Since the creation of the first Typhans, there have always been aquatic worshipers close to Harika and guarding her palace grounds (waters?). These devotees were largely ceremonial; a goddess if more than capable of defending herself, Harika especially. Instead they managed the day-to-day operations of Harika's palace and spread the word of her proclamations as they came.
However, when Harika clashed with the necromancer Xalthar, she found her strength sapped. Not willing to succumb to a wound dealt by a foe so beneath her, Harika retreated to her private dwelling and entered a sort of stasis. There she could remain in a sleep-like state, slowly recovering her strength while also retaining her influence over the seas and storms of Creation. Her Tempest continued to rage on, but Harika no longer directed it with exact precision.
Arash, the Sea Drake was initially charged with directing Harika's followers in the wake of this tragedy. Arash performed admirably but found that he could not be everywhere at once in the vast waters of the Typhans, and so Arash gave the priests, custodians, and guards of Harika duties of more consequence. These changes put greater power in the hands of those close to Harika; they could decide who could enter the palace to offer their prayers and offerings to the slumbering Harika. In such trying times, such spiritual authority increased their power considerably.
With the unexpected capture of Arash by Kross, the priesthood of Harika has become an unchallenged force among the Typhans. While countless Typhan tribes, clans, and kingdoms operate independently of the priesthood, they all must recognize the priesthood as being the ultimate authority on affairs of any significance. For now the priesthood concerns itself with solidifying their control over the waters immediately surrounding Harika's palace, but the groundwork has certainly been laid for greater expansion of the priesthood's "responsibilities."