How Can Land Surface Processes Impact Track and Intensity Forecasts in the Basin-Scale HWRF?

The Hurricane Forecast Improvement Project (HFIP) is a collaborative effort that aims to reduce track and intensity errors in tropical cyclone (TC) forecasts. One important development of the HFIP focuses on improving the operational Hurricane Weather Research and Forecasting (HWRF) model, which uses two moving nests (9 km & 3 km, respectively) within a static regional domain (27 km) to simulate a tropical cyclone. A parallel version of the HWRF model, called the basin-scale HWRF, is created in the Hurricane Research Division (HRD) at the Atlantic Oceanographic and Meteorological Laboratory (AOML), which is capable of including several moving nests (i.e., more than one tropical cyclone). The basin-scale HWRF model is better-suited for multi-scale interactions and for post-landfall applications. These interactions may modulate the inner core of a tropical cyclone, which ultimately influences its forecast track and intensity.

In the 2015 operational HWRF model, the land surface model (LSM) was upgraded from the GFDL slab LSM to the Noah LSM. However, impacts of the LSM on track and intensity forecast are still unclear. The goal of this study is to quantify the impacts of LSMs on tropical cyclone track and intensity forecasts by using the basin-scale HWRF model. In this study, we use two LSMs that were used in the past and current operational HWRF model. The GFDL slab LSM, which was used in the operational HWRF model before 2014, predicts only soil temperature with fixed land heat capacity and moisture. This certainly limits the capability of the GFDL slab LSM to predict land surface temperature and heat exchanges. On the other hand, the Noah LSM uses four soil layers with a heterogeneous land cover. Surface skin temperature, evaporation and sensible heat fluxes are predicted by the Noah LSM and passed to the atmospheric model. Obviously, the latter more physically reflects reality. Through sensitivity tests on the selected TCs in the Atlantic and East Pacific basins, the impact of these two LSMs on track and intensity forecasts will be assessed in the basin-scale HWRF model. The impacts of LSMs on track and intensity forecasts are further investigated for the landfalling case of Hurricane Isaac (2012).