5 Centimeters Per Second is becoming the third of Makoto Shinkai's exquisite anime works to receive a manga adaptation, after his early OVA
Voices of a Distant Star and the superlative anime film
Beyond the Clouds. Only, this time, the manga isn't drawn by Mizu Sahara (who illustrated the first two manga adaptations), but by Yukiko Seike.

The 5cm per Second manga
begins serialization today, in the July issue of Kodansha's Monthly Afternoon magazine. The same magazine also carried the other two manga based on Shinkai's works, by the way.
Well, that's great and all, but we still crave for more Shinkai anime epicness!