Evolution of the surface wind field in an intensifying tropical cyclone

The surface wind field in a developing tropical cyclone (Agnes, 1972) was analyzed over a 1,660 km radius for four days using conventional surface data, as the storm evolved from a disorganized depression to a hurricane. The transition to hurricane intensity was characterized by a wavelike disturbance propagating inward at 15 m s super(-1) from the outermost radii to the storm core over a 36-hour period. This propagating disturbance was clearly visible in the radial and vertical motion fields as a surge of inflow and upward motion. Rapid intensification of the storm began within hours after the leading edge of the surge reached the storm center. The analysis of consecutive 12-hour periods without compositing of data from nonsynoptic times was essential for identification of this feature.