Lloyd's insurer Amlin estimates that its net claims from the April and May US tornadoes will be $50m.
The company has also bought an additional $40m of reinsurance cover during the second quarter.
Amlin said any deterioration in its loss estimates will be partly recoverable from its reinsurance programme. In addition, the company said the structure of its reinsurance programme for London allows for significantly increased reinsurance protection being available for future major events in 2011.
Amlin said estimated claims from the New Zealand and Japan earthquakes remain subject to uncertainty. The net reserve for these events remains materially unchanged, it added.
The rates for the US catastrophe reinsurance business underwritten by Amlin increased by 7% in the June and July renewals, the company said. It estimates that international catastrophe reinsurance rates increased by 50% over the same period.