FOR TROPICAL countries found near the equator like the Philippines, cyclones are inevitable visitors during the rainy season.

The database of the Citizen’s Disaster Response Center, a local non-government organization advocating disaster management, showed that cyclones affected more than 10 million people, making it the leading disaster in terms of affected population.

The Philippine Atmospheric, Geophysical, and Astronomical Services Administration (PAGASA) has set four categories for classifying tropical cyclones according to intensity: tropical disturbance, tropical depression, tropical storm, and typhoon.

As the country’s weather agency, PAGASA monitors the weather situation in the country, as well as disturbances that might enter the Philippine area of responsibility, in which they are commissioned to observe and supervise its activities.

The life of a cyclone starts as a low-pressure area, an atmospheric activity that brings winds and rains. Low air pressure causes air to rise and condense which eventually leads to precipitation.

Gaining its strength, the disturbance turns into a tropical depression which is another weak disturbance characterized by thunderstorms, a weather activity with the presence of lightning and thunder. It has a distinct circulation speed of up to 63 kilometers per hour but has no eye.

The eye is the calm region of the cyclone found in the center and is characterized by mild winds and lucid skies.

A tropical depression grows to become a tropical storm when its circulation speed reaches 64 to 118 kilometers per hour, with the shape of the cyclone starting to become noticeable.

Finally, the tropical storm officially becomes a typhoon when its speed exceeds 118 kilometers per hour. The typhoon then develops an eye surrounded by an eyewall, the area where the strongest thunderstorms and winds occur.

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According to the website of the Classroom of the Future, an agency which serves as the research center of the National Aeronautics Space Administration (NASA), hurricanes or typhoons start as tropical storms occurring in the tropical zone. Typhoon winds begin to rotate after a sufficient amount of heated moisture is gathered in the atmosphere. It further gains size and force as it absorbs moisture from the surface.

Because cyclones only strengthen in a region where the water measures 74 degrees Fahrenheit or more, it usually loses its power as it moves in cooler region.

“When a hurricane crosses land or cooler waters, it loses its source of power, and its wind gradually slow until they are no longer of hurricane force—less than 74 miles per hour,” the website of the agency stated.

Colors of information

Aside from the storm signals being issued by PAGASA, the agency recently devised a new way to better warn the public through color-coded warnings called Rainfall Warning System (RWS).

The purpose of the new system is to inform the concerned communities’ citizens and leaders about the occurrence of strong and heavy rainfall and help them make appropriate decisions given a particular weather condition.

“[The RWS is] to provide easy-to-interpret information that allows individuals and communities to protect their lives and properties,” said Ma. Cecilia Monteverde, senior weather specialist of PAGASA.

The rain water is collected and goes to the bottom of the funnel where a rain gauge, a device used to measure the length of rainfall, is located.

A yellow warning is raised when rain measuring 7.5 to 15 millimeters is observed in an hour and is expected to continue for the next two hours. This is a warning that people concerned must keep on observing the weather condition.

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If an intense rain measuring 15 to 30 millimeters have been observed for an hour and is also expected to carry for two more hours, the signal is elevated to an orange warning, which prompts affected citizens to be ready for evacuation.

Lastly, a red warning is given when rain measures more than 30 millimeters and is also expected to last for the next two hours. This will mean the community has to evacuate the soonest time possible.

Initially, the RWS had the colors yellow, green, and red, but eventually, green was replaced with orange.

“The color orange was adopted as it is a more appropriate representation of the severity of the situation,” said Nathaniel Servando, PAGASA administrator. Altir Christian D. Bonganay

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