A New Hurricane Season

A quiet first day of the hurricane season  (Source: NOAA)

Today is the first day of the hurricane season in the eastern Pacific Ocean.  Hurricane season runs in the tropical east Pacific (north of the equator, west of Mexico and east of Hawaii) from May 15 – November 30.  The last two seasons have had several damaging hurricanes, as well as the strongest observed hurricane in the western Hemisphere – Patricia – that occurred last October. 

Mexico’s national weather organization, the Servicio Meteorológico Nacional, is calling for a near average hurricane season with 17 tropical storms, of which 9 become hurricanes and 4 of those become major hurricanes.  By comparison, an “average” season in the tropical east Pacific includes 15 tropical storms, 8 hurricanes and 4 major hurricanes.  That’s based on the running 30-year average from 1980 to 2010.  A tropical storm features sustained winds of at least 39 mph around the center of circulation.  It becomes a hurricane when sustained winds reach 74 mph.  A hurricane becomes “major” when sustained winds reach at least 111 mph – making it a Category 3 storm on the Saffir-Simpson Scale.

One of the hallmarks of a powerful El Nino event is warmer than average water in the tropical eastern Pacific Ocean.  That helps create more favorable conditions for tropical storm development.  However, there have been active seasons in the eastern Pacific Ocean during non-El Nino seasons too.  Such was the case during the 2014 season that saw 20 tropical storms, 15 hurricanes and 8 major hurricanes.  Although no tropical storms have developed yet in the eastern Pacific in 2016, there has been at least one named storm during the month of May every year since 2011.

Having a moderate to strong El Nino or La Nina doesn’t always correlate to an above or below average hurricane season in the eastern Pacific or Atlantic Ocean.  For example, the 2013 and 2014 hurricane seasons were both quieter than average in the Atlantic Ocean, while the tropical east Pacific had more named storms than average each year.  Although the presence of El Nino or La Nina can influence the tropics, a number of factors play a role in how active the tropics become (e.g. amount of wind shear, sea surface temperatures).  Hurricanes require a lack of wind shear as well as warm sea surface temperatures of at least 80 degrees Fahrenheit to develop.

While the tropical east Pacific has been busier than average since 2013, the tropical Atlantic hasn’t had an active hurricane season since 2012.  However, having fewer storms doesn’t mean you should be any less prepared.  Many significant storms have occurred in quieter than average seasons, such as Andrew in 1992.  Now that hurricane season is underway in the tropical east Pacific, NOAA will watch for any tropical development and will issue its forecast for the 2016 Atlantic hurricane season before it begins on June 1.