NCEP/Climate Prediction Center ATLAS No. 5

A Precipitation Climatology for Stations in the Tropical Basin; Effects of ENSO


A precipitation climatology for 66 tropical Pacific basin stations over the period of 1955-96 has been developed. The main purpose of the climatology is to establish a background for defining thresholds of rainfall def iciency amount and duration associated with drought episodes on an individual island-to-island basis.

Included in the analyses are individual station box-and-whisker plots of se asonal rainfall central tendency (median) and dispersion, the actual season-to-season millimeter amounts and percentiles of rainfall over the 1955-96 period, a rainfall deficiency severity/duration frequency measure derived from those data, and an analysis of the effects of the warm and cold phases of E NSO. A simple ENSO classification system is presented to identify the years having warm and cold episodes. Finally, the spatial distribution of rainfa ll percentiles over the tropical Pacific basin is presented by season for each year of the study period.

The basic data used to perform the analyses shown here are available on the Internet, at location

We anticipate future application of the analyses performed here to the uniq ue needs and characteristics of each island or region, leading to identification of potential drought conditions in forecasts that would otherwise be expressed in a less informative, more generic format such as the probability of rainfall amount being in the bottom third of the distribution for med from a period used as the "normal".

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