The tempest maw unique axe procs an additional 4 storm sprites when you summon a totem. However, this currently does not happen when you summon a totem via Storm’s aid for Tempest strike or from Stormcarved testament relic or from Boardman’s plank (though these say summon a totem).
If this is actually intended then I would like to give it as a feedback. I think this should not be the case as the axe seems meant for builds using attacks and spells making the mod/proccing totems kinda a waste.