The rainy season this year is beginning for some western and central parts of the Japanese archipelago weeks earlier than usual, recording the earliest starting date ever in some of these regions since statistics became available in 1951.

According to preliminary figures released by the Meteorological Agency, the Kinki region, which includes Osaka, Hyogo and Kyoto, and other surrounding prefectures, likely entered the rainy season Sunday, 25 days earlier than last year.

The arrival of the rainy season, coming 21 days earlier than average, was the earliest it has begun in Kinki since the agency began compiling statistics 70 years ago. The tentative start date, if unchanged, would break the May 22 record set in 1956 and 2011.

On Sunday, the Tokai region, including Nagoya, may have entered the rainy season at its second earliest date ever and 21 days sooner than usual, the weather agency’s figures showed. In Tokai, the earliest arrival of the rainy season was in 1963 when it began on May 4.

Behind the untimely start of the rainy season in these regions is an unusual trajectory of westerlies that is affecting anti-cyclones over the Pacific Ocean, according to media reports.

The premature start of the rainy season is unfolding nationwide.

Its likely arrival for Shikoku was also announced Saturday by the agency, also the earliest on record. The northern part of Kyushu and the neighboring Chugoku region appeared to enter the wet season Saturday, too, 20 days and 22 days earlier than usual, respectively.

The agency said Sunday heavy rain is expected in western and northern Japan through Monday and warned of possible floods and mudslides.

Past statistics suggest that an earlier start to the rainy season doesn’t necessarily suggest an early end.

In the Chugoku region, for example, the rainy season lasts an average of 43 days, but in 1963, it started on May 8 and continued for 66 days until July 13. In 1991, the season started early on May 25, but lasted until July 21, a span of 57 days.

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