Frankenstorm: Why Is Hurricane Sandy So Big?
Updated: 3:41pm UK, Monday 29 October 2012
A number of complications have caused Hurricane Sandy to grow into a menacing monster storm which is threatening to become the biggest in US history.
Sandy, which is hundreds of miles across, is set to merge with other weather systems, unleashing a deadly punch of high wind, heavy rain, extreme tides, several days' worth of snow and potentially deadly storm surges.
On course to interact with Sandy is a wintry storm moving across the US from the west and frigid air streaming south from Canada.
New York and Long Island could see huge seawater surges of up to 11 ft (3 m) which coincide with high tides due to a full moon.
Sky News Weather producer Christopher England said these factors makes Sandy "unusually intense".
"It's a major storm that's going to hit a major place - and it will hit New York City at high tide, due to a full moon, causing a massive storm surge," he said.
England said most hurricanes that hit America's biggest city tend to make landfall further south, so they weaken before hitting the Big Apple.
"Most storms don't come from over the ocean, like Sandy is. They tend to hit land earlier, often around North Carolina, and lose their strength," England said.
"It's often the decaying remnants that hit New York - rather than the full-blooded storm.
"But Sandy has maintained its strength because it has kept its track up over the ocean."
England said another major issue making Sandy worse is the fact the air is set to be colder than usual.
"A storm's energy comes from temperature and humidity differences in the atmosphere - essentially warmer air rises and condensing water vapour adds to the energy and drives the storm," he said.
"Sandy is moving into a region with a strong flow from the Arctic, so will be coming into contact with much colder than average air causing the potential for greater temperature contrasts, and hence greater energy release and a more potent storm."
While Sandy does not yet pack the punch of Hurricane Katrina, which devastated New Orleans in 2005, it could become more potent as it approaches the US coast.
And England said the storm is unlikely to change its path.
"It could change track, but it doesn't seem likely," he said.
"It's possible that the worst-case scenario will not happen - it all depends on how it comes together.
"But it certainly looks like it's going to be a big event."
Sandy killed 66 people in the Caribbean before pounding US coastal areas with rain and triggering snow falls at higher elevations.