Validation of the coupled NCEP mesoscale spectral model and an advanced land surface model over the Hawaiian Islands

The National Centers for Environmental Prediction (NCEP) Mesoscale Spectral Model (MSM) coupled with an advanced Land Surface Model (LSM) is used in assessing the impact of the improved representation of island terrain and surface boundary conditions on simulating orographic effects and local circulations under various large-scale settings.; The surface variables predicted by the operational 10-km Regional Spectral Model (RSM) during a one-month period of 20 May through 20 June 2002 agree well with observations over the buoy stations in the Hawaiian waters. Over land with adequate representation of the terrain, the 1.5-km MSM provides better forecasts of surface variables than the 10-km RSM. Further improvements are achieved by coupling the MSM with the LSM. In particular, over-estimation of the surface wind speed and daytime cold biases in the MSM are largely corrected in the coupled MSM/LSM. The observed composite diurnal cycles of surface variables are also better forecasted by the MSM/LSM than the MSM.; Evaluations of the 3-km MSM/LSM simulations are performed for sea breeze cases during 23 June to 28 June 1978 over northwest Hawaii. Except for 27 June, the model predicted onset time, duration and vertical extent of the sea breezes agree with observations. Sensitivity tests using the MSM/LSM demonstrate the non-trivial effects of surface properties and initialization processes on sea breeze behavior.; Heavy rainfall and high wind events over the Hawaiian Islands display a large variability in rainfall and wind distribution related to complex terrain and local winds. The 10-km RSM/LSM reasonably resolves regional-scale weather features associated with significant synoptic systems but fails to accurately reproduce rainfall distribution and rate, and orographically amplified strong winds. The MSM/LSM, with its higher resolution (≤3 km), has better capability in simulating localized rainfall distributions and airflows associated with these heavy rainfall and high wind events.; Major model bias is that the MSM/LSM produces excessive rainfall on the windward side of steep mountains with little rainfall downstream of the mountain ranges.