You probably know that Tokyo's temperature and rainfall are observed at the instrument enclosure (rojo) of the Tokyo Regional Headquarters of the Japan Meteorological Agency in Otemachi. That regional headquarters, together with the Japan Meteorological Agency, had been scheduled to move around next fiscal year to the former Tomoe Elementary School site in Toranomon, Minato Ward. Because the Otemachi site is to be disposed of, the enclosure would have to move as well.
Tokyo's weather observations were taken from 1882 (Meiji 15) to 1923 (Taisho 12) at Kitahanebashi of the former honmaru of the Imperial Palace, from 1923 to 1964 (Showa 39) near today's Takebashi Kaikan, and since 1964 at the present site. In other words, they have been carried out around Takebashi for about 130 years. Even if the regional headquarters moves, observations should continue in the same area to monitor climate change, so the enclosure will be relocated to Kitanomaru Park on the opposite side of Palaceside Building.
Ahead of the headquarters' move, a new enclosure was completed last summer about 100 meters west of the Science Museum in Kitanomaru Park, and trial observations have been running since August 1 of that year. According to the regional headquarters, about one year of data shows that average and minimum temperatures are slightly lower in Kitanomaru Park than at the current Otemachi enclosure, humidity is slightly higher, and differences in maximum temperature and precipitation are almost none.
The Tokyo Regional Headquarters says it will use the differences from three years of observations starting last August to improve future weather observation. The headquarters move, however, is well behind schedule, and at this point no one knows when it can take place, so it is also undecided when Kitanomaru Park readings will be adopted in earnest as Tokyo's official weather data. Still, one way or another, the weather data around Palaceside Building will be Tokyo's weather data.