As illustrated in the figure below, the historical proportion between basin counts and landfalls has been very volatile on an annual basis. There is only a weak correlation between hurricane counts in the Atlantic Basin and the number of U.S. landfalls. The statistical significance is a subject of some debate in the scientific community. (1)
The year to year volatility warrants preparation for any season. The quiet 1992 season saw only four hurricanes with one making a very impactful and historic U.S. landfall. Meanwhile, the 2010 season saw 19 named storms and 12 hurricanes, without a single U.S. landfall. In 1985 there were seven hurricanes in the basin, and six of these made U.S. landfall (some of which were very impactful).
Seasonal activity predictions for the basin are valuable, but the impacts of even a single tropical storm or hurricane landfall (quiet season or not) can be quite severe. Historical experience warrants proper review and preparation of hurricane plans by all interests from individual homeowners to businesses to the (re)insurance industry at large.
In light of this reality, seasonal outlook providers expect 2015 basin counts to fall below the long-term mean of 1955-2014. The expected counts also fall clearly below the short-term 1995-2014 mean, reflecting the current warm phase of the Atlantic Multidecadal Oscillation.
Factors of greatest influence include:
1. A moderate El Niño expected through the 2015 hurricane season.
2. Cooler than normal Sea-Surface Temperatures (SSTs) in the Atlantic Main Development Region (AMDR).
The predictions of seasonal outlook providers, including the Colorado State University team of Professors William A. Gray and Phillip J. Klotzbach, are included in the table below.
1. Coughlin, K., Bellone, E., Laepple, T., Jewson, S., Nzerem, K., 2009: A relationship between all Atlantic hurricanes and those that make landfall in the U.S.A. Quarterly Journal of the Royal Meteorological Society, 135, 371-379.