It's just turbulence. Without any land to dissipate its energy, a storm such as the great red spot can continue for a stupendously long time- and similar spots tend to appear spontaneously in computer models of gas giants.

So, long story short, it's just there, and it's not actually that special. Read Chaos by James Gleick for a better understanding of the sort of self-organising systems behind it.

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No kidding!!! What do you say at this point?