$500 billion hurricane strike?

Yesterday's Houston Chronicle spoke at length about Hurricane Katrina, detailing how in studies that its devastation was not unrivaled. In it, they state that, "a $500 billion storm in a major metropolitan area along the U.S. coast, such as Miami or possibly even Houston, is conceivable by 2020.

The idea that a $500 billion hurricane hit is "conceivable" is the next 13 years is ridiculous. Katrina was an event that is expected about once every 250 years. A $275 billion dollar event is one which is expected about every 1,000 years. A $500 billion hurricane hit is so unlikely that the data doesn't go that far. The chance of a $275 billion dollar hurricane occurring in the next 13 years is about 1.3%. Remember, these are exponential numbers so as the dollar value increases, the amount the chance is lessening increases - so, a $50 billion event is not 1/2 as likely as a $25 billion event, but rather 35% as likely as a $25 billion event. What does that mean?

It means that the chance that a $500 billion hurricane hitting by 2020 is just above nil.

Is "just above nil" really the same as "conceivable"?