Photo/IllutrationFamilies picnic under Metasequoia trees during unseasonably warm weather at a park in Tokyo’s Katsushika Ward on Dec. 4. (Shiro Nishihata)

  • Photo/Illustraion
  • Photo/Illustraion

Many parts of the archipelago experienced their hottest December day on record Dec. 4 as the Japan Meteorological Agency warned of a cold weekend ahead.

The highest temperatures for the month were registered in more than 350 of the agency's 926 observation sites nationwide.

The mercury hit 25 degrees or more in Okinawa Prefecture and Kyushu, along with the Kinki and Kanto regions.

The temperature reached 29.8 degrees in Miyakojima, Okinawa Prefecture, the highest in the country, and Tokyo’s Chiyoda Ward was 23.4 degrees.

The 350 observation points include sites whose temperatures that day matched the previous record set for December.

The cause of the unseasonably high temperatures was southern warm air entering into a low-pressure system moving above the Sea of Japan.

Pressure patterns, however, will become more typical of winter from Dec. 5. The agency forecast the coldest weekend this season so far in eastern and western Japan.