Looking Ahead to Hurricane Season

 

Hurricane Iota, November 2020 (Source: Tropical Tidbits)

While the 2021 Atlantic hurricane season doesn't officially get underway until June 1, researchers at Colorado State University recently released their April outlook for the upcoming season.  They're expecting another active one with 17 tropical storms, of which 8 become hurricanes, including 4 major ones.  By comparison, the 2020 Atlantic hurricane season produced 30 tropical storms with 13 hurricanes, and 6 of them major. 

NOAA’s 30-year average for the Atlantic hurricane season is updated every decade.  Starting this season the average has been updated to reflect the 30-year period of 1991 – 2020.  Therefore, an “average” Atlantic hurricane season now has 14 tropical storms, 7 hurricanes, 3, of which, become major.  A “major” hurricane is a Category 3/+ on the Saffir-Simpson Hurricane Wind Scale and has sustained winds of at least 111 mph.

The fact NOAA increased its average numbers for an Atlantic hurricane season shouldn’t come as a surprise considering how active the tropical Atlantic has been over the last decade.  Another key factor to consider is how at least one named tropical storm has developed prior to the official start of the hurricane season every year since 2015.  That’s why it’s important not to be lulled into a false sense of security, especially if you live on or near the coast, as tropical storms and hurricanes do sometimes develop prior to the official start of the season.

One of the key facets in CSU’s hurricane forecast for 2021 is the status of ENSO or the “El Nino Southern Oscillation.”  That’s basically whether or not there’s a La Nina or El Nino present.  An episode of La Nina is characterized by below average sea surface temperatures in the equatorial Pacific Ocean, off the west coast of Mexico and Central America.  When that happens there is often a commensurate rise in sea surface temperatures in the tropical Atlantic along with a decrease in the amount of wind shear.  Both events are conducive to tropical development in the Atlantic.  The opposite is true during an episode of El Nino when the tropical Atlantic is normally quieter.  ENSO-neutral conditions, the absence of La Nina or El Nino, also favor above average activity in the tropical Atlantic.

There are other facets that go into the seasonal hurricane outlook that I will describe in a future column, but the presence of El Nino or La Nina is of paramount importance in issuing such a forecast.  It’s also possible for there to be neither phenomena present and that’s referred to as “ENSO neutral” conditions.  The first named Atlantic storm of the 2021 season will be “Ana.”