If your principal uses stentorian tone she is

loud

jaunty

prodigious

loud

Explanation:

A stentorian tone is an extremely loud tone, although perhaps a more appropriate synonym for the word would be deafening or booming since stentorious implies louder even than loud.

The voice of the principal then would have been thundering, most likely because he/was angry or because the distance obliged him/her to use as much volume as possible.