Hurricane Trends

Category 1 Hurricane Irene nearing landfall in NC on 8/27/2011  (Source: NOAA)

From now until early October is climatologically the most active part of the Atlantic hurricane season, which runs through the end of November.  This season has already seen seven named tropical storms and three hurricanes, but no major ones.  The National Hurricane Center has been monitoring a tropical wave the last few days as it heads through the Bahamas, but it hasn’t developed into a tropical storm.

Scientists with NOAA and Colorado State University recently updated their seasonal forecast for the remainder of the 2016 Atlantic hurricane season with the expectation for an average to slightly busier than average season.  An “average” season sees approximately 10 tropical storms, six hurricanes and two major hurricanes, so there are still a few storms to go to meet that criteria.  That’s shouldn’t be a problem, though, as we enter what is typically the most active portion of the hurricane season.

The Atlantic Ocean has seen an uptick in tropical storm and hurricane development since 1995.  While the last few seasons have seen a near average number of tropical storms and hurricanes, there has been a significantly higher than average number of storms over the last two decades.  From 1995 through 2015, there was an average of approximately 15.4 tropical storms, 7.4 hurricanes and 3.5 “major” hurricanes (Category 3 or higher on the Saffir-Simpson hurricane scale with sustained winds at/above 111 mph).  During the same twenty-year span, there were nine Category 5 hurricanes – as strong as hurricanes get.

Several damaging and deadly hurricanes have impacted the United States since 2005 – including Ike in 2008, Irene in 2011 and Sandy in 2012 (which was officially declared a “post-tropical” system when it made landfall in the United States).  However, none of these were major hurricanes.  The fact that Ike, Irene and Sandy all rank among the costliest natural disasters in U.S. history illustrates that a hurricane doesn’t have to be “major” to have significant impacts.  A tropical system doesn’t even have to be a hurricane to be damaging.  For example, Tropical Storm Allison made landfall in Texas and caused record flooding across much of the U.S. Gulf Coast in 2001.  Allison was the first of only two tropical storms to have its name retired by the World Meteorological Organization for being especially damaging or deadly. 

Although a number of catastrophic storms have developed during the last 20 years, there has been a noticeable downturn in the number of significant tropical storms and hurricanes that have impacted the United States in recent years.  This can be partly attributed to simple luck that storms haven’t made landfall in the United States as frequently in the last decade as they did through 2005.  Scientists also point to global weather events such as an episode of El Nino or La Nina which can lead to an above or below average hurricane season.  The next tropical storm that develops in the Atlantic Ocean will be named “Hermine.”