2017 Hurricane Outlook

Tropical Storm Arlene over the north Atlantic Ocean in April 2017  (Source: NOAA)

NOAA just issued its forecast for the upcoming hurricane season that starts Thursday, June 1.  They expect 11 to 17 tropical storms, of which 5 to 9 will become hurricanes and 2 to 4 of these will intensify into “major” hurricanes.  A “major” hurricane is defined as Category 3 or higher on the Saffir-Simpson scale, with sustained winds of at least 111 mph.  

NOAA’s forecast is significant because it represents their first forecast for a potentially busier than average season since 2012.  An “average” hurricane season has 12 tropical storms, 6 hurricanes and 3 major hurricanes.  NOAA’s forecast is busier than Colorado State University’s forecast that called for only 11 tropical storms, 4 hurricanes and 2 major hurricanes.  However, CSU’s forecast was last updated before Tropical Storm Arlene developed in late April and before the latest El Nino outlook was available.  Scientists at CSU will update their forecast this week to coincide with the start of hurricane season.  Some other groups also issue seasonal hurricane forecasts but the two most famous ones are issued by NOAA and Colorado State University.

NOAA scientists said that “‘Weak or non-existent’ El Nino is a factor” in its seasonal forecast.  During an episode of El Nino, conditions in the tropical Atlantic Ocean tend to be less favorable for tropical storms and hurricanes to develop and intensify.  An El Nino event is characterized by an above normal amount of wind shear – winds that change direction with height – and near to below average sea surface temperatures in the tropical Atlantic.  

A hurricane does not have to be a “major” storm to be a damaging or deadly one.  Hurricane Isabel in 2003, Ike in 2008 and Irene in 2011 were only Category 2 storms when they made landfall, but all rank among the costliest hurricanes in the United States.  Even tropical storms and their remnants have the potential to be damaging and deadly.  For example, Tropical Storm Allison in 2001 was so destructive that its name was retired.

Whether or not the hurricane season is busier than average is also less important than if the tropical storms and hurricanes impact land areas.  There have been several busier than average hurricane seasons in the last decade, but no “major” hurricane has made landfall in the United States since Wilma in 2005.  Ironically, the 1992 hurricane season was quieter than average but was also the year of infamous Hurricane Andrew.