Sunday 28 October 2012

Hurricane Sandy heads towards east coast of America.

Hurricane Sandy crossed the Caribbean last week leaving at least 21 people dead, in Jamaica, Haiti, Cuba and the Bahamas. It was thought likely to make landfall in the US this weekend, hitting the coast of either Florida or South Carolina, but instead veered to the east, before moving northward again. It is now thought that it will hit the US coast on Monday 29 October, somewhere between Washington DC and New York. The storm is currently classed as a Category 1 Hurricane, which implies a storm with sustained winds in excess of 119 km/h, but this does not do justice to the scale of the storm, which is several hundred km across and moving slowly northward; a hurricane can have fast winds yet still move slowly as these winds are circular, moving about the centre of the storm. Slow moving storms are more dangerous as they expose any given area to the effects of the hurricane for longer.

Map showing the predicted path of Hurricane Sandy. The blue area is the margin of error; it stops at the Canadian border, but the hurricane is unlikely to. Red areas are likely to suffer flooding. Google Crisismap.

Sandy is being described as the biggest storm ever to hit the United States, which may-or-may-not be hyperbole, but certainly has the potential to be extremely destructive, as it seems inevitable that it will hit northern cities that are not as well prepared for hurricanes as their southern counterparts. Whilst the high winds associated with hurricanes are extremely dangerous, the real danger from such storms is  the flooding. Each millibar drop in air pressure can lead to a 1 cm rise in sea level, and large hurricanes can be accompanied by storm surges several meters high. This tends to be accompanied by high levels of rainfall, caused by water picked up by the storm while still at sea. Due to this the authorities along much of the US eastern seaboard are trying to organize evacuations of low-lying coastal areas, with mixed results in states that are unused to hurricanes.

Hurricane Sandy has already caused both candidates in the US presidential election to adjust their schedules, and may yet have a more profound, long term effect on US politics. It seems inevitable that the storm will be extremely destructive, possibly more so than any event the United States has previously encountered, and rebuilding after such an event is likely to prove a challenge (though not one beyond the means of the nation). This exceptional size and behavior of Sandy has widely been attributed to global warming, which, coming at the end of a season of extreme weather events, may make this more of an issue in future American elections than has been the case to date.

Hurricanes, and tropical storms in general, form due to heating of air over the sea in tropical zones. As the air is heated the the air pressure drops and the air rises, causing new air to rush in from outside the forming storm zone. If this zone is sufficiently large, then it will be influenced by the Coriolis Effect, which loosely speaking means the winds closer to the equator will be faster than those further away, causing the storm to rotate, clockwise in the northern hemisphere and anticlockwise in the southern hemisphere.

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