PAGASA's eye to the sky: How state weather forecasters monitor storms

After tropical cyclones Auring, Bising, Crising, Dante, and Emong, the rain-drenched nation asks: Will there be more?

 

Weather experts say there will be. Each year, about 20 tropical cyclones enter the Philippine Area of Responsibility (PAR).

 

“However, only six to nine out of the 20 typhoons make landfall,” said Rene Paciente, Chief of Weather Forecasting and Warming system of Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA).

 

“We issue information on [the] tropical cyclone even before it enters the PAR,” Paciente told the media participants of the seminar workshop convened by the Department of Science and Technology and PAGASA in Davao City last week.

 

A tropical cyclone is an intense low pressure system with minimum sustained winds of 35 kilometers per hour (kph). 90 percent of the typhoons that enter the PAR affect the country.

 

The briefing paper distributed during the workshop stated that winds do the most damage to buildings and settlements, but most casualties result from storm surge and inland flooding that is associated with tropical cyclone.

 

In the Filipino dialect, tropical cyclones are called 'bagyo,' a word which originated from a 1911 storm making landfall in the city of Baguio. The storm had a recorded rainfall of 46 inches within a 24-hour period.

 

Paciente said tropical cyclones are classified according their strength and are determined by the speed of the maximum sustained winds near the center. These are 'tropical depression,' 'tropical storm,' and 'typhoon.'

 

A tropical depression has maximum winds from 35 kph up to 63 kph. A tropical storm is comprised of winds moving anywhere from 64 kph to 117 kph. When these exceed 117 kph, a typhoon ensues.

 

PAGASA issues weather advisories for tropical cyclones. This advisory contains the general information on the presence of a cyclone even if it is still too far away from the country to pose a threat within the next three days. This gives ample enough time to be aware of a potential threat.

 

According to Paciente, the process of forecasting weather can be broken down in five steps. These are:  

 

Step 1: Observation 

The weather bureau, with 68 monitoring stations throughout the country, observes—through instruments and through ocular means—all the weather elements on a daily basis.  “This gives us a picture of what’s happening up there,” Paciente informed.

 

Step 2: Transmission and collection of weather data 

Data on weather observations are condensed into coded figures and symbols for easy transmission to the head office. These are transmitted through radiophones, global telecommunication systems, fax machines, telephones, cellular phones, and electronic mail. 

 

“We exchange raw data with other countries as well,” Paciente said. “As a member of World Meteorological Organization, we have an international agreement to do that. These data come in the form of coded message.”

 

Step 3: Data plotting and weather map analysis

Among those that are observed and plotted are: wind direction and speed, surface pressure, surface temperature, amount and type of clouds, visibility, present and past weather, pressure tendency, and rainfall. When the coded data of these variables arrive, they are decoded and plotted on maps in symbols or numbers. 

 

Observations made over land and seas are plotted into surface maps, while wind observations are plotted into upper air maps. The weather bureau uses an automatic plotting machine for this purpose.

 

Step 4: Analysis of weather maps 

The plotted maps are given to forecasters or analysts, who make the analysis or prognosis based on what’s on the maps. The current weather maps are compared with the weather maps of previous days to establish the movement of weather systems and forecast their development and movement. Only then do the analysts make their prognosis.

 

Step 5: Formulation of the forecast 

The tools used in forecasting include weather maps, satellite imageries, radar observation, numerical weather, and prediction models. The prognosis is put down in writing; this now becomes the forecast. Every day, the weather bureau makes public weather forecasts, forecasts for aviation, as well as marine forecasts for coastal areas.

 

Oftentimes, people only see the bad side of tropical cyclones. But there’s also good side to them. According to Edna J. Juanillo, the chief of PAGASA’s climatology and agrometeorology division, rainfall brought about by tropical cyclones increases the groundwater and water levels of dams.

 

“About 50% of the rainfall of the country comes from tropical cyclones,” Juanillo said. —VC, GMA News