The festival of the start of the harvest, at the beginning of August, is associated with the concepts of sacrifice and sudden change. The grain must be cut down to be turned into food as part of the cycle of life. However, The Blasted Oak isn't about planned gathering of crops, it is about unexpected calamity. In the picture on the card a man falls from the branch of a tree that's been struck by lightning.
The card isn't so much predicting a disaster as showing the forces of nature destroying unsafe structures we might have clung to. In this case, the branch was probably already rotten. That might symbolise a flawed ideology or belief we need to move away from, it might represent an emotional attachment that wasn't helping us, or it might symbolise something material that was only offering false security. It is time for those things to end. If we do not choose to let them go, we might take a tumble when they give way naturally.
Do not be angry if something happens that strips away your illusions. It is possible to learn from the experience, even if one is burnt by the lightning strike of sudden realisation or bruised from the fall. Allow yourself time to recover, be patient, and be wiser in future.
Links to previous readings for the world: