Synonyms for Thunderous (same or very similar meaning)
WordNet sense 1 (loud enough to cause (temporary) hearing loss):
deafening, earsplitting, roaring, thundery
WordNet sense 2 (characterized by or producing sound of great volume or intensity):
loud
WordNet sense 3 (not propitious):
unpropitious
From the ODE community, based on WordNet
add/edit