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It’s not the amihan or the kick from an exiting weather system that has dumped a record 82.3 mm of weekend rainfall over Palawan, including Puerto Princesa City. The culprit, according to the state weather bureau is an “equatorial trough.”

Local weather chief Sonny Pajarilla of the  Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) explained that the massive rains were not caused by the northeast monsoon or amihan nor the tail-end of frontal system as both weather systems would only affect the eastern side of the country, which is contrary to the area of Palawan which is in western side.

“Hindi amihan ‘yon, hindi rin tail-end (of frontal system) dahil ang tail-end ay dito lang sa eastern part. Kagabi kaya meron tayong mga massive na pag-ulan, hanggang ngayon meron pa rin pag-ulan dito sa Kalayaan islands, iyan ay dulot ng tinatawag na equatorial trough,” Pajarilla said.

“Hindi talaga siya low-pressure pero mababa ang pressure kaya meron converging winds from various directions, meron southeast, east at northeast na prevailing natin,” he added.

The amount of rainfall recorded at 82.3 mm is higher than the average rainfall during month of January which is 36.4 mm.

The volume of rain is about 226 percent of the monthly rainfall for the month of January and is 126 percent higher than the average, Pajarilla said.

“Almost 200 percent siya kesa sa ating normal rainfall, kapag sinabing normal ay average na pag-ulan na ating nararanasan sa isang buwan for the past 30 years,” he said.

Pajarilla added that the equatorial trough has oscillated and mostly cloudy skies will be observed throughout the day. There are still rains and thunderstorms to be expected during noontime but not as massive as experienced on Sunday evening.

The equatorial trough is possible to be experienced again due to the intensity of easterlies under La Niña, Pajarilla said.

“Nagmo-move kasi yong ating atmosphere, yong atmospheric flow kung tawagin para siyang alon kaya may wave-wave siya. Kung tayo ay napapaloob don sa trough ay nagkakaroon ng tuloy-tuloy na development ng pag-ulan,” he said.

PAGASA is not expecting any storm development within this week and gale warning advisory is still raised over the seaboard of Kalayaan island.