uh, sure, except these aren't independent trials. to clarify, the event of being in a storm now, and the event of being in a storm one minute from now are almost perfectly correlated. this means you can't use the product rule.
by contrast, the event of a storm happening this year vs. a storm happening next year are closer to independent exactly because the blocks are bigger (a storm on Dec. 31 will make a storm on Jan. 1 more likely, but apart from that...).
your 'improvement' rests on assumptions which are not only unwarranted, but obviously untrue.