Sunday, 15 March 2015

At least eight dead as Cyclone Pam sweeps across Vanuatu.

Eight people are known to have died and it is feared that the death toll will rise sharply after Cyclone Pam swept across the island nation of Vanuatu early on Saturday 14 March 2015. The confirmed deaths are all in the capitol, Port Vila, where most of the city's buildings have been destroyed and where it is thought likely that the number of dead will reach several dozen, and it is likely that many people will have died in more remote areas on the 83 inhabited islands of the nation. Unconfirmed reports from the United Nations Office of Coordination of Humanitarian Affairs for the Pacific suggest that over 40 people have died in the northeastern province of Penama, which has three main populated islands, Ambae, Maewo and Pentecost.

Damage in Port Vila, Vanuatu, following the passage of Cyclone Pam. Reuters.

Cyclone Pam is recorded to have been a Category Five storm as it passed across Vanuatu, that is to say a storm with sustained windspeeds in excess of 250 kilometers per hour (a sustained windspeed is defined as a windspeed recorded continuously for periods in excess of a minute) and gusts of up to 300 kilometers per hour. It is currently moving towards the northern coast of New Zealand, though it has been downgraded to a Category Three storm (which produces sustained winds of 178-208 kilometers per hour). As well as the damage caused in Vanuatu, Cyclone Pam is reported to have caused major damage in Kiribati and the Solomon Islands as well as flash floods in Tuvalu.

The passage of Cyclone Pam till 2.04 GMT on Sunday 15 March (thick line) with its predicted future path (thin line, circles represent the margin of error on the predictions). Colours indicate the strength of the storm. Tropical Storm Risk.

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 inrushing 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 the waterfront in Port Villa in the aftermath of Cyclone Pam. Reuters.

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.

Australia, New Zealand, the United Kingdom, France, the United Nations and the European Union have already pledged aid to help Vanuatu recover from the effects of Cyclone Pam, and Oxfam, Save the Children, UNICEF, the Red Cross and other agencies have began collecting donations from the public to help with the relief effort.

See also...

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Cyclone Evan hit the island of Samoa on Thursday 13 December 2012, leading to widespread flooding and causing the Vaisigano River to burst its banks in the...

Heavy rainfall associated with Cyclone Grant (now downgraded to Tropical Storm Grant) has caused serious problems along the Edith River in...

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