Improving Physical Parameterizations of the Operational Hurricane Weather and Research Forecast (HWRF) Model Using Aircraft Observations

This talk presents results of research to opearation in terms of improving the physical parameterizations of the operational Hurricane Weather and Research Forecast (HWRF) model using research aircraft observations. This work was supported by NOAA's Hurricane Forecast and Improvement Project (HFIP). We demostrate the usefulness of a model physics developmenal framework that includes four steps: 1) model diagnostics against observations; 2) new physics development using observations, 3) new physics implementation, and 4) further evaluation of the new physics. We first briefly summarize our published resluts of the successfulness of applying this framework to improve the surface-layer and boundary-layer parameterizations of the HWRF model. We then focus on discribing our recent physics upgrade of the horizontal diffusiion in HWRF based on observational data. A series of sensitivity experiments were conducted to forecast rapidly intensifying Hurricane Earl (2010) in a sheared environment by varying the horizontal mixing length in the 2015 version HWRF model (H215), while keeping other physics packages unchanged. We found that the observation-based setup of horizontal mixing length which is much smaller than that used in H215 gave the best foreast of Earl in terms of intenisty and multi-scale structure. Implementation of observation-based horizontal mixing length in the 2016 version HWRF (H216) led to substantial improvemnts in the intenisty forecasts according to independent retrospective runs of Hurricanes Edouard (2014) and Gonzalo (2014). This work will provide guidance for further improving other aspects of the HWRF model.