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1. Introduction
Environmental vertical wind shear (VWS) is one of the most inhibiting factors for tropical cyclone (TC) intensification. Climatological analyses for TCs in different basins consistently show that the stronger the VWS, the smaller the chances of intensification (Merrill 1988; DeMaria and Kaplan 1994; Kaplan and DeMaria 2003; Paterson et al. 2005; Hendricks et al. 2010). The importance of VWS is also evident in statistical-dynamical intensity prediction models, which typically rank VWS as one of the top environmental predictors of TC intensity changes (e.g., DeMaria and Kaplan 1999; Emanuel et al. 2004). However, the likelihood and timing of intensification becomes highly uncertain under moderate VWS (Zhang and Tao 2013; Tao and Zhang 2015), which can be defined as the range of VWS magnitudes that are neither too weak to have little influence on intensity changes nor too strong to completely halt intensification. Intensity forecasts for TCs under moderate VWS are characterized by large errors (Bhatia and Nolan 2013), presumably because other factors-associated with both the TC and its environment-can help offset the negative effects of VWS and lead to intensification. A comprehensive analysis is needed to identify TC and environmental characteristics that are conducive for intensification under moderate VWS.
Certain kinematic aspects of the TC vortex, such as size, intensity, and latitude, can impact intensity changes in sheared environments (Jones 1995; DeMaria 1996; Reasor et al. 2004; Riemer and Montgomery 2011; Tang and Emanuel 2012; Riemer et al. 2013; Reasor and Montgomery 2015). Given that VWS tilts the vortex from its upright position, vortex realignment is a process by which a TC can overcome the effects of VWS and intensify in a sheared environment. Various mechanisms have been proposed to explain vortex realignment, including vortex precession (Jones 1995) and damping of vortex Rossby waves (Reasor et al. 2004). Regardless of the physical mechanism, theoretical and idealized modeling studies agree that large, strong, and high-latitude TCs have faster vortex realignment than small, weak, low-latitude TCs (Jones 1995; DeMaria 1996; Reasor et al. 2004; Reasor and Montgomery 2015). The size and intensity of a TC circulation can also modulate the resilience of a TC to another effect of VWS-dry air intrusion. Large and strong TCs in numerical simulations are less prone to dry air intrusions than...