Japan's Kanto region is under a Level 3 heavy-rain warning with the most intense precipitation expected tonight [1].

The weather system poses a risk of localized flooding and travel disruptions across several prefectures, including Saitama, Tokyo, and Kanagawa. Residents are advised to monitor conditions as the rain peak occurs during the night of June 20 [1].

According to reports from ANNnewsCH, the rain is currently intensifying specifically around Saitama prefecture [1]. The Japan Meteorological Agency said the volatility is due to a stationary rain front lingering south of the Kanto region [2]. This system is interacting with a cold high-pressure system approaching from the Okhotsk Sea, which is intensifying the rainfall and causing temperature fluctuations [2].

Forecasters expect the initial peak to subside by tomorrow morning, but another round of precipitation is possible. A second rain shower may occur on the night of June 21 [1].

Following the rain, the region will experience a significant shift in temperature. Tokyo is forecast to reach a high of 28 °C on June 22 [1]. However, as the cold air from the Okhotsk Sea flows in from the north on June 23 and 24, temperatures will drop notably [1].

By June 24, the forecast high for Mito is expected to be 21 °C [1]. Similarly, Yokohama is projected to reach a high of 22 °C on the same day [1].

Weather forecaster Junko Miyake said that while the Kanto region saw some sunlight before noon, the weather will remain unstable throughout the afternoon [2].

“Level 3 heavy-rain warning issued for parts of Saitama prefecture”

The interaction between a stationary rain front and the Okhotsk high-pressure system creates a volatile weather pattern characterized by rapid transitions between heavy rain and cooling trends. This suggests a period of instability for the Kanto region where residents must prepare for both flash-flood risks and a sudden drop in temperature within a four-day window.