What is the Great Red Spot, solar system's largest storm?

The Great Red Spot on Jupiter is believed to be solar system's largest storm being 16,000-km-wide, big enough to "swallow" three Earths. Models predict the storm gets its reddish hues due to hydrogen, sulphur and ammonia-based compounds. Studied by astronomers since 1600s, an exact cause of the swirling storm with winds peaking at 640 kmph is still not ascertained.