Extratropical Transition (ET) of Tropical Cyclones

ET occurs when a tropical cyclone (hurricane, typhoon) interacts with a mid-latitude trough on its way to becoming a much larger (spatially) extratropical cyclone.  During ET, the storm goes through a "hybrid" phase, where it has a warm core like a tropical cyclone, as well as fronts like an extratropical cyclone.  

Impacts from re-intensifying ET cases include a very large gale- or hurricane-force wind field, pressure falls, and heavy precipitation that often causes inland flooding.  

Sandy (2012) and Irene (2011, satellite image and rainfall totals in the above image) were classic cases of ET, with Sandy the most impressive ET (938 mb at landfall!) in recent memory.  Flooding from the ET of Irene (2011) resulted in the worst natural disaster in Vermont's history! 

My primary research interests in this area are:

  • Creating an objective dynamically-based metric that defines the time of ET and the cyclone's reintensification potential

  • Understanding the relationship between ET and precipitation, specifically related to inland flooding

  • Improving operational numerical model forecasts of ET  

Our 2009 article in Monthly Weather Review on ET and precipitation distributions   

Our 2013 article in Weather and Forecasting on how the St. Lawrence River Valley modulates precipitation during ET 

                  Below are animations from 3 (in)famous cases of ET.  Sandy (top), Irene (middle), and Isabel (2003, bottom).                              The warm colors represent the mid-latitude trough while the cold colors represent the cyclone.  While Sandy and Irene featured intense interaction between the two systems, the trough in Isabel was too weak and far away from the storm, resulting in a complete heavy rainfall forecast bust in upstate New York and Ontario!  

  ET of Sandy (2012)

ET of Sandy (2012)

  ET of Irene (2011)

ET of Irene (2011)

  Non-ET of Isabel (2003)

Non-ET of Isabel (2003)