El Nino’s Influence on Hurricanes

Hurricane Patricia on October 23, 2015  (Source: NASA)

Today marks the final day of hurricane season in the eastern Pacific Ocean.  Unlike the Atlantic hurricane season which runs from June 1 through November 30, hurricane season in the Eastern Pacific lasts from May 15 through November 15.  According to the National Hurricane Center, the Eastern Pacific averages approximately 15 tropical storms, 8 hurricanes and 4 major hurricanes (Category 3 or higher). 

But this year one of the strongest El Nino’s on record developed in the eastern Pacific Ocean and caused a commensurate uptick in tropical activity.  During an El Nino event, the waters of the equatorial Pacific Ocean are warmer than average.  That helps create a more favorable environment for the development of tropical storms and hurricanes.  This season had a total of 16 tropical storms, 12 hurricanes and 9 major hurricanes in the tropical East Pacific.

This season also saw the strongest hurricane on record in the Western Hemisphere.  Hurricane Patricia was also the strongest ever observed in the Eastern Pacific Ocean with sustained winds of 215 mph and a minimum central air pressure of 872 millibars.  To read more specifics about how strong Patricia was and the slew of records it broke, check out my October 24 column.  Fortunately, Patricia didn’t cause as much damage as it could have since it was a relatively compact storm and made landfall in a sparsely populated part of western Mexico.

Above average tropical activity in the eastern Pacific (off the west coast of Mexico) is fairly typical during moderate to strong El Nino events.  During moderate to strong El Nino events when there’s an increased number of tropical storms and hurricanes in the Eastern Pacific, there is a corresponding decline in the number of named storms in the tropical Atlantic Ocean.  That’s because El Nino tends to contribute to unfavorable environmental conditions for tropical storms and hurricanes in the Atlantic Ocean.  Such as been the case during the quieter than average 2015 Atlantic hurricane season. 

While the presence of El Nino often indicates a higher than average chance of above average tropical activity in the eastern Pacific, it isn’t always the case.  There was no El Nino during the 2014 season, yet there was above average activity in the eastern Pacific.  Last year saw 20 tropical storms, 15 hurricanes and 8 major hurricanes.  Fortunately, there are no active tropical storms or hurricanes in the eastern Pacific or Atlantic Oceans.