Japan seeks to upgrade forecasts of torrential 'guerrilla rainstorms' before 2020 Tokyo Olympics

With an eye on the Tokyo Games, Japanese researchers are developing a new system to accurately forecast torrential downpours — known in Japan as “guerrilla rainstorms” — 30 minutes before they strike.

Scientists have created a high-tech radar capable of producing a three-dimensional map of a rain cloud in 30 to 60 seconds. They say this is a significant improvement on existing systems that measure only parts of a cloud in up to five minutes.

Along with the radar, installed last year at Saitama University, just north of Tokyo, the team is also using radio waves to estimate the amount of water vapor in the air to improve their forecasts.

The waves slow down depending on the volume of vapor in the air, making for a more accurate forecast, said Katsuhiro Nakagawa, director of the Remote Sensing Laboratory at the National Institute of Information and Communications Technology.

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