A typhoon refers to a tropical cyclone that
originates in the China Sea. They have steep
pressure gradient and are most frequent
between July and October.
3. The same storm may be
considered a typhoon in one
region of the ocean and a
hurricane in another region. In the
Northern Hemisphere it rotates in
anticlockwise direction and in
clockwise direction in the Southern
4. A typhoon usually follows three different
directions: straight, recurving and northward. A
straight path is defined as a westward path; the
storm will head toward the Philippines, the south
of China, Taiwan and Vietnam. A storm that
follows a recurving path will head towards the
east of China, Taiwan, Korea and Japan. A
northward path occurs when the storm simply
heads north of its point of origin. This will affect
small islands throughout the Pacific Ocean.
5. (a)The surface winds blow inward in a counter clockwise direction toward
(b)The tropical cyclone may show no cooling, or very little, toward the
(c) In mature tropical cyclones, almost all the cloud forms are present, but
by and large the most significant clouds are the heavy cumulus and
cumulonimbus which spiral inward toward the outer edge of the eye.
tropical cyclone may show no cooling, or very little, toward the storm
(d) The eye’s diameter averages about 15 miles, but it may attain 40 miles in
large typhoons. The eye is constantly undergoing transformation and does
not stay in a steady state.
(e) The winds of a tropical cyclone produce wind waves which move
outward from its center.
(f)There will be high precipitation
Internationally if any storm is having a speed of more than
65 knots is called a typhoon.
(b)Severe typhoon ----150-184km/hr
(c)Super typhoon------185km/hr or above.
Saffir Simpson Hurricane Wind Scale gives 6 categories.
Category 6 ----156 knots
Category 5 ---- 137knots
Category 4 ----113-136knots
Category 3 ---- 96-112knots
Category 2 ----83-95knots
Category 1 ----64-82knots
Tropical cyclones form only over warm ocean waters near the equator.
To form a cyclone, warm,moist air over the ocean rises upward from
near the surface. As this air moves up and away from the ocean surface,
it leaves less air near the surface. So basically as the warm air rises, it
causes an area of low air pressure below. Air from surrounding areas
with higher pressure pushes in to the low pressure area. Then this new
cool air becomes warm and moist and rises, too. And the cyclone
continues. As the warmed, moist air rises and cools the water in the air
forms clouds and wind spins and grows, fed by the ocean’s heat and
water evaporates from the ocean surface. As the storm system rotates
faster and faster, a eye forms in the centre. It is very calm and clear in
the eye, with very low air pressure. Higher pressure air from above flows
down into eyes.
12. Historic Typhoons
(a)Typhoon Nancy in 1961, Northwest Pacific
(b)Bhola Cyclone in 1970, Bangladesh.
(c)Typhoon Nina in 1975, China.
(d)Hurricane Katrina in 2005, United States.
(e)Cyclone Yasi in 2011, Australia.
Cyclone create several dangers for people around tropical
areas . The most destructive force of a cyclone comes
from the fierce winds.
(a)These winds easily topple fences, sheds, trees, power
poles and caravans, while hurling helpless people through
(b)Many people are killed when the cyclone winds cause
buildings to collapse and houses to completely blow away .
(c)It causes high rainfall which leads to flooding and
14. Forecast of Typhoons
Satellite and radar technology is used for
forecasting the typhoons. Surface charts are
analysed on hourly basis to provide information
on position, direction and intensity. The science
of tropical cyclone forecasting is by no means
perfect. The volatile nature of tropical cyclones,
with their inherent fluctuation in both motion
and intensity, is also partly to blame for this.
15. Disaster Management
Typhoon is a natural disaster so it is difficult to prevent it
but we can reduce the scale of destruction by taking
If we decide to take shelter at home:
•Turn off all electricity, gas and water and unplug all
•Keep your Emergency Kit close at hand
•Bring your family into the strongest part of the house
•Keep listening to the radio for cyclone updates and
remain indoors until advised.
We must stay inside unless it is officially declared safe to
16. The time immediately after a cyclone is often just as
dangerous as the initial event itself. Once we have been
advised that the typhoon has passed, we must adhere to
•Listen to our radio and remain indoors until advised.
•If we are told to return to our home, we must do so
using the recommended routes only.
•We should not use electrical appliances which have been
wet until they are checked for safety.