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Posted by Michael V. Padua (Webadmin) on November 23, 2010, 6:41 pm, in reply to "Re: Weather enthusiasts"
Board Administrator
@ Richard:
This is taken from my TC 101 slide lectures that I do here in Naga and elsewhere:
Buys Ballot’s Law (Wind Shifting)
Buys Ballot's Law - This is a law describing the relationship of the horizontal wind direction in the atmosphere to the pressure distribution. "If one stands facing the wind in the Northern Hemisphere, the storm will always be to the right." "In the Southern Hemisphere, if one stands facing the wind, the storm will always be to the left."
This law was first formulated in 1857 by the Dutch meteorologist, Buys Ballot, and bears his name. It is also known as the Baric Wind Law.
FIRST or INITIAL WIND - The initial tropical cyclone winds as observed on the surface blowing from the North, NE or NW. This means that the tropical cyclone is approaching.
SECOND or FINAL WIND - The final tropical cyclone winds as observed on the surface from SW, South or SE. This means that the tropical cyclone is now leaving or just starting to leave the area.
VEERING - refers to the shifting of the wind direction of a tropical cyclone observed by the observer from North/NE thru SE by way of East. It also means that the tropical cyclone is passing South of the observed place.
BACKING - refers to the shifting of the wind direction of a tropical cyclone observed by the observer from North/NW thru SW by way of West. It also means that the tropical cyclone is passing North of the observed place.
A rule of thumb: In the Northern Hemisphere, a location can expect winds coming from the North, this is simply because Typhoons forms East or SE of the Philippines and move towards either West or WNW. If the wind you feel changes:
From North, from NE, from East, from SE, & finally from South) >> the Eye is passing SOUTH of you…Or;
From North, from NW, from West, from SW, & finally from South) >> the Eye is passing NORTH of you.
If it remains steady from the North/NE (if the storm comes from the SE/ESE of your location, moving on a WNW track) or from the North/NW (if the storm comes the NE/ENE of your location, moving on a WSW track) --> expect the Eye to pass over your location in which a sudden lull can be expected.
The duration of the lull depends on how large or small the Eye is or on how slow or fast the typhoon moves. Some lull can last for 5 mins. (eg. Hurricane Charley) while others up to 6 hours (especially an Eye with more than 100 km. in diameter). Avg. lull is 30 mins to 1 or 2 hours.
After the lull, the back side of the typhoon can be expected and this time the damaging winds will be coming from South/SW or South/SE.
I HOPE THIS WILL HELP. 
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