Objectives:
After performing this activity, you should be able to:
1. explain what two weather factors tell weathermen that a certain location is at the eye of a tropical cyclone; and
2. put in simple words the statement “calm before the storm.”
Materials Needed:
weather data (air pressure and wind speed)
Procedure:
1. Figure 1 consists of two illustrations. The top one shows a tropical cyclone as seen at an angle. White rain bands move around the center or “eye”. The bottom illustration shows a cross-section of a tropical cyclone. It is like slicing it in half and looking at it from the side.
Figure 4. (Top) View of a tropical cyclone at an angle.
(Bottom) Cross-section of a typhoon.
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Q7. Location A is within the eye of the tropical cyclone. B, C and D are locations that are more and more distant from the eye. The air pressure at the different locations are:
Location A B C D
Air pressure
*
in millibars (mb) 930 960 980 990
*Air pressure refers to the weight of air over a certain area.
Compare the air pressures at A, B, C and D. What do you notice?
Q8. Location E is within the eye of the tropical cyclone. Location F is within the clouds surrounding the eye. The clouds at F make up the eyewall. The wind speed at the two locations are:
Location E F
Wind speed (km/hour) 10 200
Compare the wind speed within the eye and at the eyewall. What can you say?
As you have learned from the activity, the lowest air pressure is at the eye of a tropical cyclone. In fact, all tropical cyclones have low air pressure at the center.
This is the reason why the air in the surroundings move toward the eye. Recall in Grade 7 that air moves toward low-pressure areas.
You also learned that at the eye of a tropical cyclone, wind speed is low. But in the dense clouds surrounding the eye, at the eyewall itself, the wind speed is great. When newspapers report that a tropical cyclone has sustained winds of 200 km/hour, for instance, they are referring to the winds at the eyewall.
When the eye of a tropical cyclone passes over a certain place, it is the winds at the eyewall that wreak a lot of damage. As it approaches, one side of the eyewall brings strong winds blowing in one direction. Then comes the eye with its somewhat calm weather. As it leaves, the other side of the eyewall brings strong winds again, but this time in the opposite direction.
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Are You Prepared?
When a tropical cyclone enters the PAR and it is on its way toward land, warning signals are issued. The following signals are used by PAGASA to warn people about the approaching weather disturbance. Do you know what the signals mean?
PUBLIC STORM WARNING SIGNALS (PSWS)
PSWS # 1
What it means
A tropical cyclone will affect the locality
Winds of 30-60 kph may be expected in at least 36 hours or irregular rains may be expected within 36 hours
The following may happen
Twigs and branches of small trees are broken Some banana plants are tilted or downed
Some houses of very light materials partially unroofed Rice crops suffer significant damage in its flowering stage
What to do
Watch out for big waves
Listen to severe weather bulletin issued by PAGASA
150 PSWS # 2
What it means
A tropical cyclone will affect the locality
Winds of greater than 60 kph up to 100 kph may be expected in at least 24 hours
The following may happen
Large number of nipa and cogon houses may be partially or totally unroofed Some old galvanized iron roof may be peeled off
Winds may bring light to moderate damage to exposed communities Some coconut trees may be tilted while few are broken
Few big trees may be uprooted Many banana plants may be downed Rice and corn may be adversely affected What to do
Avoid riding in small seacraft
Those who travel by sea and air should avoid unnecessary risks Postpone outdoor activities of children
PSWS # 3
What it means
A tropical cyclone will affect locality
Winds of greater than 100 kph to 185 kph may be expected in at least 18 hours
The following may happen
Many coconut trees broken or destroyed
Almost all banana plants downed and a large number of trees uprooted Rice and corn crops suffer heavy losses
Majority of all nipa and cogon houses uprooted or destroyed; considerable damage to structures of light to medium construction
Widespread disruption of electrical power and communication services Moderate to heavy damage experienced in agricultural and indistrial sectors
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Avoid riding in any seacraft Seek shelter in strong buildings Evacuate from low-lying areas
Stay away from coasts and river banks
PSWS # 4 What it means
A very intense typhoon will affect locality
very strong winds of more than 185 kph maybe expected in at least 12 hours
The following may happen
Coconut plantation may suffer extensive damage Many large trees maybe uprooted
Rice and corn plantation may suffer severe losses
Most residential and institutional buildings of mixed construction maybe severely damaged
Electrical power distribution and communication services maybe severely disrupted
Damage to affected communities ca be very heavy
What to do
All travels and outdoor activities should be cancelled
Evacuation to safer shelters should have been completed by now The locality is very likely to be hit directly by the eye of the typhoon.
To be fully prepared for tropical cyclones, you should also put together an emergency kit which includes the following: drinking water, canned goods, can opener, radio, flashlight, extra batteries, clothes, blanket, and first aid kit. You never know when you will need it. You must learn how to rely on yourself. In times of disaster, it may take a while before help arrives.
152 References and Links
Tarbuck, E.J., & Lutgens, F.K. (2004). Earth Science (10th ed.). First Lok Yang Road, Singapore: Pearson Education (Asia) Pte Ltd.
http://www.pagasa.dost.gov.ph/
http://www.ready.gov/hurricanes
http://www.noaawatch.gov/themes/tropical.php
http://weather.unisys.com/hurricane/w_pacific/2011H/index.php http://en.wikipedia.org/wiki/Tropical_Storm_Washi
http://people.cas.sc.edu/carbone/modules/mods4car/tropcycl/index.html
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