Okinawa Prefecture was hit by heavy rain Wednesday, as a tropical cyclone forecast to turn into a typhoon by Thursday morning approached in the south of the prefecture, the Meteorological Agency said.

The agency issued a warning Wednesday for possible floods, landslides, strong wind and high waves in the southern Kyushu region and other areas of western Japan along the Pacific Ocean.

Osaka, where Japan will host the Group of 20 summit meetings on Friday and Saturday, is likely to be hit by strong rain and wind between Thursday night and Friday morning, possibly affecting flights and other transport.

As of noon Wednesday the cyclone was moving north at 25 kph off the southern coast of Okinawa. It is likely to approach western Japan on Thursday afternoon.

In Nanjo, located in southern Okinawa, 140 mm of rain fell Wednesday morning over the course of six hours. Authorities issued a level 4 rain and flood warning — level 5 being the highest — which requires residents in the city and surrounding areas to evacuate.

The agency also announced Wednesday that the rainy season had arrived in northern Kyushu and the Chugoku, Shikoku and Kinki regions — its latest start in the areas since records began in 1951. Besides Hokkaido, where the phenomenon is not observed, the whole country now appears to have entered the rainy season, the agency said.