In this paper an attempt has been made to evaluate simulations of Hurricane Dennis performed by using various dynamic cores and initial conditions. Dennis has formed from a tropical wave that moved westward from the coast of Africa on 29 June, 2005. It developed and reached tropical storm strength on 5 July. The storm then rapidly intensified into a Category 4 hurricane with winds of 120 kt. After it reached hurricane strength early on 7 July the central pressure fell to 938 hPa. Moreover heavy rainfall and flooding were the main threat from Dennis, which had one fatality. For the purpose of this experiment the nested Weather Research and Forecasting (WRF) model was used with both the Advanced Research WRF (ARW) core and the Non-hydrostatic Mesoscale Model (NMM) dynamic core as a part of an emerging Hurricane Research Prediction System. The control run was derived from the Global Forecast System (GFS) initial and later boundary conditions. To evaluate the influence of initial condition in hurricane simulations additional experiments were performed by using the Local Analysis and Prediction System (LAPS) as initial conditions. For this purpose in addition to conventional datasets used by LAPS (e. g. mesonet radar, satellites, radiometric profiles, aircraft, etc.) experimental data were included (e. g. GOES/POES Soundings, Cloud-drift winds, Hurricane hunter aircraft ACARS/RADAR wind, and ACARS temperature). The computations has shown over the 48 hr period starting 5 July 2005 at 2100 UTC. Grid spacing for the three specified moving nests will be 18.9, 6.6 and 2.2 km, respectively.