Owm gives hourly predictions in 3-hour-intervals: For 17:00, 20:00, 23:00, and so on.
Possible solutions:
just leave 18:00, 19:00, 21:00, ... out
fill in the gaps with the same values from before, e.g. the values from 17:00 for 18:00 and 19:00, or the values from 17:00 for 18:00 and the values from 20:00 for 19:00
interpolate linearly, e.g. for 18:00 and 19:00 take the respective weighted average of 17:00 and 20:00
Owm gives hourly predictions in 3-hour-intervals: For 17:00, 20:00, 23:00, and so on. Possible solutions: