The large eye of the storm containing calm air passed directly over the tiny island chain of 65,000 inhabitants on Friday, reducing the time the British territory was exposed to hurricane-force winds and limiting potential damage, AIR said in its estimate, which was released late Wednesday.
EQECAT, another modeling firm, estimated the insured losses at $300 million, according to a report on Monday by Insurance Journal, a trade publication.
Gonzalo blew off portions of roofs and caused structural damage to some older buildings, including some historical structures, AIR found in a survey conducted Sunday and Monday.
But the company found that more modern and well-maintained buildings constructed under strict new building codes to withstand sustained wind speeds up to 110 mph and gusts up to 150 mph held up well. Most resorts saw little more than minimal damage to roofs, AIR reported.
Gonzalo followed Tropical Storm Fay by a week, while some damaged roofs were still under repair.
The hurricane hit the Atlantic island archipelago off the coast of North Carolina with maximum sustained winds of around 110 miles per hour, forecasters said.
Gonzalo was the strongest storm to strike Bermuda since the similar-sized Hurricane Fabian in 2003, which AIR said caused $300 million in damage. A repeat of Fabian this summer would have cost $650 million, factoring in increased 2014 insurance exposure, AIR said.
The islands also suffered wide power outages and blocked roads, but there were no fatalities. Power has mostly been restored to customers, Bermuda Electric Light Co said on Thursday.
AIR's calculations do not include damage to infrastructure or boats tossed at sea and blown from berths on land.
Earlier, Gonzalo hit elsewhere in the Caribbean, tearing off roofs in Antigua and killing an elderly sailor and damaging some three dozen vessels in St. Maarten.
After departing Bermuda, Gonzalo stayed offshore but brought tropical storm conditions to Newfoundland, Canada, on Sunday, and battered northern Scotland on Tuesday.