Today is officially the last day of the 2007 Atlantic hurricane season. Not that we can’t have a storm after November 30…but it becomes less and less likely.
And how do we summarize the year? Well, less active than expected, especially when it comes to the frequency of the most intense storms. That’s two years in a row the forecasts have overshot in this respect.
Anyways, over at the Daily Green I now have a more in-depth post-mortem on the season. Some highlights:
The relative quietude of the 2007 Atlantic hurricane season seems particularly mystifying in light of the fact that we saw La Nina conditions develop in the tropical Pacific — which usually correlate with above average Atlantic storm activity. So lets turn to Klotzbach and Gray to hear their reasons for why we had a quiet year. Notably, sea surface temperatures were 0.2 to 0.5 degrees (Celsius) cooler than the average of the past twelve years — a development that Klotzbach and Gray ascribe to high levels of African dust blown across the ocean, which deflected sunlight. Meanwhile, although La Nina tends to reduce storm-killing vertical wind shear over the Atlantic, this time around it really didn’t.
Meanwhile, the month of September was just plain quirky: No less than eight storms formed, but because some were close to land and others just happened to encounter other unfavorable conditions, none developed past short-lived Category 1 hurricane status.
But even on top of all this, October remains the deepest mystery. Or as Klotzbach and Gray put it: “We are still struggling to understand why October was not more active.” All the conditions were favorable. But very little happened. It’s still not really clear why.
The upshot from all of this: We still have a great deal to learn when it comes to forecasting seasonal hurricane activity in advance. Nevertheless, all forecasters agree that whatever may happen in a given year, we remain in an active hurricane era in general. And even though the United States has now enjoyed a welcome respite for two straight years, there’s no reason to expect easy times to continue.
You can read the full item here.