The Relationship between Tropical Cyclone Vortex Tilt, Precipitation Structure, and Intensity Change

Vertical wind shear, which is ubiquitous in the atmosphere, can act to misalign, or tilt, the lower and upper portions of a tropical cyclone (TC) vortex. Previous observational studies have shown that many weak TCs (e.g., those at the threshold of hurricane intensity and below) can be severely misaligned, whereas mature TCs tend to exhibit much smaller tilt magnitudes. The role of vortex alignment, however, in the TC intensification process is not clear from previous work. For instance, some studies have concluded that vortex alignment acts as the trigger for TC intensification, whereas others have hypothesized alignment occurs as the result of intensification. Part of the uncertainty of the role of vortex alignment arises from the lack of a systematic observational analysis of the relationship between vortex tilt and TC intensity change. To address this gap, this presentation explores a recently-introduced database of over 1,000 airborne Doppler radar analyses, referred to as the Tropical Cyclone Radar Archive of Doppler Analyses with Recentering (TC-RADAR). Here, we will show that a robust relationship exists between the vortex tilt magnitude and subsequent TC intensity change, but only in relatively weak TCs. To better understand this relationship, the precipitation characteristics of two groups of weak TCs will be investigated: 1) small-tilt and 2) large-tilt TCs. We hypothesize that small-tilt TCs intensify at greater rates than large-tilt TCs due to a greater areal extent of diabatic heating near the lower-tropospheric TC center and inward of the storm’s radius of maximum wind. These results are consistent with the hypothesis that vortex alignment acts as a trigger for greater rates of TC intensification.