
An estimate from Kinetic Analysis of insured losses of $25 billion would make Matthew "the second most costly hurricane in U.S. history behind Katrina", JPMorgan analysts said in a note late Thursday, referring to the hurricane which hit New Orleans and the surrounding coast in 2005.
A Kinetic Analysis spokesman said its $25 billion estimate was made on Thursday and its current estimate was "considerably lower", without giving further detail.
Market participants were keeping a close track on the hurricane's movements.
"People are looking at this literally every minute and working overnight on it," one trader said.
The average impact to U.S. property and casualty insurers' book value from $10-30 billion of insured losses from the hurricane would equate to around a quarter's worth of earnings, the JPMorgan analysts added.
Heritage Insurance Holdings gave a preliminary loss estimate on Friday of around $500 million.
A $20 billion insured loss would match the insured losses caused by Hurricane Sandy in the northeast of the United States in 2012, which did not make landfall. A loss of this size would lead to "material risks" for Lloyd's of London insurers, analyst Ben Cohen at Canaccord Genuity said in a note on Friday.