臺灣夏季六至十一月的月與季雨量預報極為重要。尤其是在水資源緊縮的現實壓力下，任何具參考價值的預報資訊均彌足珍貴，本研究開發了一個以西北太平洋臺風生成個數來預報臺灣夏季雨量的簡單方法，可以在五月底預估當年六至九月的雨量類別特徵，也可以在八月底預估十月和十一月的雨量類別。依區域氣候記號強度來看，最具參考價值的預報情境是：若一至五月西北太平洋臺風個數偏多則臺灣北部的七至九月累積雨量偏少。 2003年的事後預報結果顯示本模式的季雨量預測是正確的，環流分析結果也支持了這個正確性，比較一至五月西北太平洋臺風個數偏多年和北臺灣偏乾年雨類的850hPa環流合成距平，以及2003年的環流距平，我們發現當一至五月臺風個數偏多時南海與西太平洋上在四、五月就出現明顯的低壓環流，並可持續到盛夏；伴隨此低壓距平在六至八月25°N附近的太平洋副高脊偏強，臺灣與臺灣以東的西太平洋高壓環流偏強，在臺灣西邊的臺灣海峽和福建一帶則有南風距平。然而按臺灣北部夏季偏乾所合成的環流距平顯示從西太平洋伸入南海的副高脊在四、五月偏強並且範圍甚廣，從菲律賓海經南海至華南以北等大範圍均被涵蓋在異常高壓環流的範圍內，六至八月在15°N附近西太平洋副高脊持續偏強，西太平洋暖池近赤道區有偏強的東風。2003年的環流特徵比較接近一至五月西北太平洋臺風個數偏多年，25°N附近副高偏強，與典型偏乾年有明顯的差別。因此，一至五月臺風個數偏多可視為偏乾年中一組特別族群，颱風個數偏多是判斷臺灣北部夏季偏乾的一個重要前兆，2003年個案即為一例。唯有區域氣候記號顯著的部分才可以預報，因此本文提出的預報方法特別強調明確規範預報模式的適用條件與對象的重要性，同時也為如何以臺風個數預報產品預估臺灣夏季雨量類別指出一個方向。

　　　　　The months of June to November are the main raining season in Taiwan. The monthly to seasonal rainfall predictions for this season is of particular importance. In this study, we present a simple prediction model. The predictors are the Northwest Pacific typhoon numbers and the predictands are the Taiwan summer rainfall category in different months. We find that the monthly, bimonthly and tri-monthly rainfall during the period of June-September can be skillfully predicted in May, and the October and November rainfall can be predicted in August. The prediction scenario with the highest confidence is: if the total typhoon number in January-May is above normal, then the accumulated July-September total rainfall in north Taiwan will be below normal. The usefulness of the prediction model is demonstrated by the hindcast results of 2003. The composite 850hPa wind anomalies respectively for the years of more typhoons in January-May and for the years of dry north Taiwan are compared. During the years with more typhoons, anomalous cyclonic circulation is observed over the South China Sea and the western Pacific warm pool near the equator. The anomalous circulation appears in April or May and lasts until September. To the north of the anomalous cyclonic circulation there is the anticyclonic circulation over the western Pacific near Taiwan with the anomalous ridge sitting around 25°N. For the years of dry north Taiwan, the anomalous circulation patterns are very different from the more typhoon years, except that the subtropical high near Taiwan is particularly strong. The position of the anomalous ridge of the Pacific subtropical high is at 15°N. The anomalous circulation pattern in 2003 is more similar to the more typhoon years than the typical dry years. Thus, the 2003 case suggests that the total typhoon number in January-May can be taken as a useful precursor for the dry summer season in north Taiwan. Climate prediction can be done only when the regional climate signal is strong. It is important to note that all climate prediction model need to provide the information about in which time frame and in what area the regional climate signals can be skillfully predicted. Our results also have the potential to be used as a tool for applying the predicted typhoon numbers in predicting Taiwan summer rainfall.