Griffith Wang of the Civil Air Transport Service, Taiwan, developed a method for objectively predicting the movement of typhoons in the western Pacific. The method is titled A Method in Regression Equations for Forecasting the Movement of Typhoons. The equation utilizes 700-hPa data and is based on the following criteria:

. The 700-hPa contour height and its tendency 10 latitude north of the typhoon center.

. The 700-hPa contour height and tendency 10 latitude from the typhoon center and 90 to the right of its path of motion.

. The intensity and the orientation of the major axis of the subtropical anticyclone which steers the movement of the typhoon.

Percentage of frequency of direction of movement and speed tables are provided for a rough first approximation of the movement of the typhoon. This method, as well as all other methods based on a single chart, is dependent upon a good network of reports and a good analysis. A full test of the value of this method has not been made, but in limited dependent and independent data cases tested it appears to have a good verification and provides another useful tool in the integrated forecast.

Full details on the procedure and application of this method can be found in the Bulletin of the American Meteorological Society, Vol. 41, No. 3, March 1960.

Use of the Geostrophic Wind for Steering

The expansion of aircraft reconnaissance reports have made it practical to carry out more detailed analyses of constant pressure surface over the tropical storm belt and to make use of a forecast based on geostrophic components at that level. This technique, developed by Riehl, Haggard, and Sanborn, and issued as an NA publication Objective Prediction of 24-Hour Tropical Cyclone Movement uses this steering concept. The technique makes use of 500-hPa height averages alongside of a rectangular grid approximately centered on the storm. The grid is 15 longitude, centered at the initial longitude of the storm and between 10 and 15 latitude with the southern end fixed at a distance of 5 latitude south of the latitude of the storm center. A more northward extension of the grid is used for storms found to be moving more rapidly northward. The relatively small size of the grid indicates that tropical cyclone motion for 24 hours is determined to a great extent by circulation features closely bordering the storm, and that the average features outside this area will not greatly affect its movement within the time interval. The 500-mb chart is the basic chart for computations.

Another method that uses the steering concept is A Comparison of Hurricane Steering Levels by B. I. Miller and P. L. Moore of the National Hurricane chart alone.

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