Rolly brings high risk of storm surges to several areas, including Manila

Typhoon Rolly brings high risk of storm surges to several areas in its path, including Manila.

In its 8 p.m. report on Sunday evening, PAGASA said there is a high risk of a storm surge of more than 3 meters over the northern coastal areas of Quezon, including Polillo Islands, Camarines Provinces, and Catanduanes within 24 hours.

There is also a high risk of a storm surge of 2.1 to 3.0 meters over the coastal areas of Manila, Cavite, Bulacan, Pampanga, Bataan, the southeastern coastal area of Batangas, and the southwestern coastal area of Quezon.

A storm surge of 1.0 to 2.0 meters is also expected over the coastal areas of Aurora, Zambales, Occidental Mindoro, the rest of the coastal areas of Bicol Region, Batangas, and Quezon.

The weather agency said this may result in life-threatening and damaging coastal inundation.

The center of Rolly is forecast to make landfall over Catanduanes on early Sunday morning and then pass over mainland Camarines Provinces on Sunday morning and over mainland Quezon on Sunday afternoon.

Signal No. 4 is up over Catanduanes and Camarines Sur, while storm signals are up over several other areas.

What is a storm surge?

A storm surge is an abnormal rise of the ocean generated by a weather disturbance such as a tropical cyclone, over and above the predicted high tide mark. The US National Weather Service says that the rise in water is mainly wind-driven and therefore, the stronger the winds brought by a typhoon, the higher the storm surge.

Along with sustained wind speeds, another critical factor is the size of the typhoon itself. The bigger the typhoon, the longer it will have an impact on a particular area as it moves along. Size will have a direct correlation with how long the storm surges will be in effect.

A coastal area with a very gentle slope — beaches where you can walk a hundred meters and the water will still only be up to your waist — is more prone to storm surges.

In contrast, beaches with steep ocean floors will be less prone to surges.

Barriers — man-made seawalls and breakwaters and natural mangroves and wetlands — also help block storm surges up to a certain extent.

Typhoon Pedring in 2011 caused storm surges to flood the Roxas Boulevard baywalk and Hotel Sofitel by up to 4 feet. The surges would have been higher, if not for the Manila Bay breakwaters and seawall. —JST, GMA News