The wind in the outer edge of Jupiter's Great Red Spot, the largest storm in the solar system, is speeding up. The change is subtle, about 8% over 11 years, but is significant because these winds are blowing at greater than 400 mph to begin with. Meanwhile, the interior wind speeds have been slowing down. All of these observations are based on observations made by the Hubble telescope of the outer clouds in Jupiter's atmosphere.
The Great Red Spot was discovered by telescope in the 1870s and is more than 10,000 miles in diameter. The storm spins anti-cyclonically, like high-pressure systems do in Earth's atmosphere. In addition to the increase in velocity, the storm has been slowly shrinking and becoming more circular over the past few decades.