I am not very convinced by the forecasting abilities of the Prophet package. In the sample provided, it looks to me as if the data is overfitted. Prophet might pick the yearly cycle correctly but I am uncertain about the weekly pattern it finds. Essentially this pattern leads to negative values in the forecasting period which seems incorrect to me. I understand that the main purpose of this post is to demonstrate the easy use of the software package. However, I would have appreciated if the forecast could have been evaluated properly on a hold-out sample against some simple benchmarks such as a seasonal Naive. Otherwise, I think it is risky to say that “Prophet did an excellent job on the time series”.