CSU hurricane forecasters predict high risk of U.S. landfalls in 2013

by Artemis on April 11, 2013

Another of the well-respected hurricane forecasters has published its predictions for the 2013 Atlantic hurricane season and, like the forecasters we covered the other day, they call for an active season with a heightened risk of landfalling hurricanes on the U.S. coastline. This forecast is from the Colorado State University Department of Atmospheric Science, led by Phillip Klotzbach and William Gray. We’ve been following their forecasts since they began working together in 2000.

They anticipate that the 2013 Atlantic basin hurricane season will see activity levels above the 1981-2010 average, noting as the other forecasters have that the Atlantic ocean surface has warmed over the last few months which can increase the potential for hurricanes to form and also enable them to intensify more rapidly and to greater strengths. The forecast also notes that the chances of an El Niño event this summer and autumn are unlikely, which could have lowered the forecast as El Niño years tend to see less severe hurricane seasons.

The forecast from CSU calls for 18 named tropical storms to form during the 2013 season, the average is 12. 9 of those storms are forecast to intensify to hurricane levels (the average being 6.5), with 4 hurricanes intensifying to major hurricane status of Category 3 or higher (the average being 2).

Klotzbach and Gray forecast an above average probability for major hurricanes making landfall on the U.S. coastline as well as in the Caribbean. For the entire U.S. coastline the forecast gives a 72% chance of a major (Category 3, 4 or 5) hurricane making landfall, while the average for the last century is 52%. For the U.S. east coast including the Florida peninsula they give a 48% chance of a major hurricane landfall, with the average being 31%. For the Gulf Coast, from the Panhandle to Brownsville, the chance of a major hurricane landfall is 47%, the average is 30%. The probability of at least one major hurricane tracking into the Caribbean is given as 61%, the average being 42%.

So, the number of storms and hurricanes forecast is for a season well above average and the probability of major hurricanes making landfall is also well above the long-term average, according to the CSU forecast. Perhaps the best metric for thinking about how risky this season is likely to be, according to the CSU forecast, is its measure of Net Tropical Cyclone (NTC) activity. It puts the NTC for the 2013 hurricane season at approximately 175% of the long-term average, significantly above the average season. It also uses the Accumulated Cyclone Energy (ACE) metric, for which the 1981-2010 average is 92 but forecasts the 2013 ACE to be 165.

So this forecast, which you can read in detail here, calls for a 2013 Atlantic hurricane season with activity and landfall levels well above the long-term averages. That is aligned with the forecasts we covered the other day here and have listed on our 2013 Atlantic Hurricane Season page.

It looks, from all the forecast data currently available, that another active hurricane season is ahead of us, but perhaps a season with a greater chance of impact to land from hurricanes if these forecasts prove correct. That makes it a season that insurers, reinsurers and catastrophe bond and ILS investors will want to watch closely, so make sure you bookmark our 2013 Atlantic Hurricane Season page.

One final set of metrics from the CSU forecast for you; on a State-by-State basis the probabilities of hurricanes making landfall are as follows (with climate averages in parentheses):

State Probability of Hurricane Impact Probability of Major Hurricane Impact
Alabama 25.7% (15.6%) 4.5% (2.6%)
Florida 71.3% (51.0%) 33.8% (21.0%)
Louisiana 46.7% (30.2%) 19.5% (11.7%)
Mississippi 17.7% (10.5%) 7.7% (4.5%)
New York 12.8% (7.5%) 5.6% (3.2%)
North Carolina 44.2% (28.3%) 12.8% (7.5%)
South Carolina 28.2% (17.3%) 6.6% (3.8%)
Texas 50.2% (32.9%) 19.5% (11.7%)

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