Cyclone Type Analysis and Forecasting: A Need to Re-visit the Issue

The past 40 years have seen significant strides in the forecaster's ability to recognize and diagnose various types of synoptic-scale cyclogenesis in the atmosphere. These include the recognition of hybrid cyclones, the discovery that strong extratropical cyclones could have warm cores, the recognition of a multi-dimensional spectrum of cyclones types, and objectively-based tools to aid analysis and forecasts. The improvements in understanding and techniques have helped forecasters better choose which types of warnings to issue during cyclones that blur the type distinctions.

Operational experience at the National Hurricane Center, however, shows that issues of cyclone type analysis remain in determining if a given cyclone is tropical, subtropical, or non-tropical. These issues include: 1) the strength, organization, and longevity of the associated convection, 2) the horizontal and vertical scales, particularly the radius of maximum winds, 3) the nature and evolution of the thermal structure, and 4) the definition of the circulation center. Case studies of storms off the Florida coast in January 1989, over the New Jersey coast in September 2008, and over the Florida coast in October 2011 highlight the issues involved. There is a need for more insight into the observed structures of these and other similar cyclones to aid the forecasters in real-time, post-storm, and climatologically-related analyses.

It may be possible now or in the near future to create real-time analyses and forecasts of cyclone energetics. This would aid a three-dimensional classification system where the axes would be the three primary driving energies for cyclones – baroclinic, barotropic, and diabatic. This kind of system could aid the forecaster's understanding and ability to forecast hybrid cyclone events. There may also need to be a need for a fourth dimension that takes the scale of the cyclone into account.