The movement of the Atlantic hurricane of September 11–20, 1947, into the Gulf of Mexico rather than up the Atlantic Coast, is attributed to dynamic anticyclogenesis over the eastern United States. An attempt is made to explain this anticyclogenesis by the transfer of energy downstream from the mid-Pacific at a rate considerably greater than the speed of individual air particles. The motion and change in intensity of 700 mb trough and ridge systems are discussed in terms of constant absolute vorticity, horizontal temperature advection, and the process of confluence. It is concluded that the large-scale features of the hemispheric circulation are of great importance for short-range, as well as for extended, weather forecasting.

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