Jupiter's striking "Great Red Spot" is actually a huge anticyclone storm, twice the diameter of Earth. According to NASA, the Great Red Spot has been raging on Jupiter for at least 150 years and is expected to last at least longer. Jupiter's lack of solid ground allows storms to brew for a long time.
The reddish hue of the storm makes the Great Red Spot stand out, but it's not the only storm on this gas giant planet. Other storms will also occur, some starting small (relatively speaking) and later merging into larger, single storms. This is what happened to the second storm, Oval BA, shown above. According to NASA's report, it was formed by three smaller storms that merged in 2000.
This is not the first time NASA has received images of Storm Oval BA. The latest pictures (excluding the new ones in December) - were taken in February 2018. In that picture, the storm appears red; it did not change to the white hue it now appears until recent months.
The original image was taken by JunoCam on Juno's probe at 12:32 p.m. EDT on December 21, 2018, at a distance of 28,000 to 34,500 miles from Jupiter.