The seasonal powers affect the monster’s hit points. During the season of power the monster gets a percentage increase to its maximum hit points. During the opposite season, it gets a percentage reduction to its maximum hit points.

There are four such abilities:

Strength of the spring: The monster has increased hit points in spring and lowered hit points in autumn.
Strength of the Summer: The monster has increased hit points in summer and lowered hit points in winter.
Strength of the Fall: The monster has increased hit points in autumn and lowered hit points in spring.
Strength of the Winter: The monster has increased hit points in winter and lowered hit points in summer.

How the perenct effect maximum hit points?