Dr. Bill Gray is a noted hurricane researcher who regularly issues predictions for tropical cyclone activity. He and his protégé Dr. Philip Klotzbach study global weather patterns and historical hurricane records and then issue warnings about how busy they think hurricane season is going to be. On April 6, they issued their predictions for the 2011 season, and until the season is over, they will continue to study the shifting weather patterns and issue updated reports.
THE MEAT OF IT
For the 2011 Atlantic hurricane season, Drs. Gray and Klotzbach anticipate above-average activity, with 16 named storms and five of those, major hurricanes (category 3 and above). They have calculated a 72% probability of a U.S. landfall.
The complete report, which is filled with charts, graphs and colorful maps, is available online.
I found it interesting that the researchers compared the 55-year period of 1901-1955 to 1956-2010, and the earlier period had a much higher number of named storms, hurricanes and major hurricanes. Of course, the data-gathering tools available in the first half of the 20th century was very different from what's available now.
The report also stated that we can expect busier hurricane seasons for the next ten years or so, but then it should quiet down.
HOW ACCURATE ARE THEY?
For the 2010 Atlantic hurricane season, Drs. Klotzbach and Gray issued an initial forecast in December 2009, plus three updates based on changing weather conditions. The final column is the actual number for the 2010 season. I've copied the chart below, and you can read the full report, which includes a glossary defining all the terms they use in the chart.
Another great site for historical data is provided by Unisys. Pick a year, and you can look at maps and detailed information about all the tropical activity from tropical depressions to major hurricanes.