Hurricane Sandy is posing a monster challenge for weather forecasters and emergency agencies, due to an amazing combination of meteorological factors, but what's just as amazing is how well they've been able to predict what seemed to be an unpredictable disaster.

"It looks like we've been fairly consistent on this, even five days out," Chris Landsea, science and operations officer at the National Hurricane Center in Miami, told me today. "I think when all is said and done, on the track forecast, we're going to be quite accurate."

Sandy's path, which took a left turn from the Atlantic to slam head-on into the heavily populated Northeast, is just one of the unusual aspects of this storm. "The size of this system, the late-season nature, and the track — all these are fairly unique characteristics," Landsea said. To look for precedents, you have to go back to infamous hurricanes such as Agnes in 1972, Hazel in 1954, even the great storms of 1944, 1938, 1815 and 1804. But today, the region is so much more populous and developed that the impact is certain to be far greater.

Here are five factors that have turned Sandy into a superstorm:

Northerly track: Atlantic tropical storms most commonly tear through the Caribbean and the Gulf of Mexico, and lose energy as they pass over the U.S mainland. This storm, however, crept along the Eastern Seaboard, where waters that were warmer than usual for this time of year kept the storm alive. As the storm moved northward, it morphed into a hybrid storm, drawing additional strength from the differential between the storm's warm air and cold northern air from the jet stream.

"There's a transformation that this system is undergoing," Landsea explained. "This is actually evolving into a winter storm, and later, a nor'easter." One result of this evolution is that the storm system has widened to more than 800 miles in diameter, stretching from the Carolinas to Maine and Canada.

NASA / NOAA

NOAA's GOES-13 weather satellite shows the storm system associated with Hurricane Sandy covering the northeastern United States even before landfall on Monday.

The left turn: Hurricanes that get so far north could drift off into the cold Atlantic to die — but they can also be pushed into the mainland, as Hurricane Irene was last year. Irene followed a path that was roughly parallel to the coastline, but Sandy took a hard left turn that put it on a course for a direct, perpendicular strike on the coast. That's because a cold front on the mainland is drawing the storm westward, while the current state of a weather pattern known as the North Atlantic Oscillation is blocking the storm from heading eastward. 

Storm surge: Sandy's top sustained winds of 85 miles per hour typically wouldn't rate as a superstorm, but its effects will be magnified, Landsea said. "Even though it's not a 'major' hurricane by any means ... there is substantial threat because of the storm surge and because of the rainfall. There's going to be flooding. Both of those factors are going to be killers," he said. The storm surge is projected to range from 6 to 11 feet. One of the big reasons for such a high surge is that the waters off the coast of New York and New Jersey are so shallow: As the surge from the deeper ocean nears the coastline, all that water piles up to create a higher wave.

Full moon: Another reason for the huge storm surge is the fact that the moon is hitting its full phase just as Sandy is making landfall. The celestial lineup of the sun, moon and Earth contributes to higher-than-normal high tides. 

Winter storm: Sandy is such a late-season storm that it's running into winter weather in the northeastern United States, which is adding an extra dimension to the misery. "I have not been around long enough to see a hurricane forecast with a snow advisory in it," Craig Fugate, administrator of the Federal Emergency Management Agency, told NBC's TODAY. The storm could trigger up to 3 feet of snow in the Appalachians, the National Weather Service reported. The Weather Channel's Tom Niziol said that "an amazing combination of factors" have come together to make Sandy a threat due to the snow as well as the rain.

Landsea and other forecasters may marvel at the factors behind what some have called a "perfect storm" or "Frankenstorm," and there'll surely be lots of lessons learned for future weather modeling. But that's not what's uppermost on their mind right now. "What's really important are the impacts," Landsea said.

