Since it appears that Tempest applies Implacable Judgement 9 times, its total maximum damage could be seen as 870 + 225% Bonus Attack Damage. However, it is quite easy to interrupt. Late game, basic attacking with Celerity may do faster damage against single targets, unless you are affected by blinds like Poison Ivy's Blow Kiss.
Since Tempest deals impressive channeled area damage, it combines very well with abilities such as Wonder Woman's Blocking Bracers, which can lock down all enemy champions nearby.
Celerity is the most powerful attack speed boost in the game, allowing Mecha Wonder Woman to outdamage most marksmen if she has it available.
Implacable Judgement can be applied to multiple targets, but has a short duration. It is generally best to focus on a target as it would allow you to repeatedly extend Celerity's duration, greatly increasing your damage output.
Activate Celerity while attacking turrets allows you to take them down much faster, although turrets are unaffected by Implacable Judgement and its Celerity extension.
Afterburn is Mecha Wonder Woman's only disengaging skill, and it has a rather high cooldown especially in early game. Be very careful about using it aggressively. It cannot go through walls.
Use Glaive Storm to harass, although it cannot go through drones. Note that it has the same, fairly long, range as Tempest.