Characteristics of Upper-Tropospheric Jets during Tropical Cyclone Intensity Change

Upper tropospheric jets can impact tropical cyclone (TC) intensity and structure at multiple stages of evolution, from genesis and maturation to extratropical transition. Jets may be detrimental to a TC by imparting vertical shear on the vortex and facilitating lateral entrainment of dry air, but can also interact constructively with a TC through baroclinic forcing of convection, angular momentum fluxes, and increasing outflow efficiency. It can be shown that intensity forecast errors for Atlantic TCs are larger than average in cases where the TC strengthens with a jet nearby, indicating the continuing challenges of reliably predicting intensity changes of TCs in complex environments.

Here, a dataset of jets near Atlantic TCs is objectively constructed from reanalysis data and analyzed in the context of TC intensity change. Subtle differences in jet position, orientation, and structure are found between intensifying and weakening cases. Jets that provide strong dynamical forcing for ascent, and pass close enough to the TC to enhance core convection without being so close as to severely shear the inner core, tend to be associated with intensification more often. The amplitude and extent of flow acceleration in the entrance regions of these jets is also important for modulating upper tropospheric divergence, and thus convective response, near the TC core.

The findings suggest that there is substantial room to improve in TC intensity prediction at short lead times when jet interactions are taking place. The distinction between favorable and unfavorable TC-jet interactions consists of subtle imbalances between competing physical processes that, if can be identified in real-time, could facilitate improvements in forecast skill.