Hi keltic
The ITCZ can be considered as the thermal ecuator.
Depending on the season and also monsoon effects, the ITCZ shifts north or south, but if you are in the ITCZ it doesn't matter what is the season. You are in it, and that's what matters.
If you have to fly from A to B and the ITCZ is in the middle, you have to cross it whether you like it or not. That's the problem. From South America to Europe, that is the case.