The Gathering Storm is a political entity within the Cenarion Circle whos main goals include maintaining the Balance of Azeroth at all costs, brutal political intrigue and covert activity aimed at destabilising the Horde's military actions.
Led by Winterwind and a circle of close advisors, the Storm seeks to prevent what it deems as "infestation" of Azeroth by alien persons, spirits, ideas and actions in order to allow the natural balance to flourish. This includes the corruption of the Burning Legion, the warped Scourge and the parasitic Orc menace.
For a short time, the Storm was recognised as aligned with the interests of the Horde. The rise of the malefic Deathwing in addition to the departure of Thrall has since convinced its members of the error of that way. As the Circle will not take any side in the Horde/Alliance conflict, the actions of the Storm are by necessity covert.
Its former pawns amongst many races have been cut loose, as the view once taken that these many allies of convenience could be set against one another to promote weakness has been overridden by the new "zero-tolerance" approach. Thus, Death Knights, the Forsaken and Orcish allies have been denounced at spies and traitors, found mutilated or simply dissapeared.