Back to Back Issues Page
Blowin' in the Wind, Issue #041 The requisite meteorology conditions for a typhoon - March 29, 2007
March 28, 2007
Hello ,

Find the right meteorology conditions for a typhoon.

Hello down under! As your season wraps up, we have some meteorology conditions for a typhoon in case you wondered. Now you can make sense of those typhoon warnings. And these principles apply to hurricanes as well.

Different words for the same thing come from different places. This one, typhoon, apparently comes from the word "taaifung" from the Chinese language of Cantonese, with older, Arabic / Indian versions such as "touffon". All of these words meant wind (of some sort, e.g. whirlwind). "Typhoon" took on its modern spelling in English in the early 1800's.

So where do they call it a typhoon? When it occurs in the western half of the Pacific ocean, around Asia and Oceania. Similar storms in the Indian ocean get called typhoons as well.

Tropical cyclones can occur anywhere in the tropics, although they seem to prefer certain locales.

Wannabe Hurricanes:

We have a couple of little sisters. Tropical storms and tropical depressions fail to provide winds that exceed that magical 75 mph (120 km/h) threshold that separate them from the big boys.

What happens inside?

Think of it as a giant turbine. The engine operates under the energy released by the transformation of its fuel. In the case of the typhoon or hurricane (they're really the same thing), that fuel is water vapour and the heat released is the latent heat given off when that water vapour condenses into liquid and becomes rain. That heat is enormous. That's what drives the wind.

The storm's main function is to transport excess heat from the equatorial regions towards the poles, and water vapor is an efficient way of carrying the heat. However, the storm needs sufficient heat and moisture to get started. How much, you ask? Exactly how do they form? Nobody knows it all yet but it can't fire up without these things, the requisite meteorology conditions for a typhoon:

  1. Water temperature of 26.5°C (80°F)
  2. water temperature of 26.5° to a minimum depth of 50m (164 ft)
  3. instability (air that suddenly becomes cooler a short distance above the surface)
  4. high relative humidity in this air, further contributing to the instability
  5. gentle winds, without any shear to rip the structure apart
  6. sufficient Coriolis force to create circular flow. This force is automatically available in sufficient strength at distances greater than 5° (about 335 miles or 555 km) North or South of the equator.
  7. A small storm to use as a seed for the big one.

Throw all those ingredients in a box and you got a typhoon, right? Well, not exactly. Many opportunities for hurricane storms to form slip by every year without becoming one. That's the thing meteorologists have not quite put a finger on yet. The missing meteorology conditions for a typhoon. Read more about these magnificant storms right here.

...and see some great photos too.

Back to Back Issues Page