Ensemble-Based Predictability and Diagnostics of Outflow and Structure Change during the 2017 Atlantic Hurricane Season

A focus of the Office of Naval Research (ONR) Tropical Cyclone Intensity (TCI) initiative is to better understand the role of outflow in tropical cyclone (TC) structure and intensity change. An objective of this study is to use ECMWF ensemble data to diagnose the establishment of outflow channels for 2017 Hurricanes Harvey, Irma, Jose and Maria (and perhaps others), via interactions with the large-scale environment. The influence of these interactions on TC structure change will be quantified, together with their predictability. Conclusions from an earlier study on Hurricane Joaquin (2015) suggested that the predictability of the TC motion and intensification was largely dependent on the initial vortex structure, and that the interaction with an upstream trough was responsible for enhancing outflow in the north-western quadrant and intensifying the hurricane. It remains to be determined whether the outflow plays an active (causal) role in TC intensification, and whether the conclusions can be generalized. The 2017 hurricanes offer an opportunity to explore these questions in more breadth and depth.