Wrap-Up of 2006-2007 Southern Hemisphere Tropical Cyclone Activity

Well, it's April 30, which means that for most of the Southern Hemisphere, hurricane season just ended. It hasn't been a particularly busy year for any of the Southern Hemisphere cyclone regions except the Southwest Indian Ocean, which took one hell of a beating (see above; image courtesy of Meteo France).

Let's look at the two other relevant regions first. Different divisions are possible, but Wikipedia breaks them into the Australian region and the South Pacific. During the 2006-2007 season, each of these areas saw relatively little activity, save for one kickass storm apiece. For the Australian region that storm was Cyclone George (officially at Category 3 although I suspect it may have been stronger); for the South Pacific, it's Category 4 Cyclone Xavier.

But one strong storm hardly makes for a very busy year in either of these regions. If you compare what we saw in 2007 to South Pacific activity in 2005--when four Category 4 or 5 storms occurred in the short space of about a month--it's clear this year was far quieter. Similarly, if you compare 2007 to Australian region activity in 2006--when a very large number of intense storms were also seen, including two Category 5s--it was, again, a quiet year this year.

When I was in Melbourne recently, I got to hear the chief scientist at the Australian Bureau of Meteorology, Dr. Neville Smith, give a breakfast presentation about the agency's work. When I stood up at the end and asked about the 2007 cyclone season and why it had been so inactive in the region, Dr. Smith noted that that's what's expected during El Nino years, like the one we just had. But my understanding is that even for El Nino conditions, it was really pretty quiet for cyclones down under this year. (Granted, the people who got slammed by Cyclone George in Port Hedland might beg to differ.)

But of course, for the Southern Hemisphere, the people who got it worst this year from tropical cyclones were the Malagasies (or is it "Madagascans"?). Madagascar is in a state of crisis because it was directly struck or otherwise affected by no less than six storms during the 2006-2007 season, including a number of very powerful ones. That goes to show you just how active it was in the Southwest Indian basin: There were 4 Category 4s (Bondo, Dora, Favio, and Indlala) and 2 Cateory 3s (Gamede and Jaya, although again, I suspect Jaya could have been stronger).

All of which now allows us to summarize intense storm activity for the entire Southern Hemisphere in 2006-2007. First of all, unlike during the previous two seasons, there wasn't a single Category 5 storm. Moving down the intensity scale, there were 5 total Category 4s, and 3 total Category 3s. In my view, two of those Category 3s may also have been Category 4s, but in any event, they are not officially so designated at this point. (In this context it's rather fitting that an article in the latest issue of the Bulletin of the American Meteorological Society suggests scrapping the familiar Saffir-Simpson scale and replacing it with a scale more sensitive to storm size variations and their considerable implications.)

Over all, one can only conclude that except in the Southwest Indian region, 2007 was on the quiet side for the Southern Hemisphere as a whole. To be sure, one shouldn't draw any overly ambitious conclusions about this fact, any more than one should draw overarching conclusions on the basis of the relatively quiet 2006 Atlantic hurricane season. There's huge natural variability within and between hurricane basins. Any basin in any year can do pretty much anything.

So now things shift to the far more active Northern Hemisphere, which typically sees twice as much total tropical cyclone activity as the Southern. It will be interesting to see whether our hemisphere, over all, compensates in 2007 for the somewhat quiet season south of the equator. I'll be following this question closely. We'll begin to get more of a sense of what to expect starting May 4, when the next of the forecasts for the Atlantic in 2007 comes out....