|Above: MODIS image of Hurricane Matthew near landfall on October 8, 2016. High wind shear of 30 knots due to strong upper-level winds from the mid-latitude jet stream was distorting the cloud pattern and weakening the storm. Matthew approached the Southeast U.S. coast as a Category 4 storm with 140 mph winds, but wind shear reduced it to a Category 1 hurricane with 75 mph winds when it came ashore about 25 miles northeast of Charleston, South Carolina. Matthew killed 49 people in the U.S. and did $11 billion in damage. Image credit: NASA.|
It’s well-known that high wind shear—a large change in the wind speed and/or direction with height in the atmosphere—is hostile for hurricane development, since a strong vertical change in winds creates a shearing force that tends to tear a storm apart. For example, even though the Caribbean is warm enough year-round to support hurricanes, we almost never see hurricanes in the winter or spring, since wind shear is very high these times of year due to strong upper-level subtropical jet stream winds.
When low wind shear occurs in summer or fall in the Atlantic’s main development region (MDR), from the coast of Africa through the Caribbean, an active period for major hurricane activity often results. But the major hurricanes that form in the MDR during these situations often have trouble maintaining their intensity when they reach the Southeast U.S. coast, since low wind shear in the MDR is typically accompanied by high wind shear along the Southeast U.S. coast. This high shear, typically associated with strong upper-level winds from the mid-latitude jet stream, helps protect the U.S. East Coast against strikes by full-strength major hurricanes.
But research published last month led by Mingfang Ting of Colombia University, Past and Future Hurricane Intensity Change along the U.S. East Coast, found that the Southeast U.S. protective barrier of high wind shear is likely to weaken in coming decades due to global warming. Using multiple climate computer models, the researchers found that global warming is likely to cause wind shear along the Southeast U.S. coast to decline significantly, mostly due to the northward migration of the mid-latitude jet stream that would accompany the expansion of the tropics (in meteorological lingo, we call this the expansion of the Hadley Cell). Since ocean temperatures will be rising globally, in coming decades hurricanes will have more heat energy to power them and lower wind shear as they approach the Southeast U.S. coast. The authors wrote, “future hurricanes may go through stronger intensification and cause more powerful destructions when moving into the coastal region.” The models also showed reductions in wind shear along the East Coast of Asia, “where one might expect that in the future typhoons would intensify more than in the historical climate and reach higher potential intensity values.”
The models showed that this reduced shear signal should start to appear as early as the 2020s or as late as 2050. Not all the news was bad in the study, though—the models also showed a strong increase in wind shear over the Caribbean, and a modest increase over the Gulf of Mexico. These increases in shear would tend to offer more hostile conditions for hurricanes, potentially offsetting the more favorable conditions for increased intensification that warmer ocean temperatures would provide.
Highly Unusual Upward Trends in Rapidly Intensifying Atlantic Hurricanes Blamed on Global Warming, our February 2019 post.
Dangerous Rapidly Intensifying Landfalling Hurricanes Like Michael and Harvey May Grow More Common, our October 2018 post.
Extreme Hurricane Rainfall Expected to Increase in a Warmer World, our June 2018 post.
Observed Slowdown in Tropical Cyclone Motion May Portend More Harvey-Like Rainstorms, our June 2018 post
Will Global Warming Make Larger Hurricanes?, our April 2018 post.
Will Global Warming Make Hurricane Forecasting More Difficult?, our January 2017 post.
Top Ten Tropical Cyclone Events of 2016 Potentially Influenced by Climate Change, our December 2016 post.
Hurricane Patricia's 215 mph Winds: A Warning Shot Across Our Bow, our 2016 post.
Katrina-Level Storm Surges Have More Than Doubled Due to Global Warming, our 2013 post.
Damaging Katrina-Level Storm Surges are Twice as Likely in Warm Years, our 2012 post.
Big Money for Hurricane Research, our October 2006 post.
Hurricane scientists Kerry Emanuel, Jim Kossin, Michael Mann and Stephan Rahmstorf wrote an excellent May 30, 2018 realclimate.org post, Does global warming make tropical cyclones stronger?