This article refers to a Japanese martial art; if you are looking for Tenmon the composer, see Tenmon (composer)

Ten-mon is the ninja art of understanding and using meteorology as a strategic weapon. It allowed ninjas to foresee weather changes and to use them as an advantage. By knowing nature's changes, animal behaviour, or atmospheric signs, one could use rainy weather or a hot sunny period as strategic elements to weaken and defeat the enemy.

Ninjutsu | Japanese martial arts