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Deluge with no name threatens Ondoy's place in history

August 8, 2012 9:34pm
(Updated 8:52 a.m., August 9) - The annual monsoon rains brought in by the "Habagat" winds are such a regular occurrence that they don't stand out enough in the popular imagination to merit a unique name, as is the case with storms and typhoons. 

So how did it happen that the impact of the 2012 monsoon rains this week may surpass  the epic floods of Tropical Storm Ondoy in 2009?
 
“If there’s any message that we should learn… even a ‘simple’ monsoon can cause severe damage,” Nathaniel Cruz, GMA’s resident meteorologist, said in an interview.

This has been no ordinary monsoon or habagat.
 
From Aug. 6 to 7, a 48-hour period, the total accumulated rainfall amount recorded at PAGASA (Philippine Atmospheric Geophysical Services Administration) Science Garden was 687 mm. 
 
This amount is higher than the 24-hour accumulated rainfall on Sept, 26, 2009 —the day when Tropical Storm Ondoy devastated Metro Manila and other neighboring provinces. At PAGASA’s Science Garden, the recorded rainfall that day was 455 mm.

Ondoy featured more volume per hour but over a shorter time period. After starting on Monday, and intensifying on Tuesday, the habagat-induced rains this week are still not over, as a torrential downpour fell for several hours on Wednesday afternoon, after a short respite in the morning.

"This is already worse than Ondoy," declared Jose Fabian Cadiz, the vice mayor of Marikina, which sits in a valley that was hammered by the infamous "one-hundred-year rain" in 2009. "In half a day, Ondoy was over, the water began to subside. Now, we have already been submerged for three days, and the water is still high."

Communities from Cainta to San Fernando, Pampanga are drenched in agony, and tortured by the uncertainty of when the rains will end.

In both rainfall and notoriety, this nameless monsoon is threatening Ondoy's place in history.
 
However, the rainfall amount is just one point of comparison, said GMA Weather Group consultant Karen Cardenas. What has happened last Monday, Tuesday, and Wednesday was completely different from Tropical Storm Ondoy: the latter was a “legitimate weather disturbance,” while the former was an abnormally huge amount of torrential monsoon rains.

Weather phenomena that mated and produced a monster
 
The monsoon was "enhanced" by a typhoon north of the Philippines, in the peculiar language of meteorologists, as if they were weather phenomena that mated and produced a monster.
 
According to PAGASA, the torrential rains were caused mainly by the Southwest Monsoon, also known as Habagat, intensified by Typhoon Haikui.
 
The Southwest Monsoon (SW Monsoon) is defined by PAGASA as “affecting the country from July to September, is very warm and humid, occurs when warm moist air flows over the country from the southwest direction, is characterized by heavy rainfall that may last for a week. It brings the rainy season to the western portion of the country.”
 
During this period, the land temperature in mainland Asia is higher so the sea breeze from the oceans (mainly Indian and Arabic Oceans) tends to move toward the land. This movement causes heavy rainfall, Cruz explained.
 
Since Typhoon Haikui moved slower, Cardenas explains, it was able to accumulate more water, increasing its power. As the typhoon strengthened, and approached the SW Monsoon, the monsoon intensified, carrying a huge amount of rain.
 
Above normal, against Ondoy
 
Dr. Mahar Lagmay of Project NOAH (Nationwide Operational Assessment of Hazards) said earlier that these types of phenomena occur once every fifty years.
 
The amount of rainfall recorded from Monday to Tuesday for a 48-hour period surpassed the monthly precipitation limit of Metro Manila, said Cruz. 
 
For one, in the normal values for rainfall in Manila, as recorded in Port Area, Manila is between 400-500 mm during the month of August. 
 
Weather.com, on the other hand, says that the average rainfall for the month of August should be within 300-400 mm.
 
However, Cardenas and Cruz said that even if what happened during the past few days may be similar to that of Tropical Storm Ondoy, the comparison should be made using specific parameters such as the same weather station used in comparing the amount of rainfall, the context of both events, status of dams during both period, and the saturation levels of rivers, tributaries and other areas.
 
Last week, Metro Manila was also affected by a weather disturbance. Tropical Storm Gener’s (Saola) strength was between 120 to 150 kph. According to PAGASA, the recorded highest rainfall amount that time was in Puerto Princesa, on July 28, at 106.3 mm. In PAGASA’s Science Garden, the recorded amount of rainfall that day was 50.4 mm.
 
Tropical Storm Gener lowered the saturation points of most of the water systems in Metro Manila and nearby provinces, Cardenas said. There was no immediate weather disturbance prior to the onset of Tropical Storm Ondoy. — TJD/HS/KG, GMA News
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