Thinking that this would be of some help to them if they are interested in viewing autumn leaves during this period of time.
I have taken some news from 2 different websites for your references.
Little to know:
There are two types of leaves that you could view in Autumn when you are in Japan.
1) もみじ Momiji（紅葉、黄葉）= Red leaves/ yellow leaves Aka Maple Leaves
2) いちょう Ichou（銀杏）= Ginkgo leaves
**I will only cover about the maple leaves.
(Photo taken from: Zekkei Japan)
Weathernews report on September 7th a forecast of the scheduled period where you could have a chance to see the beautiful autumn folic in Japan.
As it is in Japanese only, I will do a simple translation of the article.
(Taken from weathernews.jp)
Is noted that this year due to the extended summer heat wave the autumn leaves will change its color a week later than last year. In Hokkaido, the highest Mountain Asahi have started to change its color.
For this year Autumn, in Sep from Hokkaido to Kyushu due to the late summer heat a wide range of areas are affected, thereafter the temperature will be around the same as last few years. In December, the expected temperature will be lower than the previous year.
Due to this reason, In comparing with previous year forecast which during Sep and Oct viewing of the autumn leaves have been seen at the Highest Mountain In Hokkaido and Northern Japan. This year the possibility of viewing the autumn leaves will be a week later than last year.
As according to the previous year, after Nov it would be the viewing period for East and West Japan, and this year would be the same. In Dec, for Kanto and city area the viewing period will be a little early as always the same as previous forecast.
Tenki Japan report on September 6th
(Taken from: Tenki Japan)
I have done up a translation taken from their website, even though Google can do the job but the English is weird.
|Hokkaido||Expected Viewing Period||Viewing Period (Average)||Average Viewing Trend
|Sapporo(※1)||Late Oct||Late Oct||Same
|Asahikawa(※1)||Late Oct||Late Oct||Same
|Obihiro(※2)||Late Oct||Mid Oct||Late
|Kushiro(※3)||Mid Oct||Mid Oct||Same
|Muroran(※1)||Early Nov||Early Nov||Same
|Hakodate(※2)||Late Oct||Late Oct||Same|
|Northern East||Expected Viewing Period||Viewing Period (Average)||Average Viewing Trend
|Sendai||Late Nov||Mid Nov||Late
|Aomori||Early Nov||Mid Nov||Early|
|Akita||Early Nov||Early Nov||Same
|Morioka||Mid Nov||Early Nov||Late
|Yamakata ||Late Nov||Mid Nov||Late
|Fukushima||Mid Nov||Mid Nov||Same|
East Japan（Koshin・Hokuriku・Tokai Kanto）
|Hokuriku||Expected Viewing Period||Viewing Period (Average)||Average Viewing Trend
|Niigata||Mid Nov||Mid Nov||Same
|Toyama||Late Nov||Mid Nov||Late
|Kanazawa||Late Nov||Late Nov||Same
|Fukui||Late Nov||Late Nov||Same
|Kanto.Koshin||Expected Viewing Period||Viewing Period (Average)||Average Viewing Trend
|Tokyo||Late Nov||Late Nov||Same|
|Mito||Mid Nov||Mid Nov||Same
|Utsunomiya ||Mid Nov||Mid Nov||Same
|Maebashi||Early Dec||Early Dec||Same|
|Kumagai||Late Nov||Late Nov||Same|
|Choshi||Early Dec||Mid Dec||Early|
|Yokohama||Early Dec||Early Dec||Same|
|Kofu||Late Nov||Late Nov||Same|
|Nagano||Early Nov||Early Nov||Same|
|Tokai||Expected Viewing Period||Viewing Period (Average)||Average Viewing Trend
|Nagoya||Mid Nov||Late Nov||Early
|Shizuoka||Mid Dec||Early Dec||Late
|Gifu||Mid Nov||Late Nov||Early
|Tsu||Late Nov||Late Nov||Same|
|Kinki||Expected Viewing Period||Viewing Period (Average)||Average Viewing Trend
|Osaka||Early Dec||Early Dec||Same
|Hikone||Late Nov||Late Nov||Same
|Kyoto||Late Nov||Early Dec||Early
|Kobe||Late Nov||Early Dec||Early
|Nara||Early Nov||Mid Nov||Early|
|Wakayama||Late Nov||Early Dec||Early|
|Chugoku||Expected Viewing Period||Viewing Period (Average)||Average Viewing Trend
|Hiroshima||Mid Nov||Mid Nov||Same|
|Okayama||Early Dec||Late Nov||Late
|Matsue||Mid Nov||Late Nov||Early
|Tottori||Late Nov||Late Nov||Same|
|Shimoneseki||Late Nov||Early Dec||Early|
|Shikoku||Expected Viewing Period||Viewing Period (Average)||Average Viewing Trend
|Takamatsu||Mid Nov||Mid Nov||Same|
|Tokushima||Late Nov||Late Nov||Same|
|Matsuyama||Early Dec||Early Dec||Same|
|Kochi||Late Nov||Late Nov||Same|
|Kyushu||Expected Viewing Period||Viewing Period (Average)||Average Viewing Trend
|Fukuoka||Late Nov||Late Nov||Same|
|Beppu||Late Nov||Late Nov||Same|
|Nagasaki||Early Dec||Early Dec||Same|
|Saga||Late Nov||Late Nov||Same
|Kumamoto||Early Dec||Early Dec||Same|
|Miyazaki||Early Dec||Early Dec||Same
|Kagoshima||Late Dec||Early Dec||Late|
**To note this is only a rough prediction of the autumn leaves period for latest update you will need to visit nihon-kankou. Their system will be updated every Thursday, on the latest condition of the color situation of the autumn leaves.