White spots on top of car?

These white spots appeared on the top of my black honda civic. I was thinking oxidation from rail rust but it seems like too big of an area for that. It's pretty darn hot where I live so I was also thinking the top coat could have melted or burnt. Does anyone know what it is and how I can fix it?

Picture:

https://goo.gl/photos/SYEHYqvjTsnghsEf7

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