Summoner AoE is 135 potency every 3 seconds, or 112.5 potency every GCD.

Miasma II adds another ~10 potency every GCD, and tri disaster if you don't have thunder is another 20 potency every GCD.

If there are few enough targets (5 or less) that you can tab target thunder, thats another ~30 potency every GCD.

So around 140 potency every GCD, whether you are tab thundering for <5 targets, or miasma2 + tri disaster for more than 5 targets.