The Atlantic hurricane season officially starts today, June 1, and goes until November 30. The Eastern Pacific season started on May 15, and also goes to November 30. We had our first Pacific storm just the other day: tropical storm Agatha hit Guatemala.
Since at least 1994, the Tropical Meteorology Project at Colorado State University has issued predictions on the upcoming Atlantic hurricane season. They issue three predictions each year:
- In December, they publish their predictions for the upcoming season.
- In April, they publish an updated prediction for the season that will start on June 1.
- In August, they publish yet another update.
You might wonder why they publish an update in the middle of the season. The answer can be found in their FAQ:
Although the Atlantic basin hurricane season starts on June 1, more than 90 percent of all tropical cyclone activity and 95 percent of major hurricane activity occurs after August 1 in an average season. In general, our seasonal forecasts issued on August 1 show the greatest skill.
The TMP also publishes an annual report that summarizes the most recent hurricane season and compares their predictions with the actual activity. Their forecasts page has links to the most recent forecasts, and a way to select previous forecasts.
Whereas the forecasts make for interesting reading, I was especially impressed with the summaries. The authors are very up front about how they derive the numbers for their forecasts, and the summaries accurately present their successes and their failures. Everything is out in the open. They don’t appear to be pushing a particular agenda, but rather reporting the results of their observations and using the observed data to try to understand and predict future behavior. This is what I was taught science is about.
One thing I’ve wondered for the past several years is what caused the recent increase in tropical cyclone activity. That there has been an increase is no secret, as I pointed out last year in Tracking Hurricanes. A common cry is, “Global warming is causing more hurricanes.” TMP’s 2009 Summary addresses that, starting on page 39. The entire section is well worth reading. A few quotes are particularly relevant:
Despite the global warming of the sea surface that has taken place between the mid 1970s to late 1990s and the general warming of the last century, the global numbers of hurricanes and their intensity have not shown increases in recent years except for the Atlantic since 1995 (Klotzbach 2006).
Although global surface temperatures have increased over the last century and over the last 30 years, there is no reliable data available to indicate increased hurricane frequency or intensity in any of the globe’s other tropical cyclone basins.
In other words, if an increase in sea surface temperature caused an increase in hurricane activity, one would expect the increased activity everywhere, not just in the Atlantic.
So, what’s the cause?
This large increase in Atlantic major hurricanes is primarily a result of the multi-decadal increase in the Atlantic Ocean thermohaline circulation (THC) that is not directly related to global sea surface temperatures or CO2 increases. Changes in ocean salinity are believed to be the driving mechanism.
Interesting. Changes in the salt content of the water, which is a localized phenomenon.
The report then gives a detailed counter to the global warming argument, showing that in two recent 25-year periods (1945-1969, during a weak cooling trend; and 1970-1994, a general warming trend), the warmer period had only 48% as many hurricanes as the cooler period. Looked at in isolation, you would conclude that cooler temperatures caused more hurricanes. That’s obviously not the case, though, when you look at all the data. So you have to conclude that the increase in hurricane activity is due to something else.
If you haven’t yet caught on, I’m impressed with the way the TMP presents their research. I encourage you to give it a look.