if you have daily missing data and you need a full time-series, you can use linear interpolation to fill the missing data gaps. However, I am not sure I fully understand what you mean by "extracting the maximum daily rainfall from the average monthly rainfall ". Is the average monthly rainfall data are average of maximum daily rainfall values? Also maximum per hour? or maximum daily rainfall in a month?
I work on a project where I have to use the maximum daily rainfall, but I only have the monthly rainfall as data, can I find a relationship between the two parameters
Use data from hyetograph to plot a mass curve (Rainfall depth vs Time (days) where you plot the data for every 30 days and eventually estimate the missing daily catch on your mass curve.