Sunday, February 6, 2011

Tropical Cyclones

Tropical Cyclone Yasi hit Queensland, Australia a few days ago, causing millions of dollars in damages.  The silver lining in this unfortunate episode, is that it missed areas of concentrated populations. It is worth noting that the sheer size of the weather system would have wreaked much more havoc had it hit elsewhere.  

What is a Tropical Cyclone
A tropical cyclone is essentially a spiraling mass of wet air centred around an area of low atmospheric pressure most commonly known as the "eye". On the ocean, a cyclone is continually fed as evaporated water from the ocean surface condenses, releasing more heat as the air current rises. Owing to the Coriolis effect, a cyclone spins counterclockwise in the Northern Hemisphere and clockwise in the Souther Hemisphere.

Strength Categories
According to the Saffir-Simpson Hurricane Scale, Yasi was a category 5 cyclone, the strongest of its kind. It reached wind speeds of 250km/h, and storm surges of greater than 18ft.

Category
Wind Speed mph
(km/h)
Storm Surge ft
(m)
Five
≥ 156
(≥ 250)
> 18
(> 5.5)
Four
131–155
(210–249)
13–18
(4.0–5.5)
Three
111–130
(178–209)
9–12
(2.7–3.7)
Two
96–110
(154–177)
6–8
(1.8–2.4)
One
74–95
(119–153)
4–5
(1.2–1.5)

Hurricanes and Typhoons
Cyclones are more commonly known as hurricanes in the North Atlantic and the Northeast Pacific. The word hurricane maybe derived from the Mayan storm god, Huracan. In the Northwest Pacific and east Asia, cyclones are called typhoons. This word may have originated from the Greek mythological monster, Typhon, often associated with storms. The phonetics behind the word typhoon translates well into "strong winds" in Chinese and Japanese. Hence, it is also used in these regions.

Naming Conventions
Meteorology centres throughout the world have their own naming conventions for cyclones, hurricanes and typhoons.  In most areas, a set of female names in alphabetical order is often pre-assigned before the season to name these natural phenomena. In Australia, cyclone names have alternated between male and female names since 1976. Cyclones are sometimes renamed when it moves from one region to another. Names are also recycled every few years, but devastating storm names like Hurricane Katrina of 2005 are usually retired to note historic significance.


-PTS

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