"Alberto" and the start of the 2018 Atlantic Hurricane Season

NOAA's Projected Track for "Alberto"  (Source: National Hurricane Center)

The 2018 Atlantic hurricane season has gotten another head start with a named storm prior to the June 1 start of the season for the fourth time in the past six years.  The National Hurricane Center determined that “Alberto” developed into a subtropical storm on May 25 near the Yucatan Peninsula.  The National Hurricane Center has recognized “subtropical storms” since 1972 and they have characteristics of both a tropical and extratropical storm.

Alberto is impacting parts of the U.S. Gulf Coast and the state of Florida with heavy rain and gusty winds along with some coastal flooding and isolated severe weather.  The National Hurricane Center doesn't expect Alberto to reach hurricane strength before it makes landfall tomorrow.  That means heavy rain and the potential for flooding will likely be the greatest dangers associated with Alberto.  

NOAA recently issued its seasonal outlook for the 2018 Atlantic hurricane season.  It calls for 10 to 16 tropical storms, of which 5 to 9 become hurricanes with 1 to 4 of those becoming major hurricanes.  A tropical cyclone becomes a tropical storm when sustained winds around the center reach 39 mph, while a tropical storm is upgraded to hurricane status when sustained winds reach at least 74 mph.  A hurricane is considered “major” when it reaches Category 3 status on the Saffir-Simpson Scale with sustained winds of at least 111 mph. 

The private weather forecasting company, AccuWeather, released a similar Atlantic hurricane forecast last month for 12 to 15 tropical storms, 6 to 8 hurricanes with 3 to 5 becoming major hurricanes expected in 2018.  Colorado State University (CSU) scientists also released a seasonal hurricane forecast last month that called for 14 tropical storms in the Atlantic Ocean, with 7 hurricanes and 3 major hurricanes.  CSU will update its forecast this week.  

An average Atlantic hurricane season has 12 tropical storms, 6 hurricanes and 3 major hurricanes.  By comparison, the record-setting 2017 Atlantic Basin hurricane season (that includes the Caribbean Sea and Gulf of Mexico) saw 17 tropical storms of which 10 became hurricanes.  Six of the 10 hurricanes that developed last season intensified into major hurricanes. According to the National Hurricane Center, last season saw the highest number of Atlantic tropical storms since 2012, as well as the most major hurricanes since 2005.  

NOAA is watching the possibility of a weak episode of El Nino developing during the hurricane season (June 1 – November 30) and, therefore, doesn’t expect this season to be as busy as last year.  El Nino refers to the periodic warming of the tropical east Pacific Ocean.  That helps create less favorable conditions for tropical storm formation in the tropical Atlantic, namely an increased amount of wind shear and slightly cooler sea surface temperatures.  Tropical storms and hurricanes rely on warm ocean water (commonly at least 80° Fahrenheit to a depth of at least 200’) as a fuel source.

People should remember that the overall number of tropical storms and hurricanes is less important than where they track.  The Atlantic Ocean can have a very active hurricane season like in 2010 when a total of 19 tropical storms including 12 hurricanes developed, but none had significant impacts in the United States.  Meanwhile, a quiet hurricane season, like in 1992 had just one major hurricane.  However, Hurricane Andrew remains only the third and most recent Category 5 hurricane to make landfall in the United States.