CEBU, Philippines - A tropical cyclone or "buhawi" is an intense low-pressure system with minimum sustained winds of 35 kilometers per hour (kph). A yearly average of 20 tropical cyclones enter the Philippine Area of Responsibility and 90 percent of these affect the country.
Hazards due to tropical cyclones are strong winds with heavy rainfall that can cause widespread flooding/flashfloods, storm surges, landslides and mudflows.
Classification of tropical cyclones
Tropical cyclones are classified according to their strength and are determined by the speed of the maximum sustained winds near the center.
Tropical depression is from 35 kph to 63 kph; tropical storm is from 64 kph to 117 kph; typhoon is more than 118 kph, while supertyphoon is more than 220 kph.
Structure of a tropical cyclone
The primary components of a tropical cyclone are an eye, a rainband, and an eye wall.
The eye is the center of the tropical cyclones and is normally circular in shape with generally cloud-free skies. The wind is light and calm or there are relatively very light winds and no rain. It ranges in size from 10 to 100 kilometers in diameter.
The eye wall is the ring where very high winds and rains are at the heaviest. The highest winds are on the forward right side of the wall of the storm. If the storm is heading west, the highest winds will be on the northern side of the storm. The heaviest damage occurs when the tropical cyclone's eye wall passes over land.
Raindbands are the spiral bands of showers and thunderstorms surrounding the eye. High wind gusts and heavy downpour often occur in individual rainbands, with relatively calm weather between bands. It covers an area of several square kilometers.
What to do in case of typhoons
•Stay indoors and keep calm.
•Monitor TV and radio reports.
•Secure your home.
•Trim trees near dwellings.
•Keep roads clear of emergency vehicles.
•Go to the nearest designated evacuation center if your house is in a flood-prone area.
•Have a flashlight and radio handy, with fresh batteries. Be warned that cold weather can drain your batteries twice as fast.
•Stock up on food, potable water, kerosene, batteries, and first-aid supplies.
•In case of flooding, turn off the main sources of electricity, gas and water in your home.
•Stack furniture above the expected flood level. Keep appliances, valuables, chemicals, toxic substances, and garbage beyond the reach of floodwaters.
•Avoid low-lying areas, riverbanks, creeks and coastal areas, slopes, cliffs, and foothills. Rain can trigger landslides, rockslides or mudslides.
•Avoid wading through flooded areas. Do not attempt to cross flowing streams.
•Do not operate any electrical equipment during a flood.
•Do not use gas or electrical appliances that have been flooded.
Public Storm Warning Signals
•PSWS#1 Meteorological conditions: A tropical cyclone will affect the locality; winds of 30-60 kph may be expected in at least 36 hours or intermittent rains may be expected within 36 hrs. When the tropical cyclone develops very close to the locality, a shorter lead time of the occurrence of the winds will be specified in the warning bulletin.
•PSWS#1 Impact of the winds: Twigs and branches of small trees may be broken; some banana plants may be tilted or downed; some houses of very light materials (nipa and cogon) may be partially unroofed; unless this warning signal is upgraded during the entire existence of the tropical cyclone, only very light or no damage at all may be sustained by the exposed communities; rice crop, however, may suffer significant damage when it is in its flowering stage.
•PSWS#1 Precautionary measures: When the tropical cyclone is strong or is intensifying and is moving closer, the signal may be upgraded to the next higher level; the waves on coastal waters may gradually develop and become bigger and higher; the people are advised to listen to the latest severe weather bulletin issued by Pagasa every six hours. In the meantime, business may be carried out as usual except when flood occurs; disaster preparedness is activated to alert status.
•PSWS#2 Meteorological conditions: A tropical cyclone will affect the locality; winds of greater than 60 kph and up to 100 kph may be expected in at least 24 hours.
•PSWS#2 Impact of the winds: Some coconut trees may be tilted with few others broken; few big trees may be uprooted; many banana plants may be downed; rice and corn may be adversely affected; large number of nipa and cogon houses may be partially or totally unroofed; some old galvanized iron roofing may be peeled off; in general, the winds may bring light to moderate damage to the exposed communities.
•PSWS#2 Precautionary measures: The sea and coastal waters are dangerous to small seacrafts; special attention should be given to the latest position, the direction and speed of movement and the intensity of the storm as it may intensify and move towards the locality; the general public especially people traveling by sea and air are cautioned to avoid unnecessary risks; outdoor activities of children should be postponed; secure properties before the signal is upgraded; disaster preparedness agencies/organizations are in action to alert their communities.
•PSWS#3 Meteorological conditions: A tropical cyclone will affect the locality; winds of greater than 100 kph up to 185 kph may be expected in at least 18 hours.
•PSWS#3 Impact of the winds: Many coconut trees may be broken or destroyed; almost all banana plants may be downed and a large number of trees may be uprooted; rice and corn crops may suffer heavy losses; majority of all nipa and cogon houses may be unroofed or destroyed and there may be considerable damage to structures of light to medium construction; there may be widespread disruption of electrical power and communication services; in general, moderate to heavy damage may be experienced, particularly in the agricultural and industrial sectors.
•PSWS#3 Precautionary measures: The disturbance is dangerous to the communities threatened/affected; the sea and coastal waters will be dangerous to all seacrafts; travel is very risky especially by sea and air; people are advised to seek shelter in strong buildings, evacuate low-lying areas and to stay away from the coasts and river banks; watch out for the passage of the 'eye' of the typhoon indicated by a sudden occurrence of fair weather immediately after very bad weather with very strong winds coming generally from the north; when the 'eye' of the typhoon hit the community do not venture away from the safe shelter because after one to two hours the worst weather will resume with the very strong winds coming from the south; classes in all levels should be suspended and children should stay in the safety of strong buildings; disaster preparedness and response agencies/organizations are in action with appropriate response to actual emergency.
•PSWS# 4 Meteorological conditions: A very intense typhoon will affect the locality; very strong winds of more than 185 kph may be expected in at least 12 hours.
•PSWS#4 Impact of the winds: Coconut plantation may suffer extensive damage; many large trees may be uprooted; rice and corn plantation may suffer severe losses; most residential and institutional buildings of mixed construction may be severely damaged; electrical power distribution and communication services may be severely disrupted; in the overall, damage to affected communities can be very heavy.
•PSWS#4 Precautionary measures: The situation is potentially very destructive to the community; all travels and outdoor activities should be cancelled; evacuation to safer shelters should have been completed since it may be too late under this situation; with PSWS #4 the locality is very likely to be hit directly by the eye of the typhoon. As the eye of the typhoon approaches, the weather will continuously worsen with the winds increasing to its strongest coming generally from the north. Then a sudden improvement of the weather with light winds (a lull) will be experienced (ironically, the eye is the weakest part of a typhoon). This means that the eye of the typhoon is over the locality. This improved weather may last for one to two hours depending on the diameter of the eye and the speed of movement. As the eye moves out of the locality, the worst weather experienced before the lull will suddenly commence. This time the very strong winds will come generally from the south. The disaster coordinating councils concerned and other disaster response organizations are now fully responding to emergencies and in full readiness to immediately respond to possible calamity.
Source: "Disaster Preparedness & First Aid Handbook" prepared by the Senate Committee on Climate Change in coordination with the Philippine Institute of Volcanology and Seismology, National Disaster Risk Reduction and Management Council, Department of Education, Department of Health; Philippine Atmospheric, Geophysical and Astronomical Services Administration, Bureau of Fire Proteciton, Mines and Geosciences Bureau, and Vigan City Disaster Risk Reduction and Management Council