Validation of the HWRF-POM and HWRF-HYCOM hurricane forecasting systems during Hurricane Dorian using glider observations

Hurricane Dorian devastated the Bahamas in August 2019 when it underwent rapid intensification and transitioned from a category 4 to a category 5 storm. The operational hurricane forecasting models consistently under predicted the intensity evolution of Dorian. It has been shown that an accurate representation of the upper ocean processes that affect air-sea heat fluxes in coupled atmospheric-ocean models is necessary for an accurate hurricane intensity forecast. In this work, we evaluate several ocean surface metrics that are relevant to air-sea heat fluxes in one of NOAA's operational hurricane forecasting systems during the 2019 hurricane season: HWRF2019-POM initialized from climatology, and two experimental hurricane forecasting models: HWRF2020-POM and HWRF2020-HYCOM, both initialized from the Real Time Ocean Forecasting System (RTOFS). For this, we use temperature and salinity data from a fleet of autonomous underwater gliders, dedicated to hurricane research and operations, during the passage of Hurricane Dorian through the Caribbean. We contrast our results with estimates from a data assimilative model, the Global Ocean Forecasting System (GOFS 3.1). We found that even though all the models have a good skill in predicting temperature and salinity over the full water column, the model's skill considerably deteriorates for the ocean surface metrics evaluated. We also found that of the three hurricane forecasting models, HWRF2020-HYCOM is the model with the highest skill for the ocean surface metrics. All the models also show a cold bias in the mixed layer temperature and a deficit in the ocean heat content with respect to the glider observations. These results demonstrate that the implementation of HYCOM as the ocean model underneath the hurricane forecasting models, will significantly improve the representation of key quantities that are important for the air-sea heat fluxes during tropical cyclones.