Are Rapidly Intensifying Tropical Cyclones Associated with Unique Vortex and Convective Characteristics?

Abstract

The largest tropical cyclone (TC) intensity forecast errors are typically associated with episodes of rapid intensification (RI). Here, we explore whether TCs that undergo RI are associated with different vortex and convective characteristics compared to TCs that are either slowly intensifying (SI) or nonintensifying (NI). Because characteristics of TC structure are strongly linked to intensity, a normalization technique is employed to examine how the anomalous TC structure, relative to the average structure for a given intensity, is related to TC intensity change. TC structure is assessed using a recently developed database of airborne Doppler radar analyses collected by NOAA'sWP-3D aircraft over the last three decades, primarily in the North Atlantic basin. We find that RI episodes are associated with significantly taller and narrower primary circulations than both SI and NI episodes. RI episodes also tend to occur in storms with anomalously deep overturning circulations and larger azimuthally averaged ascent in the upper troposphere than SI and NI episodes. Additionally, the inner core of RI TCs exhibits a significantly greater areal coverage of convective bursts, which are defined as locations with relatively vigorous ascent in the mid-upper troposphere. Ultimately, TC intensity change is governed by multiscale processes, and RI is found to occur preferentially in TCs that have both favorable synoptic-scale environmental conditions and favorable vortex structures for intensification. Consequently, observations of the anomalous TC structure may serve as useful predictors for TC intensity change and RI.