Re: Wind direction is measured in 0 to 540 degrees, why?

Actually, wind direction is measured in tens of degrees ranging from 10 to 
360 where 360 represents north, 90 degrees represents east, 180 degrees 
south and 270 degrees represents west.  This convention for determining 
wind direction is tied to aviation which uses the same compass points to 
determine heading information.  Since a plane in flight will be affected by 
the wind as it flies through the air, it is necessary for winds and planes 
to refer to the same compass to accurately determine the aircraft's 
heading.

The wind direction represents the direction from which the wind is blowing. 
For example, when the wind is 220 degrees (or southwest), the wind is 
blowing from the southwest toward the northeast. For meteorologists, it is 
important for us to know from where the wind is blowing since we attempting 
to forecast the weather.  In forecasting, we are trying to predict what 
weather is headed our way rather than what weather is moving away from us. 
In the a simplified case, if it is raining 20 kilometers to the west of 
us and the wind at cloud level is westerly at 20 kilometers per hour, then 
it will rain on us in about an hour.  

More importantly though, the wind direction aids us by helping us determine 
the characteristics of the air headed in our direction.  For example, a 
southeast wind across the Arabian Sea would tend to make it more humid 
in Bahrain and could result in rain over the area.  A northwest flow across 
the Arabian Peninsula would tend to be a drier flow for your area.