8 Foot T8 "Standard Bi-pin" Lamps (430 ma Lamps) are - for lack of a better term - Dogs!
The Capacitive "Cork-Screw" effect will reduce in time, to a point where it is not noticed.
As mentioned, the Swirling Effect is a common phenomena where Lamps are exposed to low Temperatures.
The Lamps, in a way, are suffering from Hypothermia - they cannot produce enough heat to sustain a solid Plasma, so the Plasma does not fill the entire Lamp Envelope.
The Cold Ambient Air surrounding the Lamps draws larger heat quantities away from the Lamps, which directly affects the Illumination Wattage of the Lamps - resulting in lower Light output.
Similar results occur where the Ambient Temperature is hot, only in this case the Lamps absorb heat.
Program-Starting of HO & VHO Lamps - via Hot Cathode Operation, tends to reduce these issues.
Have the Client leave the Lamps operating continuously for at least 8 Hours per day, no less than 5 consecutive days.
If the issue remains unchanged after this period of Lamp Initiation, AND the swirling is a valid issue (read: critical to safety / task, not simply a "Peeve"), consider changing to either 8 Foot T8 HO/VHO Lamp-Ballast setup,
instead of the 8 Foot T8 Lamp, use (2) Four Foot T8 430 ma Lamps with an Instant Start Ballast, in place of (1) Eight Foot T8 430 ma Lamp.