(Adds detail, CEO and CFO comment, share price)
LONDON, Nov 2 (Reuters) - Hurricanes blew insurer RSA's underwriting performance off course in the third quarter as it set aside an initial 50 million pounds ($66 million) for weather losses in the United States and the Caribbean.
Hurricanes Harvey, Irma and Maria have caused more than $100 billion in insured losses in the region in recent weeks, hitting the performance of insurers and reinsurers.
Swiss Re and Lancashire reported losses on Thursday as a result of the hurricanes and other recent natural catastrophes.
"Claims notifications for these (hurricane) events are still developing, and we expect this (50 million pound) provision to increase somewhat," RSA said in a statement, adding that as a result, "group underwriting results are. ..slightly weaker than prior year".
It did not give profit figures in its third-quarter trading statement, but said group profits were ahead of last year, though by less than it had targeted.
RSA's shares were down 1.9 percent at 620.5 pence at 0830 GMT, making it one of the worst performers in the FTSE 100 index .
Best known in Britain for its More Than brand, RSA also has major businesses in Canada, Ireland and Scandinavia.
RSA, which also offers international insurance through its UK division, was not expecting "material losses" from wildfires in California or earthquakes in Mexico, Chief Executive Stephen Hester told a media call.
Its losses from Storm Ophelia, which hit Ireland last month, would likely be less than 5 million euros ($5.82 million), Hester added.
RSA could suffer further large losses totalling around 20 million pounds in the fourth quarter before its reinsurance cover kicks in, Chief Financial Officer Scott Egan told the call.
RSA posted net written premiums of 5.1 billion pounds for the first nine months, up 8 percent on a year earlier.
Tangible equity stood at 2.81 billion pounds as of Sept 30, up 0.7 percent from 2.79 billion at the end of the June quarter. ($1 = 0.7531 pounds) ($1 = 0.8592 euros) (Reporting by Carolyn Cohn; editing by Jason Neely/Keith Weir)