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RSMC Tokyo-Typhoon Center

Technical Review No.6  (March 2003)

   The Development of Guidance for Forecast of Maximum Precipitation Amount
  Satoshi EBIHARA
   Numerical Prediction Division, Japan Meteorological Agency

 Since 1980, the Japan Meteorological Agency (JMA) has developed various forecast guidance products based on statistics of numerical prediction output to assist operational forecasting. From the disaster mitigation point of view, emphasis is placed particularly on the guidance for precipitation such as Maximum Precipitation Guidance (MaxP) and Area-mean Precipitation Guidance (MeanP), which provide forecasts of respective maximum and area-mean precipitation for 1-, 3- and 24- hour periods for each of about 300 forecast zones designated for information services. The first version of MaxP (hereinafter, the old MaxP) was developed in July 1996 and used until May 2002. In June 2002, JMA developed and put into operation the second version of MaxP (hereinafter, the new MaxP) which was improved especially eliminating the strong bias inherent in the old MaxP toward less frequency in prediction of heavy precipitations. In this paper, an outline of the old MaxP is first presented together with several problems involved in the guidance. Secondly, the process of developing the new MaxP is described and its performance is compared with that of the old MaxP. Finally, an example of forecasts made by the new MaxP for the heavy rainfall associated with a tropical cyclone is shown.
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