Looking Ahead to Hurricane Season

Ocean City, Maryland (Photo Credit: Ashley Adams)

Although hurricane season doesn’t officially get underway until June 1, this is a good time to discuss the upcoming season.  That’s because at least one tropical storm has developed in the Atlantic Ocean Basin prior to June 1 in six of the last eight years.  A respected group of scientists with Colorado State University (CSU) recently issued its April outlook for the 2020 hurricane season.

Researchers at CSU have been issuing seasonal hurricane forecasts since the 1980s and they’re known for being remarkably accurate.  Citing an absence of El Nino conditions and warmer than average sea surface temperatures in parts of the tropical Atlantic (along with several other factors), a busier than average hurricane season is expected.  CSU predicts 16 tropical storms of which 8 become hurricanes, with 4 of those becoming “major” hurricanes.  An “average” Atlantic hurricane season has 12 tropical storms with 6 hurricanes and 2 or 3 major hurricanes.  That’s based on statistics from 1981 through 2010.

A system becomes a tropical storm and receives a name when sustained winds around the center of the storm reach 39 mph.  When sustained winds reach 74 mph, then the tropical storm is officially upgraded to hurricane status.  A hurricane becomes major when sustained winds reach at least 111 mph, making it a Category 3 on the Saffir-Simpson Hurricane Wind Scale. 

The last four hurricane seasons have been busier than average with a total of six Category 5 hurricanes since 2016.  That’s the highest such total since eight developed from 2003 – 2007.  Category 5 hurricanes occur in the rarest of circumstances and have sustained winds of 156/+ mph.  Hurricane Michael (2018) became only the fourth Category 5 hurricane to make landfall in the United States.

Hurricanes don’t have to be “major” to have significant impacts.  Hurricane Florence made landfall as a Category 1 hurricane in North Carolina but proceeded to cause devastating flooding well-inland.  There have also been quieter than average seasons with catastrophic storms, such as Andrew in 1992.  Hurricane Andrew was the only major hurricane of the 1992 season but was the third and last Category 5 hurricane to make landfall in the United States prior to Michael two years ago.

Some factors meteorologists consider when issuing seasonal outlooks for hurricane season include the presence of El Nino or LaNina.  The El Nino Southern Oscillation (ENSO) has three phases: El Nino, La Nina, or neutral meaning the presence of neither.  El Nino conditions are characterized by below average Atlantic sea surface temperatures (SSTs) and above average wind shear (differing wind speeds with altitude) in the tropical Atlantic.  Both of these serve to inhibit tropical development.  La Nina is the reverse with warmer than average Atlantic SSTs and little to no wind shear.

During years with a weak El Nino, La Nina, or ENSO neutral conditions, the Atlantic could see average to above average tropical activity.  That’s the case now with ENSO neutral conditions present and expected to continue this spring and summer.  Although NOAA won’t release its seasonal outlook for the 2020 Atlantic hurricane season until late May, it should be similar to that of Colorado State University’s forecast for an above average 2020 season.