Determination of a Consistent Time for Extratropical Transition of Tropical Cyclones

Extratropical transition is a process that many tropical cyclones undergo as they move north out of the tropics over colder waters or land and interact with an area of higher baroclinicity and often a mid-latitude trough. In many cases, the tropical cyclone is influenced by the approaching trough and may interact with the preexisting extratropical low adjacent to the trough causing the low to intensify. Although there has been a recent increase in the study of physical processes associated with tropical cyclones as they transition into extratropical cyclones, there has been no advent of a common definition of extratropical transition that is consistent across all cases. Such a definition may have utility for the operational community by providing a standardized time to designate extratropical transition. There would also be several benefits for the research community, not the least being a consistent designation in the best track records for extratropical transition with an associated criteria that is understood by everyone. The existing definitions of extratropical transition include descriptions of the structural evolution of the tropical cyclone during extratropical transition using satellite derived data and global gridded datasets, the progression of an axisymmetric warm-core system to an asymmetric cold-core system via phase-space, frontal cyclogenesis, and other spatial and temporal distinctions.

In this presentation, we will show a comparison of the strengths and weaknesses of the different definitions of extratropical transition and assess their utility for research and operations. Our ultimate aim is to determine a common definition that can be simply understood for operational purposes but still include enough description of dynamical behavior of extratropical transition of tropical cyclones to be used for more complex and in-depth research.