Objective and Dynamic Analyses of Tropical Weather

Studies concerned with computer methods of analyzing and forecasting tropical weather patterns are summarized. The numerical techniques include a method of making grid-point analyses of winds, a method of balancing divergence fields in the vertical, a procedure for adjusting wind fields to 'fit' cloud patterns, and a tropical forecasting model. Previously, these techniques were applied to synoptic scale analyses in the Caribbean. In this report, they are used to make mesoscale analyses of relatively dense data obtained by the Army in South Vietnam. For the month of September 1967, mean winds in four layers between the surface and 10 km were calculated for the hours 0300, 0900, 1500, and 2100 LST at each station. Objective analyses of these data on a one-quarter- degree latitude-longitude grid show the diurnal wind patterns associated with sea breezes and topographic effects. The variations in the mesoscale divergence fields in the boundary layer are particularly prominent. For this particular region, computed fields of divergence and vorticity in the boundary layer do not show any correlation, contrary to the experience of several other investigators for other tropical areas. Experimental short-range forecasts were made from the objective analyses, and appeared to be computationally satisfactory; however, the model was not able to include the diurnal effects.