According to Eiga.com, Studio Ghibli announced that their new movie "Kokuriko-zaka Kara" will be premiered next summer. Miyazaki Goro will direct it.

Poster image of Kokuriko-zaka Kara (Toho Film official website)
Kokuriko zaka official website

Kokuriko-zaka Kara is originally a shoujo manga serialized in Nakayoshi magazine in 1980. Miyazaki Hayao loves the manga and Studio Ghibli managed the re-release of the manga this July.

Cover art of Kokuriko-zaka Kara manga (re-released version)

Synopsis:
Adolescence comedy taking place in 1963. Komatsuzaki Umi is a high school girl. She takes care of her brother and sister and manages a western-style lodge next to the sea instead of her mother, who is always away from home. It's about her happy and busy school life with Kazama Shun, a member of the newspaper club, and Mizunuma Shiro, the president of the student council.

Source: Eiga.com

Update on March 8th
According to the movie's official website, the film will be released nationwide in Japan on July 16.

Source: http://www.kokurikozaka.jp/