typhoons in the philippines

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Typhoons in the Philippines

Typhoons in the Philippines

OVERVIEWIn the Philippines, tropical cyclones (typhoons) are called bagyo. Tropical cyclones entering the Philippine area of responsibility are given a local name by the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA), which also raises public storm signal warnings as deemed necessary.

Around 19 tropical cyclones or storms enter the Philippine Area Of Responsibility in a typical year and of these usually 6 to 9 make landfall.

Why Bagyo?The term bagyo, a Filipino word meaning typhoon arose after a 1911 storm in the city of Baguio had a record rainfall of 46inches within a 24-hour period.

Variability in ActivityOn an annual time scale, activity reaches a minimum in May, before increasing steadily through June, and spiking from July through September, with August being the most active month for tropical cyclones in the Philippines. Activity falls off significantly in October.

The most active season, since 1945, for tropical cyclone strikes on the island archipelago was 1993 when nineteen tropical cyclones moved through the country (though there were 36 storms that were named by PAGASA). There was only one tropical cyclone which moved through the Philippines in 1958.

The most frequently impacted areas of the Philippines by tropical cyclones are northern Luzon and eastern Visayas. A ten year average of satellite determined precipitation showed that at least 30percent of the annual rainfall in the northern Philippines could be traced to tropical cyclones, while the southern islands receive less than 10percent of their annual rainfall from tropical cyclones.

Public Storm Warnings and Signals

The Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) releases tropical cyclone warnings in the form of Public Storm Warning Signals. An area having a storm signal may be under:

PSWS #1 - Tropical cyclone winds of 30km/h (19mph) to 60km/h (37mph) are expected within the next 36hours. (Note: If a tropical cyclone forms very close to the area, then a shorter lead time is seen on the warning bulletin.)

PSWS #1 - Tropical cyclone winds of 30km/h (19mph) to 60km/h (37mph) are expected within the next 36hours. (Note: If a tropical cyclone forms very close to the area, then a shorter lead time is seen on the warning bulletin.)

PSWS #2 - Tropical cyclone winds of 60km/h (37mph) to 100km/h (62mph) are expected within the next 24hours.

PSWS #3 - Tropical cyclone winds of 100km/h (62mph) to 185km/h (115mph) are expected within the next 18hours.

PSWS #4 - Tropical cyclone winds of greater than 185km/h (115mph) are expected within 12hours.

Anatomy of a Typhoon

Eye At this part, the Weather has no rain but sunny sky.Inner Bands The rain is harder and the wind is weaker. Outer Bands The rain is weaker but the wind is stronger.Edge both winds and rains has the same power.


Worldwide, tropical cyclone activity peaks in late summer, when the difference between temperatures aloft and sea surface temperatures is the greatest. However, each particular basin has its own seasonal patterns. On a worldwide scale, May is the least active month, while September is the most active month. November is the only month in which all the tropical cyclone basins are active.

LocationsMost tropical cyclones form in a worldwide band of thunderstorm activity near the equator, referred to as the Intertropical Front (ITF), the Intertropical Convergence Zone (ITCZ), or the monsoon trough. Another important source of atmospheric instability is found in tropical waves, which contribute to the development of about 85% of intense tropical cyclones in the Atlantic ocean and become most of the tropical cyclones in the Eastern Pacific.

The majority forms between 10 and 30degrees of latitude away of the equator, and 87% forms no farther away than 20degrees north or south. Because the Coriolis effect initiates and maintains their rotation, tropical cyclones rarely form or move within 5degrees of the equator, where the effect is weakest. However, it is still possible for tropical systems to form within this boundary

Movements and Tracks

PathsMost tropical cyclones form on the side of the subtropical ridge closer to the equator, then move poleward past the ridge axis before recurving north and northeast into the main belt of the Westerlies. When the subtropical ridge position shifts due to El Nio, so will the preferred tropical cyclone tracks. Areas west of Japan and Korea tend to experience much fewer SeptemberNovember tropical cyclone impacts during El Nio and neutral years.

