How do you determine typhoon signals?

Answer 1

THE PHILIPPINE 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 hours. (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.)

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.

PRECAUTIONARY MEASURES:

• When the tropical cyclone is strong or is intensifying and is moving closer, this 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 occur.
• Disaster preparedness is activated to alert status.

PSWS # 2

METEOROLOGICAL CONDITIONS:

• A tropical cyclone will affect the the locality.
• Winds of greater than 60 kph and up to 100 kph may be expected in at least 24 hours.

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 roofings may be peeled off.
• In general, the winds may bring light to moderate damage to the exposed communities.

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 travelling 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.

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.

PRECAUTIONARY MEASURES:

• The disturbance is dangerous to the communities threatened/affected.
• The sea and coastal waters will be very 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 gnerally 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.

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.

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. 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.

FOOTNOTES: Important to note that when any Public Storm Warning Signal Number is hoisted or put in effect for the first time, the corresponding meteorological conditions are not yet prevailing over the locality. This is because the purpose of the signal is to warn the impending occurrence of the given meteorological conditions. It must be noted also that the approximate lead time to expect the range of the wind speeds given for each signal number is valid only when the signal number is put in effect for the first time. Thus, the associated meteorological conditions are still expected in at least 36 hours when PSWS #1 is put in effect initially; in at least 24 hours with PSWS #2; in at least 18 hours with PSWS #3; and in at least 12 hours with PSWS #4. The lead time shortens correspondingly in the subsequent issues of the warning bulletin when the signal number remains in effect as the tropical cyclone comes closer.

It is also important to remember that tropical cyclones are constantly in motion; generally towards the Philippines when PAGASA is issuing the warning. Therefore, the Public Storm Warning Signal Number over a threatened/ affected locality may be sequentially upgraded or downgraded. This means that PSWS #1 may be be upgraded to PSWS #2, then to PSWS #3 and to PSWS #4 as necessary when a very intense typhoon is approaching or downgraded when the typhoon is moving away. However, in case of rapid improvement of the weather condition due to the considerable weakening or acceleration of speed of movement of the tropical cyclone moving away from the country, the downgrading of signal may jump one signal level. For example, PSWS #3 may be downgraded to PSWS #1 or all signals from PSWS #2 may be lowered.

The delineation of areas for a given signal number is based on the intensity, size of circulation and the forecast direction and speed of movement of the tropical storm or typhoon at the time of issue of the warning bulletin. The change in intensity, size of circulation or movement of the tropical cyclone also determines the change in the PSWS number over a given locality.

Answer 2

Typhoon signals are determined by analyzing the strength and location of a typhoon, as well as its potential impact on the affected area. Meteorological agencies use various criteria, such as wind speed and direction, to issue signals that indicate the level of threat posed by the typhoon. These signals help authorities and residents prepare and take necessary precautions.