Why were there so many hurricanes this year?
This past hurricane season brought seven hurricanes, with three major hurricanes devastating the United States. Hurricane Harvey hit Texas directly and brought catastrophic amounts of rain to Houston. Next came Irma, which cleared entire islands in the Caribbean and struck into Florida after. Maria followed, but ended up taking a direct hit on Puerto Rico. According to Fortune Magazine, just Harvey and Irma alone cost about $150 billion in damage and $200 billion in lost of productivity.
According to Maggie Astor, a reporter from The New York Times, this hurricane season was abnormal. These unusually large and powerful storms were caused by climate change. According to NASA, hurricanes are “giant engines that use warm, moist air.” They only form in warm water when the “warm, moist air over the ocean” rises and causes an area of low pressure near the water surface. Then air “from surrounding areas with higher air pressure pushes in to the low pressure area.” This starts the swirling process and, gradually, the swirling system will emerge to a tropical storm and then eventually a hurricane. According to the National Hurricane Center, a normal Atlantic hurricane season usually produces around 5 named systems by mid-September. What makes this season special is that we already have 13 named systems and we are halfway in the season.
Why do we already have this many hurricanes mid-season? According to Business Insider, the “warm ocean temperatures in the Caribbean allowed this year’s storms to rapidly gain power.” The extraordinary warm temperatures of the Atlantic encourage storm formations; these warm waters constantly feed the newly-formed tropical storms, turning them from tropical storm status to major hurricane status.
Along with an increase in sea temperatures, we are also experiencing a “lack of El Niño” conditions this year. According to the National Oceanic and Atmospheric Administration, El Niño is the warm “phase of a recurring climate pattern across the tropical Pacific.” Whenever an El Niño occurs, the tropical Pacific experiences an increase in sea surface temperatures. La Niña is the opposite of El Niño. During La Niña, the tropical Pacific holds lower sea surface temperatures than average.
Why do ocean temperatures out in the Pacific matter to the Atlantic hurricane season? It all comes down to La Niña’s effect on the atmosphere. The National Oceanic and Atmospheric Administration states that the upper atmosphere “is associated with weaker upper- and lower- level winds, both of which reduce the vertical wind shear and increase hurricane activity.” This in turn causes the atmosphere to be less stable and provides favorable hurricane formation.
Overall, two factors played a key role in this abnormal hurricane season: the rare temperatures of the Atlantic and La Niña. Each factor alone could already create a very active hurricane season. However, with both conditions active this season, we are experiencing a one of a kind hurricane season that is bringing astronomical damage to the Caribbean and Florida.