Atmospheric Boundary-Layer Properties Affecting Wind Forecasting in Coastal Regions

Atmospheric boundary-layer properties and processes in gulf and coastal regions have special characteristics that are important in forecasting winds and ocean forcing. Accurate coastal-wind predictions require knowledge of local responses to a given synoptic-forcing scenario. The Overwater surface roughness effect on wind stress, specified by a neutral drag coefficient, for a 15 m s−1 surface wind averages 25% higher in coastal regions than in open-ocean regions. The change in sea state associated with a sharp sea surface temperature gradient (front) caused a 10%–20% increase in neutral drag coefficient. Sea-state and wind-wave orientation changes associated with an atmospheric cold front increased the neutral drag coefficient by a factor of 2 for a 3–4-h period following the frontal passage. The effect of increased drag coefficient on surface wind speed is to slow it down by an amount that depends on the height of the inversion base and other processes within the boundary layer. An example of a coastal jet shows complications in the wind field associated with horizontal air temperature changes in the atmospheric boundary layer.