The League of Adventurers says:
Whether or not your character is a cleric, if they worship a deity,
you can only choose from the deities listed in the deities of the
Tables Forgotten Realms and Non-Human Deities in the Player's Handbook
or one of the deities listed in the Adventurer's Guide to the Coast of the Sword.
Looking at the back of the PHB, the only well-aligned temepst deity that meets these criteria is Deep Sashelas, the chaotic god of the chaotic good elf. This might require a creative story, but at the strictest reading of the rules, this seems like your only option.
However, in the Adventurer's Guide to the Coast of the Sword, p. 21: "Valkur, god of Northlander seamen; CG; Tempest, War." No dwarf god with the Tempest domain, according to the chart on p.22. SCAG 23: "Aerdrie Feenya, Goddess of Heaven, CG, Tempest, Trickery" in the elven pantheon.
This seems to be a design weakness in Wizards Adventurer League game to require a deity from the sources they list, but to offer a shortage of choice to Dragonborn or Humans clerics (not to mention the purchase of the other book – SCAG). you have more than one choice (odd).