**Acknowledgements**

resistance to upward vertical motion, forcing subsidence over the storm center [5, 20], but also resistance to adverse effects of the environment, such as vertical shear and Rossby penetration depth, preventing tilting of the TC and allowing for maintenance of the vertical

**•** Divergence at 200 hPa (25kt/24-hours and 30kt/24-hours) showed RI and non-RI cluster composites similar in both spatial location and magnitude of greatest divergence in the northeast quadrant quadrant for the two types of systems. However, RI composites tended

**•** Relative vorticity at 200 hPa for the 25kt/24-hours and 30kt/24rs revealed three RI clusters contained an upper-level area of positive vorticity over the storm center. This feature only appeared for the 40kt/24-hours definition for non-RI systems (which is attributed to occurrence of category 4 TC events). Throughout the mid- and upper- levels, RI cases had

**•** Shear, often thought to hinder TC intensification by creating asymmetry in eyewall convection resulting in a loss of the warm core at upper levels through tilting [24–27], revealed vertical speed shear had a much larger area of statistical significance in discriminating RI from non-RI systems for all RI definitions, compared to vertical directional shear currently

**•** CAPE and skin temperature did not reveal any distinguishing feature between RI and non-RI cases through composite analysis. However, permutation tests suggested the NW and northeast quadrant quadrant of the maps for all RI definitions as statistically significant at distinguishing between storm types for both. Latent heat flux, fundamental in the maintenance of convection and increasing kinetic energy [23, 28], showed that RI systems have higher magnitudes for a larger area over the core, for all RI definitions, and throughout the inflow region for the 25kt/24-hours and 30kt/24-hours definitions. However, land masses could be influencing results at the 1000 hPa pressure level for these three, and the other surface variables; therefore, distinguishing whether these fields are different among RIs and

While results of the RPCA analysis confirm previous findings such as the importance of moisture supply, stability within the core, and stronger relative vorticity for RI systems, it also argues against research findings suggesting magnitude is the main distinguisher between RI and non-RI events [29]. Results presented suggest the symmetry of the equivalent potential temperature and specific humidity profiles throughout the atmospheric column, as well as the storm-centered placement of these variables, and stability, directly over the inner-core (instead of shifted to the east-northeast as with several non-RI composites given lower RI definitions) are significant in discrimination of these event types. While there were some shortcomings, such as proximity to land potentially influencing results in the low levels and the inability to fully resolve the inner-core due to model resolution, the results provide a framework of diagnosis for RI processes within TCs. This framework, combined with an improved statistical modelling scheme, will ideally be of use for improving TC intensity forecasts in operational

significantly higher magnitudes over the storm center, indicating a stronger spin.

thermal structure [24, 25].

used in operational forecasts [1].

non-RIs remains unclear.

meteorology.

to have a statistically significantly larger magnitude.

46 Recent Developments in Tropical Cyclone Dynamics, Prediction, and Detection

This work was funded through the Northern Gulf Institute by NOAA Grant #NA11OAR4320199 at Mississippi State University.
