Short answers, pulled from the story.
The Great Dark Spot, designated GDS-89, was a massive anticyclonic storm observed in Neptune's southern hemisphere by NASA's Voyager 2 in 1989. It was roughly the size of Earth and is thought to be a hole in Neptune's methane cloud deck. Winds at its edges reached 2,100 kilometers per hour, the fastest recorded in the Solar System.
The Great Dark Spot had disappeared by November 1994, when the Hubble Space Telescope attempted to photograph it. Astronomers concluded it had either dissipated or been covered by other cloud features.
Winds measured around the edges of the Great Dark Spot reached up to 2,100 kilometers per hour, or approximately 1,300 miles per hour. This was the fastest wind speed recorded anywhere in the Solar System.
Jupiter's Great Red Spot has lasted for hundreds of years and is locked in place by global east-west wind currents. Neptune's Great Dark Spot shifted north and south over time and appeared to last only a few years before dissipating. Neptune's dark spots also have relatively cloud-free interiors.
The companion clouds around the Great Dark Spot are made of crystals of frozen methane, not water ice as with Earth's cirrus clouds. They form near the tropopause layer, between 50 and 100 kilometers above the main cloud deck, and were observed to persist for at least 36 hours.
Several dark spots have been observed since 1989, including a Northern Dark Spot in 1994, another in 1996, a Southern Dark Spot found by the Hubble OPAL program in 2015, and a new storm documented from birth in 2018 that measured approximately 4,600 miles across. The Hubble Space Telescope is the only instrument currently able to detect these features.