vectors - Determine the number of days with North-East wind direction from the number of days with North and East wind direction?

I have some data like:

Wind flow from north direction = “X” Numbers of days.

Wind flow from east direction = “Y” Numbers of days.

Then is there any formula to know numbers of days wind flows from North-East direction?

Answer

Generally speaking there will be some correlation between wind directions. For example if on some specific day the wind blows from the North or East it is quite likely there was a North-East wind in the week or so around that day. By contrast if the wind is from the South-West on a particular day it is less likely there was a North-East wind in the week or so around that day.

However these are statistical correlations. If you measure wind directions over many days and analyse your data you'll find this type of correlation. The degree of correlation will vary with location and season, and possibly other variables I haven't thought of. So there is no answer to your question unless you make it more precise.