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.

Significant November Hurricanes

Hurricane Paloma in November 2008 (Source: NASA)

When Hurricane Kate developed this week, it became the first November hurricane in the Atlantic Ocean since Tomas in 2010.  Fortunately, Kate didn’t have much of an impact on any land masses and was a relatively short-lived storm as is typical in November.  Although November normally features little, if any, activity in the tropics, some noteworthy hurricanes do form on occasion.

 

2009: Hurricane Ida was a significant late season Category 2 storm.  Ida was also the strongest Atlantic hurricane to make landfall during the 2009 season when it struck the Nicaraguan coast as a Category 1 storm.  However, Ida weakened to a tropical storm and started to lose its tropical identity when it made landfall on the U.S. Gulf Coast –where it brought appreciable rainfall and gusty winds.  Mid-Atlantic residents also felt its indirect impact as Ida’s remnants served as a catalyst for an early-season Nor’Easter.  It brought gusty winds and a cold rain up and down the East Coast.

2008: Hurricane Paloma formed in the southwest Caribbean Sea, which is an area favorable area for tropical storms and hurricanes late in the season.  Paloma reached its peak intensity on November 8 as an intense Category 4 hurricane with sustained winds of 145 mph and a minimum central air pressure of 944 millibars.  The lower the air pressure, the stronger the storm is.  By comparison, standard sea level air pressure is approximately 1013 millibars.  Paloma was the strongest Atlantic hurricane to form in November since Michelle in 2001.  Paloma was also significant because it marked the first known instance where major hurricanes formed in the Atlantic Ocean Basin in five consecutive months (July through November). 

2001:  Although November rarely sees major hurricanes, that wasn’t the case in 2001.  According to the National Hurricane Center, Michelle became a Category 4 hurricane on November 3 with sustained winds of 140 mph and a minimum air pressure of 933 millibars.  Hurricane Michelle caused major damage and claimed more than 20 lives across the Caribbean during its destructive lifespan.

1932: The strongest November hurricane on record occurred so long ago that it developed before hurricanes were named and is referred to as the “1932 Cuba hurricane.”  This was November’s only Category 5 hurricane on record to develop in the Atlantic Ocean.  On November 6, 1932 the hurricane reached its peak intensity with maximum sustained winds of approximately 175 mph and a minimum central air pressure of 915 millibars.  Since hurricane hunter flights didn’t begin until the early 1940s, the most accurate way to measure the intensity of an offshore tropical storm or hurricane were ships at sea.  These measurements weren’t made at the center of the storm so the air pressure could have been even lower.

Fortunately, none of these hurricanes had a direct impact on the United States.  The last tropical system to have a significant impact in the United States during the month of November was Gordon in 1994.

Weather Quiz

Lenny was a rare November Category 4 hurricane (Source: NOAA)

Before Kate, when was the last time a tropical storm developed in the Atlantic Ocean during the month of November?

A.  1999

B.  2008

C.  2010

D.  2013

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Answer to Weather Quiz question from October 31.

True.  The only two Halloweens during the last 22 years that had measureable rainfall in the Nation’s Capital were in 2002 and 2009.