I am attempting to establish periodicity within my data set that includes 2 cycles for each month of the year. So for example, year 1(2015), month 1 (January) has two cycles, month 2 (February) has two cycles, month 3 (March) has two cycles and so forth. Each year would have 24 observations (two cycles per month). Is there a way to handle such periodicity where time series forecasting can be appropriately utilized? I’m currently running SPSS version 24. I developed a workaround by rolling things up to only month and year, but I’m a little concerned the seasonal effects will not be modeled accurately.