I am making a simple micro map and I want to make the Computer's AI storm better. I have Marines & Medics against the Computer's Goons/HTs, but the Computer's AI will only tell the HTs to Psi Storm if the HTs are attacked. I want to have it so the HTs storm pretty well to kill my Marine clumps. Is this possible?
None.
I want it so the HTs will storm without being attacked.
None.
The only way to make computer HTs use storm (along with many other computer-owned spells) is to directly aggravate the unit that can use the spell. I'm pretty sure you
have to attack the HTs in order for them to use their spells.

An artist's depiction of an Extended Unit Death
From the wiki article:
http://www.staredit.net/starcraft/Spells_(Protoss)#Computer_UseComputer Use
High Templars will counter-attack with Psionic Storm to hit any unit that attacks it. They will sometimes move to hit nearby units with a Psionic Storm. High Templars will not hit themselves with Psionic Storm unless they are already near death. Running a melee AI Script will cause the computer to use this ability more.
You can try using a melee AI script to improve your results, but as Demon says, the only reliable way to get them to cast it is if they're attacked.
Edit: Two times in one day. Damn you, Inferno.
I think it's best you refer to
Heinermann's thread.
None.