Severe weather and flooding events resulted in a multi-billion-dollar economic loss for the US in October, signalling that annual insured US losses will again exceed $US20 billion ($27.23 billion).

Aon’s latest Global Catastrophe Recap report says there were 21 named storms in the 2021 Atlantic Hurricane Season, the third-highest number of seasonal storms since 1851.

Aon Senior Catastrophe Analyst Brian Kerschner says October is typically considered a “second season” for severe weather in the US, marking a transition from summer warmth to cooler autumn temperatures.

“This year saw one of the highest tornado tallies for the month on record as it added to what is shaping up to be another year with insured losses exceeding $US20 billion,” he said.

Mr Kerschner noted Australia has also experienced notable thunderstorm activity.

“Late October storms prompted an insurance catastrophe for multiple states,” he said.

Severe storms impacted NSW and Queensland between October 18-20, with record-breaking 16cm hailstones. Thunderstorms in SA, Victoria and Tasmania between October 27-30 generated damaging hail, heavy rains, and severe winds and prompted the Insurance Council of Australia to declare an insurance catastrophe.

Total economic and insured losses were each estimated at more than $US100 million ($136.36 million).

In the US last month, a flash flood emergency near Birmingham, Alabama killed at least four people. Total economic losses were estimated at $US325 million ($443.18 million), mostly uninsured.

There was prolific heavy rainfall along the US West Coast, known as an atmospheric river, while a late-season severe weather outbreak in the US Southern Plains and Midwest generated large hail the size of tennis balls, damaging winds and tornadoes on October 10-11. Economic losses were expected to reach at least $US300 million ($409.09 million), mostly covered by insurers.

One of the strongest mid-latitude Pacific storm systems on record prompted prolific rainfall and gusty winds across parts of California, Oregon, and Washington from October 24-27. Downed trees and floodwaters led to widespread damage to property and infrastructure. Total economic and insured losses were each expected to reach well into the hundreds of millions.

In northern Oman, Cyclone Shaheen (Gulab) made landfall on October 3 as a tropical storm, killing at least 14 people. The area had no record of such a landfall dating back to at least 1890.

In Europe, Windstorm Aurore, also known as Hendrik, became the first significant event of the 2021/2022 European windstorm season. Insurers anticipate tens of thousands of claims.

In China, significant flooding in many provinces produced total economic losses of more than $US1.8 billion ($2.45 billion).

Monsoonal flooding in Thailand since late September led to more than 330,000 homes damaged or destroyed, along with large swathes of agricultural land.