An engine running when the ambient temp is high usually can't use as much boost as one running in cool weather. But if you didn't change anything, the boost shouldn't change from one day to the next. The waste gate actuator is working off the differential pressure between the atmosphere and the turbo discharge. That means the waste gate will open, lowering boost, without much change, if any, due to temp. The knock sensor and the ECM may be shutting off the wastegate solenoid, though, and decreasing boost. Some of the chip gurus will have to answer that- I can't remember is there's a temperature input to the tables that control the wastegate solenoid. If you run "tuner style", and take the waste gate solenoid out of the picture, then boost should stay about the same, regardless of ambient temp. Or that's what I think, anyway.