I am trying to do some analysis and forecasting about a Time Series which is about volumes (how many people call to a call center per hour). I have about 2000 observations, in hourly data. I am aware that there are some gaps between hours (i.e. 3am no one calls).
I'd like to model the level of volume but I am doubting with which model to use. From a preliminar analysis I've done, the ACF of the level has clearly some seasonality. I attach a picture of the level and another of the ACF.
I have been thinking quite hard which model can be appropriate but I'm doubting. I'd thought in a Multiplicative Error Model (MEM), some ARMA-type model or a GARCH-type model. However I am very doubtful which is an interesting approach.
I'd really appreciate any suggestion!