Extended seasonal prediction of precipitation in Fiji

A seasonal rainfall forecasting scheme for Fiji is currently operational, t aking advantage of strong relationships between the Southern Oscillation In dex (SOI) and rainfall in Fiji. In this scheme, the three-month mean of the SOI is used to forecast the immediately following three-month total rainfa ll (e.g. July-September SOI predicting October-December rainfall). In the p resent study, exploratory data analysis is undertaken using correlation coe fficients to determine whether this forecast lead-time can be increased. St rong correlations are demonstrated out to four months in advance for some p eriods of the year. Correlation coefficients between equatorial sea-surface temperatures and Fiji rainfall are found to be higher in many periods of t he year than those between SOI and rainfall. The hindcast skill of a seasonal prediction scheme was then evaluated for l ead-times longer than the currently operational scheme. Strong skill was sh own several months in advance for a few periods of the year, for both predi ctions based on the SOI and on equatorial sea-surface temperatures. This su ggests that the current operational scheme could usefully be extended out t o longer lead-times. For forecasts of the wet season rainfall as a whole, s ubstantial skill was shown in one region of Fiji for predictions made as mu ch as four months in advance.