The Impact of Lightning on Intensity Forecasts Using the HWRF 2016 Operational Model

In 2010, the National Oceanic and Atmospheric Administration (NOAA) created the Hurricane Forecast Improvement Project (HFIP) with the main goal of improving the tropical cyclone intensity and track forecasts by 50% in ten years. One of the focus areas is the improvement of the tropical cyclone rapid intensification (RI) forecasts.  In order to contribute to this task, the role of lightning during the life cycle of a tropical cyclone using the NCEP operational HWRF hurricane model has been investigated.We ask two key research questions: (1) What is the functional relationship between atmospheric moisture content, lightning, and intensity in the HWRF model?  and (2) How well does the HWRF model forecast the spatial distributions of lightning before, during, and after tropical cyclone intensification, especially for RI events?In order to address these interrogates, a lightning parameterization scheme called the Lightning Potential Index (LPI) was implemented into the HWRF 2016 operational model. The study cases selection criteria were based on tropical cyclones with intensity forecast degradation when HWRF 2016 was executed retrospectively. The selected study cases to test the LPL implementation on the HWRF 2016 are: Humberto, Jerry, Karen, Arthur, Bertha, Cristobal (North Atlantic); Erick, Karina, Polo, Rachel, Simon, Vance (East Pacific); Atsani, and Mujigae (West Pacific). Five-day forecasts were executed on each case study with emphasis on intensification periods.  An extensive analysis between observed “best track” intensity, model intensity forecast, and potential for lightning forecast was performed. Preliminary results   are showing that:  (1) strong correlation between lightning and intensity changes does exists; and (2) the potential for lightning increase to its maximum peak few hours prior the peak intensity of the tropical cyclone.LPI peak values could potentially serve as indicator for future intensification periods. Results from this investigation provide a better understanding of the mechanism behind lightning as a proxy for tropical cyclone steady state intensification and tropical cyclone rapid intensification processes. Lightning forecast has the potential to improve HWRF hurricane model intensity forecasts.