THE NUMERICAL PREDICTION OF HURRICANE MOVEMENT WITH THE BAROTROPIC MODEL

Abstract

In order to increase the accuracy of prediction of hurricane movement beyond that which has been obtained with methods now in use, a numerical procedure based upon the barotropic model is presented here. A vortex field is separated from the total flow to obtain the residual-steering flow field. By solving the equation for the steering field, which does not include any parameters related to the vortex, the prediction of the steering flow is executed in the ordinary manner. By solving the other equation, which includes the interaction terms between the hurricane and the steering flow, the movement of the vortex pattern is predicted. To make the latter problem more tractable, a velocity formula for the movement of the vortex center is derived on the basis of a few reasonable assumptions concerning the structure of the vortex and of the steering field. The variables in the formula are expressed only in terms of quantities determined by the steering field and a single characteristic parameter related to the scale of the hurricane. By this means, a forecast of the hurricane movement can be programmed as a subroutine which is executed in the course of the prediction of the steering flow. Five cases of predicting the 24-hour and 48-hour movements of hurricane “Diane” and “Connie” (August 1955) at the 500-mb level are presented here. These results have been obtained by the use of a high-speed computer, from initial maps which were be-analyzed using all available data.