Are NCEP Seasonal Forecasts Useful in New Zealand? | The Meteorological Society of New Zealand

Are NCEP Seasonal Forecasts Useful in New Zealand?

R.I.C.C. Francis
J.A. Renwick

There is growing interest, and activity, in seasonal climate forecasts, on both global and local scales. In New Zealand, seasonal forecasts have been produced by NIWA and issued to the public regularly since mid 1999. Such forecasts have obvious potential economic value in industries like agriculture and energy generation. A possible source of guidance for local forecasts is the set of global extended range forecasts produced by major international agencies. This paper evaluates one such source: seasonal forecasts of 200 hPa heights, surface temperature, and rainfall produced by the National Centers for Environmental Prediction (USA) for the three year period 1997 to 1999, inclusive. Two classes of forecasts are found to be more skilful than both persistence and climatology: 200 hPa heights in the tropics outside of the Pacific, and surface temperatures in the eastern tropical Pacific. Over much of the middle latitudes, including New Zealand, forecasts are found to have little skill compared to use of a climatological mean state. Model forecasts do display skill compared to persistence forecasts. For New Zealand, forecast utility seems limited to predictions of the state of ENSO, which can be combined with local statistical information in the generation of climate outlooks.

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