If you asked a viticulteur in May/June if they thought this year was going to be a good harvest or not, without tempting fate, they would have said yes as there was plenty of rain in the Spring and a hot, dry summer. However, the recent rains have thwarted progress of the vendange that is already a week later than last year.
The grapes are ripe and ready for picking, but the vendange is not possible in these adverse conditions. If the grapes are picked while they are wet, they will start to rot before they can be processed and this will affect the quality of the wine. However, while they remain on the vines, they become gorged by the rain and there is a danger they will burst before they can be picked which will also have an adverse effect on the taste and quality of the wine.