Developing Hurricane Related Inland Flooding Forecasts at EMC

Tropical cyclones can produce extremely powerful winds and torrential rain, and are also able to produce high waves and damaging storm surge as well as spawning tornadoes. Heavy rainfall brought by tropical cyclones can produce significant flooding inland, and their effects on human populations can be devastating. In the 1970s, '80s, and '90s, more than half of the deaths associated with tropical cyclones in the United States were caused by inland flooding (NHC). Therefore, developing a forecast technique for hurricane-related inland flooding is very important. 2. Methodology A hurricane-related inland flooding forecast technique is under development at Environmental Modeling Center (EMC) by enhancing the HWRF (Weather Research and Forecast system for hurricane prediction) forecast capability with a comprehensive and advanced land surface model (LSM), and linking the HWRF model with the EMC streamflow routing scheme. 2.1 The HWRF model The HWRF is a new computer model for hurricane forecasting developed at EMC. This model was designed to take into account the strengths of the WRF software system, the use of the well-tested NMM dynamic core, and the physics packages of the highly successful GFDL hurricane forecast system. The model is a nested grid system with an 2 outermost domain and a nested grid with resolutions of 27 and 9 km respectively and 42 vertical levels. The HWRF uses a modified 6-hour forecast as the first guess and regional GSI 3DVAR data assimilation for the hurricane vortex initialization. The HWRF is coupled to a high-resolution version of the Princeton Ocean Model for the Atlantic Basin. The ocean initialization system uses observed altimeter observations to provide a more realistic Loop Current and Gulf Stream conditions. The HWRF is running operationally at EMC to produce hurricane forecasts every six hours for up to four tropical storms at a time.