In combining track and intensity estimates from many sources, this centralized collection of tropical cyclone data provides a more complete global climatology and insight into the data uncertainty-a critical consideration for climate trending. Punch cards were once used to encode the earliest hurricane datasets. See the sidebar "A brief history of global tropical cyclone best-track data" on p. 365 for more information.

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technique, 1,000 forecast situations. Results are stratified according a fully computerized objective forecast aid making use of to initial direction and speed of movement of the sample past tracks in forecasting hurricane motion, was developed storms and the number of analogs selected. The utility of prior to the 1969 hurricanc season. Encouraging opera-the technique is discussed, and the importance of position tional results during the 1969 and 1970 hurricane seasons accuracy at forecast time is demonstrated. Initial indicasuggested furthcr evaluation of the technique. To this end, tions of the value of the technique are substantiated.

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The HURRAN (hurricane analog) technique for selecting analogs for an existing tropical storm or hurricane is described. This fully computerized program examines tracks of all Atlantic tropical storms or hurricanes since 1886, and those that have designated characteristics similar to an existing storm are selected and identified. Positions of storms selected as analogs are determined at 12, 24, 36, 48, and 72 hr after the initial time. Probability ellipses are computed from the resulting arrays and plotted on an 2, y (CALCOMP) offline plotter. The program also has the option of computing the probability that the storm center will be located within a fixed distance of a given point at a specific time. Operational use of HURRAN during the 1969 hurricane season, including both its utility and limitations, is described.