It's nearly June, and the 2006 hurricane season (for those of of us in the eastern US) is upon us. I thought I'd take a look at the historical trends for hurricanes, and there's a lot of data out there. This site has a nifty table of frequencies (up to and including 2004) - and it illustrates something interestesting: notice how frequency had a local peak in the 1941-1950 interval, and then started to drop? That coincides with the end of WWII, and the rise in prosperity in the US. It also coincides with the spread of inexpensive air conditioning.

What does that mean? It means that people started to move south in large numbers. In particular, coastal development ramped up - along both the US east coast and along the gulf coast. It almost certainly seemed safer - the table tells the story. According to that data, the annual hurricane frequency has been below average since about 1950.

Mind you, the data only goes back to 1851, and that's a very short time in climate terms - the "average" for such a short time span could well be meaningless. In behavioral terms though, it's not. The building boom along the coasts coincided with a period of lower activity, and people didn't remember that really bad storms (1935, for instance) were not just possible, but highly probable. We tend to completely ignore things that we don't have personal experience with.

So, have a look here; while there were two absolutely awful hurricanes last year, the raw numbers were 15 storms of category 1 or higher (storms get names if they hit tropical level - category one is much stringer). In 2005, 15 storms hit category 1 or higher. And out of that 15, you have to drop the ones that never got to the US mainland in order to fithem into that table. That data is further down in the second tabll, and it was 5 storms. So from 2001-2005, that gives us 14 storms that got to level one or above, and also hit the US mainland.

Which means that we are back into the kind of active period that we last saw (again, here in the US) back in the 1940s - before the current buildup on the coasts happened. What does all that mean? Darned if I know - in looking at the data since 1851, it looks like we've been in a relatively quiet period since 1950. As I said above though, this is such a short interval in climate terms that it may be meaningless. The only real conclusion I can come to is this: it was probably a mistake to build as much as we have near the coasts. I'm guessing that insurance rates will reflect that pretty quick.

If you want to track these storms yourself (I do, since my parents live on the east coast of Florida), then you should subscribe to the NOAA tropical storm feed.