Thursday 29 August 2013

At least one dead as Tropical Storm Juliette crosses the tip of Baja California.

Tropical Storm Juliette crossed the tip of Baja California in Mexico on Thursday 29 August 2013, brining winds of up to 65 kph and heavy rains which lead to localized flooding and power outages. One man is reported to have died as a result of electrocution; details of this event are not clear, though officials have reported that the practice of running illegal wires from mains power supplies is common in the area where he died.

The path of Tropical Storm Juliette till 9.00 pm GMT on Thursday 29 August 2013 (thick green line) and its projected future course (thin blue line). 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.

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.

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