It's a tricky one because there is no negligence by ASDA. You could argue that you should have spotted this, and being aware of the weather conditions, expected something like this could happen. As such, you should have parked elsewhere. If it was not parked where it was, it would not have been damaged. The flip side of this is, the supermarket has a duty of care to prevent damage or injury to others whilst on their property. Are there signs that read something like 'park at your own risk'? A gust of wind would be seen as an Act of God. I would contact ASDA and request their public liability insurance details. They will not want to provide this, as they will have a high excess, and will be technically self-insuring. You may well find this tactic will assist you in having them compensate you for the damage. I would not expect success, but there's no harm in trying.