Storm surge or tsunami?

Storm surge or tsunami?
A ship washed ashore by storm surges during the height of Super Typhoon Haiyan (Yolanda) sits atop crushed houses in Tacloban.

MANILA, Philippines-Storm surge or tsunami? Let the Palace tell the difference.

Malacañang on Thursday asked the public to go easy on interchangeably using "storm surge" and "tsunami," apparently to refer to the sudden and violent rise of water levels as what destroyed coastal areas in Leyte, Samar and neighbouring areas recently.

Quoting Secretary Mario Montejo of the Department of Science and Technology, Communications Secretary Herminio Coloma said a storm surge "requires organised evacuation that can be undertaken within a 24- to 48-hour preparation period while a tsunami alert requires outright, spontaneous evacuation where the lead time can be as short as 30 minutes."

"There is an important difference," Coloma said in a press briefing. "So that in communication, we cannot just casually say that storm surge is like tsunami. I hope the clarification is sufficient."

In the aftermath of Supertyphoon "Yolanda," there came suggestions to describe a storm surge as a tsunami if only to alert them more effectively, especially given images of the powerful tsunami that hit Japan in 2011.

The National Oceanic and Atmospheric Administration describes a tsunami as "a series of ocean waves generated by sudden displacements in the sea floor, landslides or volcanic activity."

A storm surge is "an abnormal rise of water generated by a storm, over and above the predicted astronomical tides," according to the National Hurricane Center.

"Storm surge is a very complex phenomenon because it is sensitive to the slightest changes in storm intensity, forward speed, size (radius of maximum winds-RMW), angle of approach to the coast, central pressure (minimal contribution in comparison to the wind), and the shape and characteristics of coastal features such as bays and estuaries," the centre added.

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