2018 cherry blossom forecast

I have noticed that this website is showing first bloom and full bloom for certain cities as happening much later than other official forecasts that are being posted online. Even though the date of the status updates on this site are showing as current. For example, other websites are showing Sendai as having full bloom on the 7th of April. This website shows best viewing dates are 11th - 19th April.

Does anyone know why this site has such a difference?

Since Japan's Meteorological Agency stopped issuing sakura forecasts about 10 years ago, there have been no "official" forecasts! Instead, there are now multiple forecasts by private weather companies. And their forecasts differ. I am wondering what "official forecasts" you are referring to.

As explained on the forecast page, the forecasts for opening days by japan-guide.com are based on those by the Japan Weather Association, the oldest such company in Japan (while the period of best viewing is forecast by japan-guide.com):
https://tenki.jp/sakura/expectation/

The other major source is Weathermap:
https://sakura.weathermap.jp/

The difference for Sendai between the two services is 2 days which I consider minor. As for Aomori, it is not even listed on japan-guide.com.

Note that there are; however, a large number of English websites that never update their forecasts or have no idea what they are talking about. I hope you are not considering one of them to be "official".

In English, both WeatherMap and Nihon Kisho expect the same date: Mar 30(first bloom) - Apr 5(full bloom).
https://sakura.weathermap.jp/en.php
https://n-kishou.com/corp/news-contents/sakura/news2018.html?lang=en

In Japanese, Tenki forecasts a bit later, Apr 1 - Apr 7.
https://tenki.jp/sakura/expectation/

WeatherNews has three sites in Sendai City. All are much later.
Nishi Koen (Aoba Ward): Apr 7(first bloom) - Apr 10(50% bloom) - Apr 12(full bloom) - Apr 19(Sakura blizzard). https://weathernews.jp/s/sakura/spot/53/index.html
Tsutsujigaoka Koen (Miyagino Ward): Apr 6(first bloom) - Apr 10(50% bloom) - Apr 12(full bloom) - Apr 19(Sakura blizzard). https://weathernews.jp/s/sakura/spot/55/index.html
Mikamine Koen (Miyagino Ward): Apr 9(first bloom) - Apr 11(50% bloom) - Apr 13(full bloom) - Apr 20(Sakura blizzard). https://weathernews.jp/s/sakura/spot/3407/index.html

A WeatherReporter sent a photo of no bloom in Tsutsujigaoka Koen to WeatherNews on Mar 31.
https://weathernews.jp/s/sakura/gallery/repo.html?repoid=41429734&name...

Kahoku Shinpo reported Sendai Kanku Kishodai (the official) announced the first bloom in Sendai on Mar 30. It also said full bloom would be on Apr 4.
http://www.kahoku.co.jp/tohokunews/201803/20180330_13060.html

The sampling sites are different. The forecasting algorithms should also differ. I do not know which could be the representative of the whole city in the end.