To keep on top of the storm, and to keep safe, keep an eye on NBC News' hurricane coverage:

• Sandy swamps coastal towns, cuts power to 700,000
• Live updates on Hurricane Sandy
• Your images of Hurricane Sandy

Update for 3:10 p.m. ET Oct. 30: The storm surge was clearly one of the biggest impacts of Hurricane Sandy, and for good reason: The National Hurricane Service reported that in some cases, the surge exceeded its own maximum prediction of 11 feet. At New York's Battery Park, for example, the surge measured 13.7 feet — and it was devastating. On another note, I've corrected the spelling of Landsea's apt last name since this item was originally published.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

Did forecasters, policymakers and media types overhype Hurricane Irene? It's not just a meteorological question: The debate over whether the outlook for damage was overhyped, or hyped just right, touches upon issues of risk perception and even the climate change debate. Like most natural disasters, Irene's deadly sweep over the U.S. East Coast has left behind some important lessons for researchers as well as regular folks.

Here are some of the lessons that Monday-morning commentators are chewing over:

What was right and wrong about storm prediction?
The computer models, and the meteorologists who wielded them, put in a "gold medal" performance when it came to predicting Irene's track — but there was much more uncertainty about the intensity of the storm. That's typical for tropical storms, said Frank Marks, director of the Atlantic Oceanographic and Meteorological Laboratory's Hurricane Research Division. "Irene really exemplified the issues that we've been trying to tackle," he told me.

Hurricanes typically follow a pattern in which an outer ring of storms will tighten up to replace an inner ring surrounding the hurricane's eye, intensifying the storm system in the process. In Irene's case, that pattern (known as eyewall replacement) was interrupted, and the storm didn't gather as much strength as most of the models suggested. "Some of the models did represent it well," Marks said, but there wasn't enough confidence in those models to change the storm forecast.

Researchers have been working to reduce the error rate for hurricane track and intensity forecasts through the Hurricane Forecast Improvement Project, with the goal of a 50 percent reduction from 2008 levels by 2018. The University of Washington's Cliff Mass, an expert on weather modeling, said Irene showed that much more progress still has to be made on predicting a storm's intensity.

"The classic is good forecast for track, bad forecast for intensity," he told me. "Let's face it: This happens all the time. ... To get the intensity right, you have to be able to predict the inner workings of the storm, and that's what we don't do well yet."

But Mass said "we didn't even need the models" to know that Irene would become less intense as it moved up the coast, through the increasingly cool waters of the Atlantic. In fact, Mass contends in a blog post today that "there is really no reliable evidence of hurricane-force winds at any time the storm was approaching North Carolina or moving up the East Coast."

He argued that the National Weather Service should have downgraded the storm much more quickly than it did. "There's a tendency to be conservative," he told me. "We have to learn to be more nimble."

Did forecasters overhype the storm?
In his blog posting, Mass addresses the hype surrounding Irene: "Considering the tendency for media to hype storms, it is crucial for meteorologists to stick to the exact story and not overwarn in the hope of encouraging people ot take effective action. If the storm was known not to be a hurricane earlier, might the mayor of NY have held off closing the city down, thus saving billions of dollars?"

Marks said that the storm was assessed based on readings taken from above as well as on the surface, and that the National Oceanic and Atmospheric Administration followed the standard procedures for those assessments. But he acknowledged that Irene was a tough storm to classify, in part because of its breadth. "From Cape Cod all the way inland to Pennsylvania — just think about the energy," he said. "It's really the energy of the storm, it's not the peak wind."

He said spin control isn't part of NOAA's mission. "We provide as much information as we can, based on what we know," Marks said. "What the public and decision makers do with that information is something that's out of our purview."

Marks acknowledged that some of the reports made the storm sound scarier than it really was. "If you looked at those scenarios that the media was getting ... the disaster scenario was extreme. That was for a major hurricane coming straight at them, not a weakening storm coming up the coast," he said.

How much was lost in translation?
So was this a case of journalists and policymakers making too much of the storm? Maybe so, said David Ropeik, a consultant on risk perception, Big Think blogger and author of the book "How Risky Is It, Really?" But maybe that's not so bad.

