The Storm Dragon is mentioned only once in the How to Train Your Dragon (series), in How to Ride a Dragon's Storm. Madguts the Murderous, leader of the Murderous Tribe, does not speak (he speaks by proxy through Gumboil). There are various theories as to why he doesn't talk, including:

"Some say he lost his tongue wrestling a Storm Dragon with his bare hands."
―about Madguts the Murderous

The Storm Dragon is not mentioned again, nor is any description or information given.