US emergency services and UK insurers are preparing for the worst this week as the biggest tropical storm in four years closed in on Washington DC.

The strength and direction of Hurricane Isabel make it the most dangerous storm to threaten the US mainland since Hurricane Floyd in 1999 and the worst to approach Washington DC since Hazel in 1954. The 120mph winds and storm force waves were predicted to hit North Carolina sometime this evening. The hurricane was then expected to move north toward Washington DC.

The alarm was sounded along the US East Coast on Tuesday morning, prompting syndicates at Lloyd's to check their exposure in the danger zone. Teams of loss adjusters from companies such Crawford & Co and Benfield prepared to fly out to the potential disaster area.

Just weeks after Hurricane Fabian caused $1bn of damage in Bermuda, Isabel could bring with her a bill three times the size. Hurricane Floyd cost the industry $2.5bn in 1999.