Tropical Storm Risk’s 2011 Atlantic Hurricane Season Outlook

May 25, 2011

With the usual caveats that an active season doesn’t necessarily mean your coastal locale will be hit by a hurricane (and vice versa) and that these predictions are research projects in progress.

In my previous post, I mistakenly stated that the “next forecast to be released that I use in my forecast comparisons” would come from the Colorado State group.  That is because last year’s “pre-season forecast” from the Tropical Storm Risk consortium was more of an executive summary of their forecast than a complete package.  That was not the case this year.

Tropical Storm Risk’s forecast for 2011, joins NOAA’s and North Carolina State’s in anticipating an above average level of activity.  The group predicts fourteen tropical storms, eight hurricanes, and four major hurricanes to form in the Atlantic during the forthcoming season totaling an Accumulated Cyclone Energy of 124.**

TSR uses two predicted values to make their forecast.  One is the magnitude of east-west trade winds over the Caribbean Sea and Tropical North Atlantic in July, August, and September. .  This serves  as proxy for wind shear.  The anticipated lower than normal  wind speed is expected to have an enhancing effect on tropical storm formation.  The second predictor is forecast sea surface temperatures in the Mean Development Region (deep tropical Atlantic between Africa and the Caribbean islands).   Temperatures are expected to only be very slightly above normal; not enough to have an enhancing effect.

The consortium also tries to predict the number of storms to make landfall in the United States. They call for two hurricanes and four tropical storms to do so. I think this is merely a matter of climatological norms being adjusted upward in accordance with the forecast of increased activity overall. (The August forecast on the other hand is slightly more involved and utilizes a predicted atmospheric value).

On the basis of named storms, Tropical Storm Risks have not differed from the consensus significantly, in recent years.  Therefore, their failures and successes were usually shared by the other forecasters as well.  They have had a couple of ACE forecasts that broke from the consensus somewhat (2006 and 2009, by 16% and 9%, respectively) and in both instances, they were on the correct side by being lower than the average of the rest.  As such, their forecasts are a small bit better than the others on average, although they have not had a stand-out performance in any year.

Season TSR Named Storms/Hurricanes/Majors Hurricane Forecasts Actual TSR Accumulated Cyclone Energy Forecast Actual
2005 14/8/4 28/15/7 159 248
2006 14/8/3 10/5/2 138 79
2007 16/9/4 15/6/2 156 72
2008 14/8/3 16/8/5 131 145
2009 11/5/2 9/3/2 69 51
2010 18/10/4 19/11/5 182 166

The aforementioned Colorado State forecast will be released the day hurricane season begins, June 1.  Florida State’s should be out shortly thereafter.

**Storm numbers are rounded up/down to the nearest whole number as appropriate.


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