There are several synonyms for the phrase "be a roaring success" that can be used interchangeably to convey the same meaning. Some of the popular synonyms include "be a massive hit," "be a runaway success," "be a resounding triumph," "be a blockbuster hit," "be an outstanding success," and "be a phenomenal success." All of these synonyms indicate that something or someone has exceeded expectations and become vastly successful beyond imagination. Whether it's a business venture, a sports team, a movie or book, or anything else, these synonyms can be used to express the extent of its success in an exciting and dynamic way.