A Novel Metric to Improve Predictability in Hurricane Forecast Models: Volume-Integrated Kinetic Energy (VIKE)

We have defined a novel metric, volume-integrated kinetic energy (VIKE), calculated from hurricane forecast models. We have discovered that VIKE provides unique insights into tropical cyclone (TC) intensification, surface wind field expansion, and other metrics related to potential TC hazards, particularly for TCs that interact with land during their life cycle. We constructed partial moist static energy (MSE) budgets for TC forecasts from 3-hourly outputs of the Hurricane Analysis and Forecast System (HAFS) version 1.0 B (HAFS-B). Individual terms of the MSE budget are summed over grid cells with >17 m/s mean wind speed, and over vertical layers of the model from the surface to the highest level of TC vertical alignment. We analyzed a large number of real-time and retrospective forecasts for HAFS-B from 2020-2023, confined only to those cycles and forecast hours that verified reasonably well with track and intensity from National Hurricane Center (NHC) Best Track. For ~170 forecast cycles covering 25 different NHC priority TCs, we find that VIKE is a skillful predictor of potential for intensification. Unlike previously published metrics such as the surface integrated kinetic energy (IKE), VIKE allows an evaluation of the volumetric evolution of a TC. This evaluation permits us to quantify the energy available for potential hazards, improving our understanding of how quickly a TC may recover from detrimental factors such as vertical wind shear, dry air intrusion, a cooling ocean surface, or interaction with land or synoptic features. We further partition VIKE into vertical levels (low-, mid-, and upper-troposphere) and analyze its correlation with other important MSE budget terms, including internal energy, geopotential, and air-sea enthalpy flux. These innovations offer us a deeper understanding of some processes which may complicate the forecasting of TCs and their potential hazards, processes such as coupling with the ocean shelf, and baroclinic interaction with land air masses and upper-level troughs.