I'm planning to use my miles to upgrade a vacation next summer, but don't know where I'm going yet. I know that upgrade seats become hard to find close to high season for many tourist places (SYD, etc), and was wondering if anyone knows of a list of regions of the world with their corresponding high/low tourist seasons.

Something like:
South Pacific - High (May-June), Low (...)
Western Europe - High (...), Low (...)
...
...

Thanks for any info.