This paper presents the way of identifying the start date of an active storm season in the western North Pacific (WNP) and East Sea (ES). The start (end) date for an active TC season in a year is identified at 5th (95th) percentile of data. Normal and empirical distributions are used to estimate climatological thresholds for the early and late start of the active TC season. Climatological early (late) start is under (over) the date at 33% (67%) of cumulative probability function. Climatological

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... early start is 24 April (20 May) while climatological late start is 28 May (20 June) for the WNP (ES). In the WNP, the start date of storm season tends to be in early and normal (normal and late) phase in post-La Niña (post-El Niño) years. The relationship is not really clear in ES.