The 3-month total precipitation data were assembled from 1-month data, much of which was obtained from the National Climatic Data Center (NCDC) in Asheville, North Carolina in the mainland U.S. Much of the remainder of the data came from a global network of monthly observations (CAMS; Ropelewski et al. 1985). Some of the data were also obtained from the Pacific Region of the NWS and from the National Institute of Water and Atmospheric Research Ltd (New Zealand). Finally, some data were obtained directly from island Weather Service offices; specific individuals are recognized in the acknowledgments.

While data for the entire 1955-96 period was available at many stations, this was not always the case. Where data for certain months was missing, these were filled in using interpolation from the rainfall data of the few nearest neighbors. In this process, the inverse distance-weighted mean of the standardized rainfall anomalies of the neighbors was damped (to reflect uncertainty) and converted to equivalent rainfall amounts at the missing location. The number of cases for which this filling-in process was required is not large, as shown in Table 1. Specifically, 48 of the 66 stations had 100% of data available, and all but 1 station had at least 90 percent of data available. It should be noted that it is possible that some of the data that were apparently not missing may have been missing originally, and previously filled in by others at one of the sources listed above. Additional stations could have been included here if the requirement for the percentage of data present had been relaxed further, but it was decided that the reliability of the results would be compromised by a greater amount than the benefit brought about by the increased spatial resolution.