The mercury soared to 36.6 in Maebashi, Gunma Prefecture, and 32.9 in Tokyo on Wednesday, marking the highest temperatures in the Kanto region so far this year, the Meteorological Agency said.
The agency predicts the Kanto and Tokai regions will see some rain starting around Friday, ending an unusual spell of dry weather for the rainy season.
Areas on the Sea of Japan coast saw heavy rain, prompting the agency to issue flood and lightning warnings Wednesday in Niigata Prefecture and other areas.
The Japanese archipelago entered rainy season starting with the Okinawa region May 10, followed by northern Kyushu and Kanto-Koshin on June 3 and Hokuriku and Tohoku on June 7.
But clear weather has since prevailed over most of the nation, except for some areas in western Japan.
Precipitation recorded from June 1-13 in the Kanto-Koshin region was 77 percent below average and 76 percent below average in Tokai, the agency said.
Meteorologists said a rain front was hovering in the ocean just south of the archipelago during the first half of June but that a Pacific high-pressure system was not powerful enough to push it north, resulting in fine weather.
Although the rain front moved north Wednesday, it inexplicably passed over the Kanto region "for some reason," agency officials said.
Temperatures in southern Kanto will continue to soar today and are expected to exceed 30 degrees.