The 23rd Conference on Hurricanes and Tropical Meteorology

11A.6
WORKING TOWARD A CONCEPTUAL MODEL FOR EXTRATROPICAL TRANSITION: DIAGNOSING TRANSITION AND POST-TRANSITION INTENSITY CHANGE FROM OBSERVATIONS AND REANALYSES

Robert E. Hart, Penn State University, University Park, PA

Despite the obvious practical significance of extratropical transition to subtropical and middle latitude climates, the process of transition remains a black box. Further, operational forecasts of transition are notoriously inaccurate. Forecasted regions of flooding rains and damaging winds (both offshore and inland) are often inadequate (e.g. Fran, 1996; Hugo, 1989). Conventional methods for determining the point of transition occasionally fail, such as: reversal of cyclone central temperature anomaly; lack of cyclone central deep convection; loss of an eye structure; dramatically increasing radius of maximum winds. Using a synthesis of observations, reanalyses, and high-resolution (1-10km) mesoscale model (MM5) simulations, we will discuss a conceptual model for transition. We will examine the significant (but not necessary) role of midlatitude troughs, the importance of a gradient of water temperature,and factors that control post-transition intensity change.

The 23rd Conference on Hurricanes and Tropical Meteorology