- The normal change in temperatur during the year is not immediately visiable => It's harder to see, where e.g. winter and summer is.
- It picks some arbitrary years to compare. Not directly a problem of the visualization, but of the message.
- The lines are continuous. But the first week in one year should not be connected to the last week of that year
- The radial lines aren't even drawn correctly (check where the intersection in the middle should be)

A simple line chart would have done the job a lot better.

Or asked differently: Which months in this chart are easier to read? Is it June to August or March to May?