NASA Unified Weather Research and Forecasting (NU-WRF) Model Simulations for the Brown Ocean Effect: A Case Study of Tropical Cyclone Kelvin (2018)

A suite of numerical simulations of Tropical Cyclone Kelvin has been conducted using the NASA Unified Weather Research and Forecasting (NU-WRF) coupled with the NASA Land Information System (LIS) to understand the contributions of the latent heat fluxes (LHFs) from the land surface for the landfalling tropical cyclone to maintain or intensify its strength after its landfall. Since its development as a tropical low system over Tiwi Islands north of Darwin, Australia, the system travelled southwest along the northwestern coast of Australia, precipitating substantial amount of rain over the cluster of national parks in the northern part of the Western Australia. The system intensified into Category 1 Cyclone over the shallow Indian Ocean shore near Eighty Mile Beach on Feb 17, 2018. Cyclone Kelvin (2018) made its landfall in the evening on Feb 17, 2018 through the Eighty Mile Beach while its strength increased to Category 2. The system survived over the desolate land with relatively barren soils until Feb 19, 2018 when it became a Tropical Low. Among the suite of eleven numerical simulations driven by three global datasets (i.e., ERA-Interim, GDAS (FNL), MERRA2), the NU-WRF coupled with the LIS model simulation driven by the GDAS data produced the closest results to observation in terms of its track and intensity.

Model simulation analysis reveals that the Tropical Cyclone Maintenance or intensification (TCMI) was highly associated with the latent heat flux (more than 70 W s^-1) over the land surface precipitated by the system itself over the national park cluster region as well as about the center of the cyclone during the daytime. Vegetation condition over the national park cluster are also considered attributable to enabling the Brown Ocean Effect in the case of Kelvin.