for v37 try this.

create a new keymap with multiple steps (1 step for each thunderstorm)
on each step create your /cast thunderstorm macro
the target will be toonA in step 1 toonB in step 2 etc.
on each step, check the delay checkboxes and add your pause's between toons firing off the spells
put the keybinding for this keymap as '1' if you want to have the macros fire off automatically while spam attacking.
if your planing on firing them manually then theres no reason to add the delays as each press of the keybind will cast thunderstorm of a different toon.

as a note, the thunderstorms might not fire off unless you add /stopcasting before the /cast in your macro because you'll probably be casting lighning bolt at the time

hope this is clear and helps, if not then im blaming it on the lack of sleep