Buys Ballot's Law - Uses

Uses

The law outlines general rules of conduct for masters of both sail and steam vessels, to assist them in steering the vessels away from the center and right front (in the Northern Hemisphere and left front in the Southern Hemisphere) quadrants of hurricanes or any other rotating disturbance at sea. Note that prior to radio, satellite observation and the ability to transmit timely weather information over long distances, the only method a ships master had at his disposal to forecast the weather was observation of meteorological conditions (visible cloud formations, wind direction and atmospheric pressure) at his location.

Included in the "Sailing Directions for the World" are Buys Ballot's Law techniques for avoiding the worst part of any rotating storm system at sea using only locally observable phenomena i.e. cloud formations, wind speed and barometric pressure tendencies over a number of hours. These observations and application of the principles of Buys Ballot's Law help to establish the probability of the existence of a storm and the best course to steer to try avoid the worst of it—with the best chance of survival.

From a slightly less esoteric standpoint the underlying principles of Buys Ballot's Law states that for anyone ashore in the Northern Hemisphere and in the path of a hurricane, the most dangerous place to be is in the right front quadrant of the storm. There, the observed wind speed of the storm is the sum of the speed of wind in the storm circulation plus the velocity of the storms forward movement. Buys Ballot's Law calls this the Dangerous Quadrant. Likewise, in the left front quadrant of the storm the observed wind is the difference between the storm's wind velocity and its forward speed. This is somewhat euphemistically called the Safe Quadrant due to the lower observed wind speeds.

To look at it another way, in the Northern Hemisphere if a person is to the right of where a hurricane or tropical storm makes landfall, that is considered the dangerous quadrant. If they are to the left of the point of landfall, that is the safe quadrant. In the dangerous quadrant an observer will experience higher wind speeds and generally a much higher storm surge due to the wind direction (onshore). In the Safe quadrant, the observer will experience somewhat lower wind speeds and the possibility of lower than normal water levels due to the direction of the wind being offshore.

These are very general rules that are subject to many other factors, e.g. shapes of the coastline, and topography in any location. Although the principles here to a very limited extent apply to a coastal observer during the approach and passage of a storm in any location, Buys Ballot's Law was primarily formulated from empirical data to assist ships at sea.