Impacts of Extratropical Forcing on Atlantic Tropical Cyclone Activity

We examined the impacts of extratropical forcing on tropical cyclone activity over the Atlantic basin. An extratropical wave train pattern was identified and the pattern affects the large-scale circulation over the extratropical North Atlantic. The variations of extratropical circulation modulate the mass, energy and angular momentum exchange between tropics and extratropics. In certain circumstances, the wave train induces significant changes in moisture and vertical wind shear in the tropical-subtropical North Atlantic, which have direct impacts on tropical cyclone activity. The wave train also affects the Atlantic Hadley circulation, and the latter modulates tropical cyclone activity with mechanisms as have been reported in previous studies.

In some cases, including the year 2013, the extratropical forcing overwhelms the favorable tropical SST conditions and greatly degrades the seasonal forecast skill of hurricane activity. Understanding the linkage between the extratropics and tropics is therefore important for improving the seasonal prediction skill.