A high pressure system brought clear skies to most of the archipelago on Friday, giving Tokyo and other parts of the country their highest temperatures this year.
The Meteorological Agency said the thermometer registered 29.1 in Toyooka, Hyogo Prefecture, and 28.2 Maizuru, Kyoto Prefecture.
In Tokyo, the mercury rose to 25.1, making it the first summery day of the year, but eight days later than usual.
When the day's high exceeds 25, it is classified as a summery day.
The agency said Tokyo's temperatures since the end of last month have been around 24, about the same as an average year.
The high pressure did not cover Hokkaido or the Nansei Islands in southern Japan. But clear skies will continue until Sunday over Honshu, Shikoku and Kyushu. The front is expected to bring rain to the Nansei Islands.
And, the agency warned, rainy season may be approaching.
In reported rainfall statistics for April, the agency also confirmed what regular nine-to-fivers in Tohoku and Kanto have already noticed -- that rain fell mostly on the weekends.
Five observation sites, including Chichijima Island, recorded the highest rainfall totals ever observed in the month of April.
Overall, the archipelago -- with the exception of Hokkaido, Shikoku and parts of Kyushu -- was warmer than usual last month, the agency said.