Stock prices will increase on the misplaced expectoration that premiums will increase. They won't.
Losses now estimated to be $20 billion. Not all of this is insured, at least not by the private industry. Last I looked, the US insurance industry has some $550 billion of surplus (its capital base), including $110 billion held by US reinsurance companies ($78 billion held by Gen Re and BH Re, so guess who has the big exposure). So do the math -- it ain't a big deal.
Berkshire paid out roughly 2 billion in claims for 9/11... but insurance premiums for the industry as a whole did increase (at least, that is how I read it). I am not sure that won't happen again in the aftermath of a storm... as more people want to be insured for the next one.