During El Nio years, the break in the subtropical ridge tends to lie near 130E which would favor the Japanese archipelago. During La Nia years, the formation of tropical cyclones, along with the subtropical ridge position, shifts westward across the western Pacific ocean, which increases the landfall threat to China and greater intensity to Philippines.

Typhoon paths follow three general directions.Straight track (or straight runner). A general westward path affects the Philippines, southern China, Taiwan, and Vietnam.A parabolic, recurving track Storms recurving affect eastern Philippines, eastern China, Taiwan, Korea, and Japan.Northward track. From point of origin, the storm follows a northerly direction, only affecting small islands.

Coriolis EffectThe Earth's rotation imparts an acceleration known as the Coriolis effect, Coriolis acceleration, or colloquially, Coriolis force. This acceleration causes cyclonic systems to turn towards the poles in the absence of strong steering currents. The poleward portion of a tropical cyclone contains easterly winds, and the Coriolis effect pulls them slightly more poleward.

The westerly winds on the equatorward portion of the cyclone pull slightly towards the equator, but, because the Coriolis effect weakens toward the equator, the net drag on the cyclone is poleward. Thus, tropical cyclones in the Northern Hemisphere usually turn north (before being blown east), and tropical cyclones in the Southern Hemisphere usually turn south (before being blown east) when no other effects counteract the Coriolis effect.

LandfallOfficially, landfall is when a storm's center (the center of its circulation, not its edge) crosses the coastline. Storm conditions may be experienced on the coast and inland hours before landfall; in fact, a tropical cyclone can launch its strongest winds over land, yet not make landfall; if this occurs, then it is said that the storm made a direct hit on the coast.

Fujiwara EffectWhen two cyclones approach one another, their centers will begin orbiting cyclonically about a point between the two systems. The two vortices will be attracted to each other, and eventually spiral into the center point and merge. When the two vortices are of unequal size, the larger vortex will tend to dominate the interaction, and the smaller vortex will orbit around it. This phenomenon is called the Fujiwhara effect

DissipitationA tropical cyclone can cease to have tropical characteristics in several different ways. One such way is if it moves over land, thus depriving it of the warm water it needs to power itself, quickly losing strength. Most strong storms lose their strength very rapidly after landfall and become disorganized areas of low pressure within a day or two, or evolve into extratropical cyclones. There is a chance a tropical cyclone could regenerate if it managed to get back over open warm water.

ClassificationTropical cyclones are classified into three main groups, based on intensity: tropical depressions, tropical storms, and a third group of more intense storms, whose name depends on the region.

A tropical depression is an organized system of clouds and thunderstorms with a defined, closed surface circulation and maximum sustained winds of less than 34 knots (39mph). It has no eye and does not typically have the organization or the spiral shape of more powerful storms. However, it is already a low-pressure system, hence the name "depression" In the Philippines, the practice is to name tropical depressions from their own naming convention when the depressions are within the country's area of responsibility.

A tropical storm is an organized system of strong thunderstorms with a defined surface circulation and maximum sustained winds between 34 knots (39mph) and 64 knots (74mph). At this point, the distinctive cyclonic shape starts to develop, although an eye is not usually present. Government weather services first assign names to systems that reach this intensity (thus the term named storm).

A hurricane or typhoon (sometimes simply referred to as a tropical cyclone, as opposed to a depression or storm) is a system with sustained winds of at least 34 metres per second (66kn) or 74 miles per hour (119km/h).A cyclone of this intensity tends to develop an eye, an area of relative calm (and lowest atmospheric pressure) at the center of circulation. The eye is often visible in satellite images as a small, circular, cloud-free spot.

Surrounding the eye is the eyewall, an area about 16 kilometres (9.9mi) to 80 kilometres (50mi) wide in which the strongest thunderstorms and winds circulate around the storm's center. Maximum sustained winds in the strongest tropical cyclones have been estimated at about 85 metres per second (165kn) or 195 miles per hour (314km/h).

Name SourcesThe list of names consists of entries from 17 East Asian nations and the United States who have territories directly affected by typhoons. The submitted names are arranged into five lists; and each list is cycled with each year. Unlike tropical cyclones in other parts of the wor


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