The following section contains information from a previous version of StarCraft II which is no longer valid.
Wings of Liberty DevelopmentEdit
The tempest originally appeared early in the alpha phase of StarCraft II. In comparison to the carrier, the tempest was slightly weaker, but cost fewer resources to build. According to Dustin Browder, "the Tempest didn't feel right and that there was too much of an emotional connection with the original unit." In this phase of development, the tempest had a "dark" color scheme, similar to that of the stalker.
Like the carrier from the original StarCraft and Brood War, the tempest had powerful shields and attacked by launching fighter-type drones called shuriken that surrounded and swarmed a target, doing little damage individually but significant damage when combined whilst maneuvering rapidly, making it difficult to destroy. The drones could be auto-built with a right click, a behavior which was carried over to the carrier.
The shuriken made melee attacks.
The tempest was strong against ground targets, but was ill-equipped to handle air-to-air encounters; it had poor air defense as its shields did not activate against air attacks, but the shields took little damage from ground attacks.
Heart of the Swarm DevelopmentEdit
The following section contains information from a previous version of StarCraft II: Heart of the Swarm which is no longer valid.
The tempest was re-introduced in Heart of the Swarm. It initially retained the dark color scheme, but was switched to the "standard" protoss blue and gold coloring, the dark color scheme being passed to the oracle. At its conception, the tempest was put forward as a replacement unit for the carrier, though the carrier has since been implemented in Heart of the Swarm multiplayer.
The tempest was originally designed to handle masses of air units, but was also an effective ground support unit. The tempest launched an orb of energy with area-of-effect damage at airborne targets, and fired a beam of energy at ground targets. However, the anti-air splash was removed, as it was overlapping with the phoenix. Blizzard believes upgrading the phoenix's range will solve the mutalisk problem.
Increases tempests’ range by 12, to a total of 22 range.
The rationale behind the tempest's high range during development was that despite being an aerial unit, it wasn't that different from a colossus or a brood lord. The weapon range (called "strategic range" rather than "artillery range") was thus created to make it stand out from these units more.
The tempest also had an upgrade called Quantic Reactor, researched at the fleet beacon. This upgrade costs 200 minerals and 200 vespene gas. It granted the tempest a +35 damage bonus against massive units. This upgrade was later removed.
Legacy of the Void DevelopmentEdit
In Legacy of the Void, the tempest lost the ability to attack air units through its standard attack, and its role is changed to that of an aerial skirmish unit. However, its movement speed was increased. The changes/abilities were removed in September, 2015, in a beta update, as, in the words of David Kim, the new ability "isn't very interesting." This was compounded by the lack of any counter to the ability, and its application of damage over time led to scenarios where the standard response was "use this unit until it dies." With stronger air units in Legacy of the Void, along with the introduction of the liberator, the tempest was reverted to its Heart of the Swarm version.
Stapleton, Dan. "StarCraft II." PC Gamer Magazine 164 (August 2007): 20-30.