Monday 8 December 2014

At least 21 dead as Typhoon Hagupit sweeps across the Philippines.

Twenty-one people are reported to have died in the  the Philippines, as a result of Typhoon Hagupit (known locally as Typhoon Ruby), according the Philippine National Red Cross. The majority of the victims are said to be in the municipality of Borongan in Eastern Samar, where 16 people have lost their lives, with two other fatalities on the island of Samar and three in the province of Iloilo on the south of Panay Island. The majority of the victims are reported to have drowned in a storm surge caused by the typhoon, and it is though that the number of deaths would have been much higher but for a massive evacuation of low-lying areas organised by authorities in the Philippines.

 Storm surge on a beach at Legazpi in Albay Province on Sunday 7 December 2014. Aaron Favila/AP.

Typhoon Hagupuit made landfall on Saturday night near the town of Delores in Eastern Samar, bringing with it winds gusting at up to 170 km per hour, but lost energy as it past over the islands, with the highest wind speeds recorded as it passed over Manila on the west coast of Luzon Island being about 135 km per hour.

Damage to homes in Delores in East Samar Province, caused by Typhoon Hagupit. EPA.

Tropical storms are caused by solar energy heating the air above the oceans, which causes the air to rise leading to an inrush of air. If this happens over a large enough area the in rushing air will start to circulate, as the rotation of the Earth causes the winds closer to the equator to move eastwards compared to those further away (the Coriolis Effect). This leads to tropical storms rotating clockwise in the southern hemisphere and anticlockwise in the northern hemisphere.These storms tend to grow in strength as they move across the ocean and lose it as they pass over land (this is not completely true: many tropical storms peter out without reaching land due to wider atmospheric patterns), since the land tends to absorb solar energy while the sea reflects it.

 Damage to homes in Tacloban, in the Eastern Visayas caused by Typhoon Hagupit. Maria Byrne/BBC.

The low pressure above tropical storms causes water to rise there by ~1 cm for every millibar drop in pressure, leading to a storm surge that can overwhelm low-lying coastal areas, while at the same time the heat leads to high levels of evaporation from the sea - and subsequently high levels of rainfall. This can cause additional flooding on land, as well as landslides, which are are a common problem after severe weather events, as excess pore water pressure can overcome cohesion in soil and sediments, allowing them to flow like liquids. Approximately 90% of all landslides are caused by heavy rainfall.

See also... Death toll from Typhoon Haiyan nears 4000.                                                          The number of people known to have died after Typhoon Haiyan (known in the Philippines as Typhoon Yolanda) hit the Eastern Visayas islands in the central Philippines on Friday 8 November 2013...
Three people are known to have died and two more are still missing after Typhoon Krosa (known as Typhoon... At least thirteen dead as Typhoon Nari sweeps across the Philippines.                         Thirteen people are known to have died and at least three more are still missing after Typhoon Nari swept across Luzon Island, making landfall on late on Friday...

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