Japan Meteorological Agency’s Linear Rainband Forecast Success Rate Remains Low at 10％

The Yomiuri Shimbun

1:00 JST, October 22, 2024

The success rate of the Japan Meteorological Agency’s recent forecasts of linear precipitation bands, which can cause catastrophic rainfalls, remains at about 10%, the agency has revealed.

Since the number is lower than the originally expected success rate of about 25%, or one in four cases, the agency said it will examine each case and work to improve accuracy of its forecasts.

The agency’s half-day-before linear rainband forecasts were previously given based on a system in which Japan was divided into 11 regions; however, since May 27 of this year, they have been issued on a prefecture-by-prefecture basis. Between May and September, the agency made 81 linear precipitation band forecasts, eight of which turned out to be correct.

“There were cases in which [linear precipitation bands] didn’t occur for reasons like rainy season fronts not becoming stationary or typhoons passing far away from the coast,” said Takashi Mori, the director-general of the agency.

Meanwhile, the agency failed to predict nine out of 17 cases in which linear rainbands occurred. The success rate was more or less the same as the initially expected rate of one in every two cases, yet the overlooked cases included the linear precipitation band that brought torrential rainfall to the Noto region in Ishikawa Prefecture in September.