MANILA — Water levels rose outside homes in Tiwi, Albay on Saturday, causing alarm among residents who thought it was a storm surge, an abnormal rise in seawater level. 

However, PAGASA clarified that it was actually "swelling," a natural occurrence that signals an approaching storm.

Richard Orendain, a hydrologist from PAGASA, explained that swelling acts as a warning sign of an incoming storm.

Unlike a storm surge, swelling occurs when a distant storm drives ocean waves toward the shore.

“Malayo pa ‘yung storm, ‘yun ang nagda-drive sa kanya. Makikita natin diyan, it’s a series of waves na medyo mahaba ‘yung wavelength niya… tapos sunud-sunod siya,” Orendain said.

(The storm is still far away but that is what drives the swelling. We can see that it's a series of waves with a rather long wavelength and they come in sequence) 

During swelling, the ocean’s height gradually rises, and waves reach farther inland.

STORM SURGES

In contrast, a storm surge happens when strong winds from a storm near directly push seawater onto land. This results in higher, more forceful waves slamming into the coast.

“Dinadrive niya yung ocean papunta sa dalampasigan hanggang sa lumagpas siya sa mismong dalampasigan at pwedeng umabot ito ng anim na metro mga ganun...Kapag malakas ‘yung hangin, mas malakas ‘yung impact ng storm surge,” Orendain said.

(It drives the ocean towards the coast until it goes past the coast and onto the beach. It can reach as high as six meters. If the wind is strong, the impact of the storm surge is stronger)

READ: Floods in some parts of Bicol due to storm surge