Structure and Motion of Tropical Storms in NCEP s Operational Eta Model

Numerical forecasts mainly from NCEP's operational Eta model are currently utilized as guidance to produce short-range (up to 48 h) predictions over the United States. This model is integrated four times daily utilizing a grid spacing of 32 km and 45 layers. Resolvable-scale condensation, parameterized convection, radiational effects, soil moisture and temperature, and explicit cloud water/ice prediction are included. The Eta domain extends over the U.S. mainland and adjoining oceanic areas. Therefore, many tropical storms that affect United States first appear in the Eta domain about 24-48 h before the landfall.

The impact of utilizing synthetic vortex data during the Eta data assimilation (EDAS) cycle will be discussed. Forecast track errors, and storm structure in a few selected cases will be presented. It will be shown that the model performance is better in some cases before than after the landfall. The forecast vertical structure of upward motion, temperature, moisture and other fields will be compared with those produced in EDAS.