Between a tornado and a storm: The rare phenomenon that is 'Gener'

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InterAksyon.com
The online news portal of TV5

MANILA, Philippines -- (UPDATE - 2:58 p.m.) A rare weather disturbance called a shallow low-pressure area or “mesoscale cyclone” was the reason why Metro Manila was pounded by strong winds and rains overnight Sunday to early Monday.

Weather forecaster Fernando Cada said the SLPA was formed near Subic, Zambales by the combined effects of the southwest monsoon and tropical storm "Gener". What resulted was something between a tornado and a storm.

"The SLPA passed by the Manila area. Its center almost passed directly by Metro Manila triggering heavy rains and strong winds" that gusted up to 60 kilometers per hour, or speeds equivalent to a tropical depression, Cada told Interaksyon.com.

The strong winds that struck the metropolis overnight caused power outages in a number of areas. The heavy rains also raised water to near-spilling levels in several dams and prompted the suspension of classes in Metro Manila and nearby regions.

"Parang binagyo ang (It was like a storm struck) Metro Manila within only two to three hours," he said.

However, Cada said no storm warning was raised because the SLPA lasted only "two to three hours" before dissipating when it hit the Sierra Madre mountain range in Quezon.

The Philippine Atmospheric, Geophysical and Astronomical Services Administration said although rare, an SLPA can occur again given the right conditions.

Tornado-like

What was felt in Metro Manila and outlying regions was a combination of the "mesoscale cyclone," which accounted for the heavy rains, and a "surge of the southwest monsoon," which brought the strong winds.

Unlike a tornado, which is often localized, the SLPA that hit Metro Manila affected several cities but did not develop into a full-blown storm. 

Within a storm are vortices that, given the right atmospheric pressure, can develop into “mesoscale cyclones,” multiple thunderstorms that can eventually develop into full-blown storms.

PAGASA said mesoscale cyclones cannot be predicted but added they were able to immediately warn residents in affected areas.

“Mesoscale siya, ‘di siya talaga ma-predict. Nakikita natin kung saan merong ulap at thunderstorm pero ‘di natin alam na bigla siyang magbibigay ng ganitong epekto ng hangin o ulan in a short amount of time (It’s a mesoscale and impossible to predict. We can see where there are clouds and thunderstorms but we cannot know that it will have this effect of wind and rain in a short amount of time),” Cada said.

Rare

Cada said the weather disturbance that struck Metro Manila is rare and usually occurs during the peak of the southwest monsoon or habagat from July to August. “May karagatan sa Manila Bay pero very rare nga ‘yun (mesoscale cyclone) kasi ang bagyo talagang nabubuo sa eastern section o sa East Philippine Sea (Yes, there is Manila Bay but it is really very rare because most typhoon form off the eastern section or the East Philippine Sea),” Cada said.

He said climate change should not be immediately blamed for the phenomenon.

In the past, PAGASA had no equipment to monitor the formation of such small cyclones. But the Doppler Radar it acquired has allowed it to do so.

 “Tina-try naming pag-aralan kung bakit biglang nagkaroon ng ganito (We are trying to study why this suddenly happened),” Cada said.

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