"Yes, the information the media presented was wrapped up in breathless alarmism," Ropeik, a former msnbc.com contributor, told me. "But we forget two things: First, surveys show that the public knows that about the media. And second, under all the alarmism was really important information that helped people stay safe: storm track timing, tips for preparedness, evacuation routes. It was alarmist in voice, but an informative tool. And that probably helped more than it hurt. ... There was no panic, there was no hysteria."

Ropeik said government officials also did the right thing: "In my opinion, they were overly precautionary, but most people want them to do that. One can only measure the accuracy of their precaution in hindsight, and you don't want to err on the wrong side. ... The evacuation, the closing of the subways, you don't want to make a mistake on that in the wrong direction."

There were political considerations, to be sure. Just ask New York City Mayor Michael Bloomberg, who faced harsh criticism over the lack of preparedness for last winter's snowstorms — or former President George W. Bush, who was similarly criticized in the wake of Hurricane Katrina almost exactly six years ago.

But beyond the politics, the storm's toll — more than 30 dead, plus an estimated $7 billion in property damage — clearly demonstrates that Irene was more than just hype.

"I daresay the people who are saying there was overreaction are not those who are still without power, or who suffered property losses, or who lost loved ones," Ropeik said. "Risk is a matter of perception. It depends on who you ask."

Some commentators worry that hyping hurricanes will lead folks to disregard future warnings as a case of "crying wolf," but Ropeik said the public response to the warnings about Irene "puts the lie to that."

"Other storms have been hyped, and have not panned out, and yet people still took reasonable precautions this time," he said. "The 'cry-wolf' thing didn't happen."

Do more big storms lie ahead?
The concerns about Irene's effects could hint at the shape of climate debates to come.

Research published last year in the journal Nature Geoscience suggested that global warming was likely to produce fewer but stronger tropical storms. This year, a study in the journal Science came to a similar conclusion.

Such projections have sparked strong debate, as most claims about climate effects have done. It's impossible to link any single event, such as Irene or Katrina, to long-term climate trends. But in a posting to his Desmog Blog, science writer Chris Mooney argues that Hurricane Irene should get people thinking about what lies ahead:

"... Irene focuses our attention on our serious vulnerability, and we need to seize that moment — because too often our default position is to act like nothing bad is going to happen.

"There are several places in the United States, besides New Orleans, where a strong hurricane landfall could be absolutely devastating. These include the Florida Keys, the Miami-Fort Lauderdale area, Tampa Bay/St. Petersburg and Houston/Galveston. But they also include some East Coast locations, and chief among these is New York/Long Island. ...

"So what are our major coastal cities doing to protect themselves? That's the question we should all be asking right now."

What questions are you asking? Share them as a comment below, and we'll see if we can get a discussion going.

Update for 5:30 p.m. ET: One of the first Irene-related research projects to come to light focuses on whether big storms could actually counteract the effects of greenhouse-gas emissions.

Scientists at the Stroud Water Research Center and the University of Delaware are sampling the storm runoff at sites along creeks in Delaware to measure how much carbon is being transported. In a news release, the National Science Foundation says the project could reveal how much of a role soil erosion plays in sequestering carbon to prevent it from re-entering the global carbon cycle.

"The bigger the storm, the greater the disproportionate load, so you might have a single 100-year storm event move 25 percent of the material for an entire decade," said Anthony Aufdemkampe, a scientist at the Stroud Water Research Center. "This is important, because fresh waters and the carbon they transport play a major role in the global cycling of greenhouse gases."

Update for 6:30 p.m. ET: Climate Progress' Joe Romm notes that rising sea levels, which some see as an effect of global climate change, would heighten the destructive effect of coastal storms such as Irene because the storm surge would come on top of those higher seas. (The state of global sea levels is another subject of scientific discussion.)

More about Irene's aftermath:

• Twitter's top lessons from Hurricane Irene
• Readers capture Hurricane Irene
• Hurricane Irene spawns baby boom
• Stocks close sharply higher after Irene passes

Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding me to your Google+ circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.