To put it in perspective, when the spot was first properly observed in the late 1800s, it was estimated as 25,500 miles wide - large enough to fit three earths.
The Voyager flybys in 1979 gave a figure of 14,500. Maybe some of that was experimental error, but when Hubble was launched in 1990, the storm was measured again. At 13,020 miles. In 2009, it was 11,130. In the last two years, the great red spot has lost over 1000 miles of width.
It's becoming more circular, too. It used to be oval. The colors are changing. There's a more defined dark circle in the center than there was in 1995.
We don't really understand the Great Red Spot. But we've spent a lot of time studying something very similar on a much smaller scale in both time and space.
Now, the Great Red Spot lacks the spiral arms of an Earth hurricane, but it does have a darker vortex in the center about where a terrestrial hurricane would have an eye. A hurricane is, though, the only thing we can compare it to.
We don't know why it's shrinking. Could it be dissipating? Could it maybe disappear in a few decades?
But here's something else to think about:
This is a NASA video of the formation of a hurricane. You will note there's a point in its formation where it's messy, oval-shaped, with an ill-defined eye. Then as it becomes more powerful, it becomes more circular and the eye becomes clearly visible.
So, I'm going to stick my neck out in a moment of armchair scientist craziness and suggest that far from dissipating, the Red Spot just went up a category and the shrinkage is actually it pulling in on itself as the wind speeds increases.
I'm not a meteorologist, but is that a plausible scenario? (Please, go ahead, prove me wrong - debate is fun!).