Hurricane Irma and Harvey are set to exceed New Orlean's Hurricane Katrina as the most expensive insured loss event in history.
Bronek Masojada, chief executive of Hiscox Insurance group, said the impact of Irma and Harvey cumulatively means that the cost is likely to exceed the damage caused in the 2005 disaster.
Katrina devastated New Orleans and is widely regarded as the most expensive insured loss event in the history of insurance anywhere in the world, costing about £200bn.
Mr Masojada says that in recent years there has been a "big variability" in the number of hurricanes, which are often "more intense".
"We do not sell insurance for a decade but for a year, and we can adjust as new information and new science become apparent," he told the BBC.
Mr Masojada says that in Florida building codes are especially important because they tell insurers when a home or building was constructed, giving a better idea as to the probability of it being hit by a hurricane.
Hurricane Irma has ripped through central Florida - killing at least five, leaving millions of homes without power and flooding city streets.
Irma, ranked as one of the most powerful hurricanes recorded in the Atlantic, came ashore on Sunday and battered towns up and down the heavily-populated state.
The storm weakened to a Category 1 hurricane on Monday morning, carrying maximum sustained winds of about 85mph by 2am local time (6am GMT).
Ferocious winds were churning northwest in the centre of the state - near the Tampa and Orlando metro areas - on Monday morning, the National Hurricane Center said.
Monroe County, which includes the Florida Keys, has reported two deaths, while Hardee County has also reported two deaths so far and one person died in a crash in Orange County.
The storm killed at least 28 people as it raged westward through the Caribbean en route to Florida, devastating several small islands and grazing Puerto Rico, the Dominican Republic and Haiti before pummelling parts of Cuba's north coast with 36-foot waves.
Irma was ranked a Category 5, the rare top end of the scale of hurricane intensity, for days and its ferocity as it bore down on hurricane-prone Florida prompted one of the largest evacuations in US history.
Some 6.5 million people, about a third of the state's population, had been ordered to evacuate southern Florida.
Residents fled to shelters, hotels or relatives in safer areas.
On Sunday, Irma claimed its first US fatality - a man found dead in a pickup truck that had crashed into a tree in high winds in the town of Marathon, in the Florida Keys.
Jonathan Brubaker, 51, waited out the storm bunkered in a recently constructed house in Bradenton, on the state's west coast south of Tampa, with hurricane shutters drawn, flashlights and candles ready.
As a radar app on his phone showed Irma passing by, he had seen little more than gusty winds. He still had power.
"I feel like we kind of dodged bullet on this one,'' he said, adding that he would wait until Monday morning before trying to sleep. "And then, I think we're OK, knock on wood."
High winds snapped power lines and left about 4.5 million Florida homes and businesses without power in the state, whose economy represents about 5 percent of US gross domestic product.
Irma was forecast to continue churning northward along Florida's Gulf Coast during Monday morning, further weakening along the way before diminishing to tropical-storm status over far northern Florida or southern Georgia later in the day.
It could dump as much as 25 inches of rain in parts of Florida and as much as 16 inches in parts of Georgia, prompting flash flood and mudslide warnings, the National Hurricane Center said.
Local TV news video of damage in Naples, a city on the Gulf coast about 125 miles (200 km) to the northwest of Miami, showed buildings ripped apart by hurricane winds and streets flooded by rain and storm surges.
The storm's westward tilt to Florida's Gulf Coast spared the densely populated Miami area the brunt of its wrath, although the wide reach of the hurricane meant the state's biggest city was still battered.
Miami apartment towers swayed in the high winds, three construction cranes were toppled, and small white-capped waves could be seen in flooded streets between Miami office towers.
Waves poured over a Miami seawall on Sunday, flooding streets waist-deep in places around Brickell Avenue, which runs a couple of blocks from the waterfront through the financial district and past foreign consulates.
High-rise apartment buildings were left standing like islands in the flood.
"We feel the building swaying all the time," restaurant owner Deme Lomas said in a phone interview from his 35th-floor apartment. "It's like being on a ship."
Police in Miami-Dade County said they had made 29 arrests for looting and burglary. "We're on patrol and won't tolerate criminal activity as our community recovers from Hurricane Irma," it said on its Twitter.
The storm and evacuation orders caused major disruption to transportation in the state that is a major tourist hub.
Thousands of flights were cancelled.
Miami International Airport, one of the busiest in the country, halted passenger flights through at least Monday and will see if it can resume those operations on Tuesday.
Irma, which was expected to cause billions of dollars in damage to the third most populous US state, hit just days after the Houston area was deluged by unprecedented flooding from Hurricane Harvey, which dumped more than 50 inches of rain in parts of Texas.
Harvey killed at least 60 people and caused an estimated £136 billion in property damage.
US President Donald Trump, acting at the governor's request, approved a major disaster declaration for Florida on Sunday, freeing up emergency federal aid in response to Irma, which he called "some big monster".