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Taking precautions important during torrential rains: JMA

Top: In this image captured from the Japan Meteorological Agency's Himawari 8 weather satellite's real time website, clouds above northern Honshu are seen at 6 a.m. on July 18. (Photo courtesy of the National Institute of Information and Communications Technology) Bottom: This radar image shows the amount of rainfall in millimeters over northern Honshu as of 6 a.m. on July 18. (Photo courtesy of the Japan Meteorological Agency)

With torrential rains having inundated northern Kyushu, and most recently Niigata and Fukushima prefectures, preparations for sudden and intense "guerilla" rainfall and the coming typhoon season have become a necessity even in urban areas.

From the evening of July 17 to the morning of July 18, parts of Niigata and Fukushima prefectures experienced localized heavy rainfall from cumulonimbus clouds that developed after warm air descending from the west mixed with cold air in a pressure trough in the atmosphere. This pattern of cumulonimbus clouds is a phenomenon known as "senjo kosuitai" (linear rainbands), belt-like zones of cumulonimbus clouds bringing torrential rainfall to a localized area in a short amount of time.

According to the Japan Meteorological Agency (JMA), the torrential rain that hit northern Kyushu earlier this month, as well as the Kanto and Tohoku regions in September 2015, were also examples of linear rainbands. The agency says that common indicators of the phenomenon preceding the localized heavy rain, lightning and tornados that come with linear rainbands include the sky suddenly turning dark and cold winds blowing.

When heavy rain falls on flat areas, there is a risk of rainwater flowing into underground areas, like shopping centers in urban areas. The JMA suggests evacuating into buildings to escape downpours, but calls for caution when evacuating, as some underground roads may have been flooded, and the covers for manholes on flooded streets above ground may have also been washed away.

Additionally, while the surrounding area may have clear skies, storms in mountain or upriver areas may lead to heavy downstream flooding. When there are reports of rainfall upstream from your location, the JMA advises residents to move away from riverbanks.

"Even a little bit of water running on the ground surface has the possibility of knocking a person over," said a JMA representative. "In areas where the water has become muddy and you can no longer see where you are placing your feet, you should be extra careful of deeper spots."

At the same time, when in open areas, it is important to be careful of lightning strikes. As a precaution, when lightning strikes a tree or other location, to avoid getting struck from the side by an additional discharge of electricity, it is suggested to stay more than 4 meters away from tall structures such as large trees and electric poles. When there are no nearby buildings into which to escape, it is said that keeping your body posture low to the ground is effective in protecting yourself.

In a 24-hour period stretching until noon on July 19, 80 millimeters of rainfall is expected in the southern Tohoku region facing the Sea of Japan, and 60 millimeters is expected in the area facing the Pacific Ocean. In Tokyo, concentrated rainfall is expected to surpass 30 millimeters in a one-hour period toward the evening of July 18, and the meteorological agency is calling for Tokyoites to take proper safety measures when the cumulonimbus clouds approach the area.

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