The Spell Storing magical armor property states:
This armor allows a spellcaster to store a single touch spell of up to 3rd level in it. Anytime a creature hits the wearer with a melee attack or melee touch attack, the armor can cast the spell on that creature as an immediate action1 if the wearer desires. Once the spell has been cast from the armor, a spellcaster can cast any other targeted touch spell of up to 3rd level into it. The armor magically imparts to the wielder the name of the spell currently stored within it.
1 Immediate rather than swift action as per a designer's unofficial erratum on the message boards.
It clearly says that the armor can cast the spell as an immediate action (assuming it's the wearers immediate)
Does the spell automatically hit since it's a touch attack, and the armor is already in contact with the attacker?