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The meteorology behind Hurricane Sandy’s very low pressure

Nearly three years since Hurricane Sandy, many of her visual scars have faded. The memories of the storm, for many, have not. Meteorologically, Sandy remains just as incredible now as she was then — an unbelievable display of atmospheric power. One of the most fascinating aspects of Sandy was how strong she was, despite entering cooler waters. The meteorology behind her pressure is powerful and intricate, still, three years later.

Hurricanes have a strong warm core at the surface, weaken with height, and are barotropic — meaning there are no temperature or density gradients in their environment. This means that they are symmetric — their warm core is entirely surrounded by slightly cooler, but still abundantly warm air. The combination leads to hurricanes being vertically stacked (not tilted with height). Thus, hurricanes need warm water and weak upper-level winds in order to strengthen. Strong upper-level winds can choke a hurricane’s outflow channel, and advect in new airmasses of different temperatures — providing temperature gradients that hinder their development.

In further south latitudes, waters tend to be warmer, and the jet stream tends to be weak. As you head further north, however, the water becomes colder and the jet stream strengthens, leading to stronger upper-level winds. This helps to weaken a hurricane’s warm core at the surface, and tilt its vertically stacked structure, weakening the storm. However, as Sandy headed north, she was able to maintain category one hurricane strength with abnormally low pressures and eventually went on to cause widespread devastation. Why?

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Hurricane Sandy in 10 shocking images

One year ago today, Hurricane Sandy made landfall on the New Jersey Coast. The storm, although well predicted several days in advance, caused billions of dollars in damage as well as significant loss of life and property. In addition to our Hurricane Sandy Anniversary Archive, our forecasters have chosen ten of the most shocking images that still remain incredible a year later — showing the size, strength and impact of Sandy in our area.

Hurricane Sandy, and her curiously low pressure

One of the most fascinating aspects of Sandy was how strong she was, despite entering cooler waters. Hurricanes have a strong warm core at the surface, weaken with height, and are barotropic — meaning there are no temperature or density gradients in their environment. This means that they are symmetric — their warm core is entirely surrounded by slightly cooler, but still abundantly warm air. The combination leads to them being vertically stacked (not tilted with height). Thus, hurricanes need warm water and weak upper-level winds in order to strengthen. Strong upper-level winds can choke a hurricane’s outflow channel, and advect new airmasses of different temperatures — providing temperature gradients that hinder their development. In further south latitudes, waters tend to be warmer, and the jet stream tends to be weak. As you head further north, however, the water becomes colder and the jet stream strengthens, leading to stronger upper-level winds. This helps to weaken a hurricane’s warm core at the surface, and tilt its vertically stacked structure, weakening the storm. However, as Sandy headed north, she was able to maintain category one hurricane strength with abnormally low pressures and eventually went on to cause widespread devastation. Why?

Sandy was able to maintain strength and deepen as she became a hybrid of a tropical low and an extratropical low. Strong extratropical lows, such as nor’easters, have cold cores at the surface. Instead of being vertically stacked, they tilted towards cold air with height. This means that they are baroclinic; thermal and density gradients exist in their environment, including frontal systems. More specifically, they are asymmetric — with cold air on the west side of the circulation, and warm air on the east side (by definition, a temperature gradient). Sandy was a hybrid in that she had a warm core of strong winds, but was also asymmetrical, meaning her strength was aided by strong upper-level winds and thermal gradients, instead of being hindered by them.

The large trough that phased with and turned Sandy to the west had an abundant source of cold air and strong upper-level winds. There were actually reports of 2-3 feet of snow in West Virginia! That cold air was able to clash with the warmer, tropical air, creating a steep thermal gradient, helping Sandy’s pressures to deepen, despite heading towards colder waters. Additionally, there were several sources of strong upper-level winds that were all co-located in a perfect position for serious strengthening. When forecasters saw these localized areas of strong upper-level winds (also called jet streaks), it was pretty evident that the model solutions which took Sandy to pressures around 940mb at landfall were not off the wall, and were very much possible.

A GFS forecast showed that Sandy was located in the presence of four different jet steaks -- each one favoring a strengthening storm.

A GFS forecast showed that Sandy was located in the presence of four different jet steaks — each one favoring a strengthening storm. Sandy is denoted with the circle and the “S” inside. The jet streak regions are drawn and labeled as well.

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Cleanup Begins After Sandy Hammers Area

Hurricane Sandy slammed into the New Jersey Coast near Atlantic City last night, and brought a ferocity rarely seen from storms systems in this part of the country. The storm was near a record low pressure at landfall at landfall, and the track and intensity brought severe hurricane force winds, heavy rain, beach erosion, historical damaging coastal flooding and storm surge. As the cleanup continues, we step aside but also answer some questions you may have remaining and analyze several pieces of the storm.

Storm Surge: The storm surge began early Monday in Central New Jersey as Sandy was still hundreds of miles southeast of the area. By later Monday, the surge was rapidly pushing sea water into the streets of coastal cities such as Atlantic City, Ocean City, Long Beach Island, and Long Branch. The waters continued to flood into Tuesday morning up and down the New Jersey shore.

Historical storm surge occurred after the system made landfall, as high tide juxtaposed with hurricane force southeast gales. This pushed a wall of water into the south shores of Long Island and New York Harbor. Record storm tide levels were reached at The Battery, where the water reached nearly 14 feet. The previous record stood at 10.1 feet. The surge in the Hudson and East rivers sent water pouring into the streets of mid and lower manhattan. The rivers also spilled into Jersey City and Hoboken. Significant flooding was observed in the subway stations near and underneath the East River. The subway system may inoperable for weeks.

The southeasterly gales also brought a wall of water to the south facing shores of Long Island, Long Beach, the Rockaways, South Brooklyn, as well as many other locations which saw the water pour into the streets from the beach.

Winds: Hurricane force wind gusts were widespread throughout the area — almost everyone experienced them at some point. Arguably the strongest winds occurred after the system was near landfall, as mixing improved in the low levels of the atmosphere with cold air advection beginning as the system transitioned to post tropical. This was a disaster waiting to happen, as strong winds were ripping just above the surface and could not more effectively mix down to the surface. Gusts of near 90 miles per hour were reported at many official stations in the NYC Area — unprecedented.

The winds downed thousands of trees in towns and transformers were seen flashing in the sky, exploding as trees and branches fell on power lines and winds continued. The winds also attributed to what will eventually be seen as one of the most severe beach erosion episodes in history.

We compiled as list of some of the highest wind gusts in the area:

Eatons Neck, LI – 96 mph
Islip – 90 mph
Montclair- 88 mph
Madison (New Haven) – 86 mph
Kennedy Airport – 79 mph
La Guardia Airport – 74 mph
Central Park – 62 mph

Flooding Rain: The flooding rain was not as much of an issue over Northern NJ and NYC as it was over Southwestern New Jersey. The flooding (rain aside) was tremendous in response to the aforementioned storm surge and winds. Thousands of homes are destroyed, millions are without power.

Was this storm everything we expected it to be? Yes, and the damage more than we thought it would be. The storm was historic in many aspects — and the billion dollars of damage it caused, and effect it had on people’s lives, is remarkable

Will we see something like this again? Not likely for a very, very long time. The storm you just witnessed was a once in a century type storm. It required a specific set of events to go completely according to plan in exact order, and certain atmospheric variables needed to be perfectly in place. As a meteorologist, watching this unfold was truly remarkable and humbling. But most importantly, I hope that in disseminating the information we did, that we helped to keep you informed and prepared..and hopefully saved lives.

To all affected, wish you all the best.