Monday, October 29, 2012

A Record-Breaking Storm

Monday, October 29, 2012
3:06 P.M.

19 years old, and Spongebob is still my favorite cartoon. 

It seems like everywhere I go, people are talking about Hurricane Sandy. Most of what I'm seeing are Facebook posts from people on the West Coast praying for the health and safety of those affected by this massive storm. Some posts are from people who are experiencing the onslaught of the storm. Other posts juxtapose Sandy with other topics, such as the presidential debate or global warming. And of course, there is the occasional egotistical braggart who feels they need to tell the world how sunny and warm the weather is at their locale.

Sonja Breda, one of my good friends who is a freshman at Bryn Mawr in Pennsylvania, updated her status as "I have to say that I love radical weather, so I have been really enjoying watching Sandy's progression as I sit drinking tea with my pals, watching tree branches fly past our windows." Sounds like my kind of woman!!! On the other hand, I asked my friend Alex Dyring, who I thought was living in Boston, what the weather was like there, and he said "I actually live in Spain right now although I'd be happy to give you a report of my sunny day today." And of course, my good friend Nicholas Efthimiadis commented " It's very windy today... We've been so focused on Sandy, we forgot about our own weather." I agree, it has been a tad breezy. But it has been nothing like the East Coast.

Here's the latest satellite image of Sandy, and below that is a video that show's Sandy's development. I believe the loop approximately shows the last ~48 hours up to the time of the latest satellite image below.

NASA GOES 13 Satellite - Valid 2232 UTC, October 29, 2012

As of 2:00 PDT, Sandy was a category one hurricane located at 38.8 N and 74.4 W. It was heading WNW at 28 mph, has maximum sustained winds of 90 mph, and has a pressure minimum of 940 millibars. At some point, the pressure may dip below 940 millibars. Simply incredible. To put things in perspective, the Columbus Day Storm, which was by far the most powerful windstorm to ever strike the West Coast, only got down to 960 millibars. The record for the lowest pressure recorded north of Cape Hatteras is 946 millibars, and was recorded on Long Island during the New England Hurricane of 1938. I'm not sure if this record has been broken, but there is a good chance it will be.

There are, well, a trillion things about Sandy that make it different than your typical hurricane, but I'll just name a few. First off, it is exceptionally large. The Saffir-Simpson Hurricane Scale rates hurricanes based on their central pressure, not wind speed. Since Sandy is so large, the wind is spread out over a huge area, but it isn't as strong as it would be if Sandy was a more compact cyclone. Hurricane Charley, which hit Florida as an extremely strong category four hurricane in 2004, had a minimum pressure of 941 millibars. So to say that Sandy is "just a category one" is misleading. It still has extremely high winds, and the large size of the storm helps to create a storm surge that has already inundated parts of the East Coast.

Second off, the thing that makes Hurricane Sandy different from your typical hurricane is that it is undergoing a transition to an extratropical cyclone. I mentioned this in my previous blog post on Friday, but it is the singular thing that makes this storm so unique. You regular readers of my blog know the whole spiel that I've given numerous times... tropical and extratropical cyclones are extremely different. Tropical cyclones form over warm water where there are minimal horizontal temperature gradients in the atmosphere, and they derive their energy exclusively from the ocean's warmth. Their warmest temperatures are at their core, and they have no fronts. Extratropical cyclones, on the other hand, typically have their coolest temperatures at the core, as the counterclockwise flow (in the Northern Hemisphere) brings cold air originating from the poles right into their low pressure center. Hurricanes and extratropical storms are often called warm and cold core systems, respectively.

What Sandy is doing is undergoing a transition from a warm core storm to a cold core storm. Take a look at some of the pictures below, and you'll see what I'm talking about.

Disclaimer: I got the idea of showing these pictures from Cliff Mass' blog, because I thought he did a good job at explaining it. These are not the exact same pictures and aren't even from the same model run. These are from the Monday, October 29 12z HWRF model and are the charts at 850 mb. They show the geopotential heights (contours, 30m interval), temperatures (color fill, 2 Celsius interval), and wind vectors (m/s).
6 hour forecast

Six hours after the initialization (which was at 12z this morning, so this is chart models the storm as it was several hours ago), the storm has its warmest air at its core, and looks pretty darn symmetrical.

12 hour forecast

Six hours later though, its symmetry is starting to fade and it is getting cooler at the center. Most hurricanes weaken when their warm cores die, but this storm is special because it is actually strengthening off of the horizontal temperature gradients across latitudes. It has a ton of energy and moisture and the gradients are very sharp, so it undergoes explosive cyclogenesis.

18 hour forecast

Six hours after that, the process continues. The warm air at the center is being replaced by cold air.  You can  see the nice "hook" shape, this is due to the occluded front wrapping around the center of the low. This is called the "bent-back occlusion" and is a hallmark of strong extratropical storms.

24 hour forecast

24 hours after the initialization, the process is essentially complete. No more warm air in the center. Cooler air continues to flow in. By this point, the storm is starting to weaken, because the horizontal temperature gradients are weakening due to the evolution of the fronts, but it'll still be strong nonetheless.

The third main thing that makes this storm unique is the fact that it is causing blizzard conditions in the Appalachian Mountains. The National Weather Service is calling for up to three feet of snow in the southern Appalachians above 3,000 feet! That's some crazy stuff right there. You usually don't associate tropical systems with snow. But folks, this is no ordinary storm.

AP Photo/Robert Ray - Snow in the mountains of West Virginia - 10/29/12

I've seen a lot of headlines dubbing this storm the "Superstorm." What makes this storm any more super than other storms? In my opinion, it's just the most incredible, rare, meteorological setup. Hurricane Katrina was way stronger than this storm. But Hurricane Katrina didn't undergo an extratropical transition, and New Orleans did not receive any snow from this storm. This storm, whether it's just known as the "Superstorm," the "Frankenstorm," "Sandy," or something else, is a meteorologists' fantasy. 

That being said, my heart goes out for everyone who is affected by this storm, whether they are riding it out on the East Coast, or they are praying for somebody else who is. Please stay safe.

One more thought... there are some fake photos going around. 

The theme seems to be various types of horrendous weather the Statue of Liberty. If you want the most accurate information and photos available, well, you know where to find it.


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