Total insured losses from recent storms and tornadoes that swept through the U.S. South and Southeast are estimated at $3.7 billion to $5.5 billion, catastrophe modeler AIR Worldwide Corp. said Monday.

From April 22 to April 28, the National Weather Service recorded 550 eyewitness reports of tornadoes in 14 states. The most tornadoes hit in a four-day stretch beginning April 25.

In Alabama, the worst-hit of the affected states, the American Red Cross estimated at least 5,000 properties were destroyed in Tuscaloosa, which was hit April 27 by an EF-4 tornado that left an 80-mile-long trail of destruction. The state's insurance commissioner has indicated that total property losses could rival those of Hurricane Ivan in 2004.

‘Reduced to rubble'

“In areas of Tuscaloosa affected by the EF-4 tornado, large commercial structures were reduced to rubble,” Tim Doggett, principal scientist at AIR, said in a statement. “Many properties closer to the periphery of the tornado sustained significant damage to their roofs and openings (large plate glass windows and doors). With the building envelope breached, many sustained subsequent structural damage.”

The Mississippi Emergency Management Agency reported as many as 2,527 homes and 104 businesses were damaged, with 993 homes and 62 shops destroyed or badly damaged. In Virginia, state officials estimated that 443 buildings damaged, 137 of which were destroyed.

The death toll from the storms is believed to be 354 in seven states, making the event the second-deadliest storm outbreak in recorded U.S. history, AIR said in the statement.

AIR assessing buildings

After rescue efforts had largely ceased last week, AIR sent a survey team to areas in and near Tuscaloosa and Birmingham to assess building performance, wind speeds and damage. The team also surveyed Cullman, 50 miles north of Birmingham, where much of the city’s historic district was flattened by an EF-4 tornado. Pratt City and Pleasant Grove—two Birmingham suburbs most severely affected by the same EF-4 tornado—also were surveyed.

“As one would expect from a tornado of this strength, the damage in these mostly residential areas was near total along the direct path, leaving only slabs of cement foundation in many cases,” Mr. Doggett said.

So far, the National Weather Service confirmed at least 200 tornado touchdowns, including two colossal EF-5s, which are cyclones with wind speeds in excess of 200 mph. Mr. Doggett said April 27 marked the first time in more than 20 years that two EF-5s touched down the same day.