The diameter of Jupiter's Great Red Spot has been shrinking about 500 miles a year since 2012. It bears mentioning, however, that, even in its diminished state, Jupiter's ruddy storm system is truly gigantic.
The image above comes from John Brady's "The Size of Stuff," a post at Astronomy Central that uses comparisons like this one to depict the relative sizes of celestial objects. Jupiter's Great Red Spot is, admittedly, currently smaller than it appears here. Upon last assessment, it measured a little over 10,000-miles across. But that's still more than 2,000 miles wider than our entire planet. Sure, the Great Spot may be dwindling – perhaps, even, into nothingness – but it's still the biggest storm in the solar system.