The incredible storm affecting much of the US eastern seaboard and its huge population may have a long lasting impact. And many experts have stated that this so called “Frankenstorm” will have been the strongest storm residents of the east have ever seen- a storm without precedent. It certainly is potentially deadly and will wreak destruction from coastal storm surge, damaging winds and intense rainfall. But without precedent? Let me place this storm in its proper perspective.
As meteorologists, we tend to categorize extreme weather events by calculating what their “return frequency” is. That is, how often a storm of this magnitude might be expected to occur. Every 50 years, or every 100 years? Every 500 years? There are a variety of statistical methods that can help us arrive at these numbers to better define how rare an event is. And SuperStorm 2012 can thus be statistically understood. But there have been other events during this time of year, in that part of the country, which can be cited immediately, that have brought similar weather threats and hazards.
A little over 20 years ago, a category 2 hurricane named Grace was moving northeast near the North Carolina coast and interacted with a cold storm coming off the mainland. In October of 1991, the Perfect Storm developed causing hurricane force winds in areas off New England with extensive coastal erosion. The system ultimately sank the Andrea Gail, a fishing vessel returning to harbor in Gloucester, Massachusetts on October 28, 1991. A book was written about this event, and a movie was produced in 2000. The Perfect Storm caused over $200 million damage and killed 13 people.
There are striking similarities between SuperStorm 2012 and the Perfect Storm. The primary difference is that the 1991 event came together about 300 miles farther east out to sea. Today, Frankenstorm is strengthening while moving in from the southeast to impact the New Jersey coastline Monday evening. Both systems were hybrid, bringing immense meteorological potential from tropical and polar sources.
Tropical cyclones derive their wind power from warm sea surface temperatures that convert the heat energy into intense thunderstorms around a tight core, or eye. Polar (extratropical) cyclones derive their wind power from temperature changes around the storm. Technically, this is known as baroclinicity. But it simply means an environment where winds are blowing colder air from one area to another. The infusion of colder air into a polar cyclone strengthens it. And so, when you bring the best of both types of cyclones together you are likely to get a whopper- a monster zone of low pressure.
Tropical systems bring unique hazards, such as a rising sea level right along the coastline. This is due to physical forcing of the water ahead and to the right of the storm center combined with the lower atmospheric pressure allowing for rising water levels (since the weight of the air pushing down on the water lessens). Polar systems bring unique hazards too, such as a broad wind field. While hurricanes have their strongest winds wrapped around a relatively small eye wall, polar lows have high winds spread out for hundreds of miles in all directions. All of these elements will be plaguing the eastern seaboard for days.
Back in October of 1938, the Great Hurricane of ’38 hit New England. It was also known as the Yankee Clipper and the Long Island Express. This was a full-fledged hurricane as it blew up straight from the south, crossing the middle of Long Island on September 21st of that year. It had been a category 5 hurricane earlier and stuck the US coastline as a category 3. This system caused over $306 million damage, destroyed more than 50,000 homes and killed nearly 800 people. In 2012 dollars the damage would equate to $4.7 billion.
On August 24, 1893 New York City was directly hit by the New York Hurricane. This was a former category 3 storm that struck the city and western Long Island as a 110 mph category 2 system. There was extensive damage.
During early October of 1869, more than 100 people were killed by the “Saxby Gale”, a category 2 hybrid hurricane/polar cyclone that hit New England.
On September 2nd and 3rd, 1821 the east coast was devastated by a monster category 4 hurricane. This huge storm, also known as the “Norfolk and Long Island Hurricane” with 135 mph sustained winds roared northward from coastal North Carolina through the Tidewater of Virginia, up through Delaware Bay and Philadelphia, then over New York and up through New England. Manhattan saw a storm surge of 13 feet, the greatest ever in New York. There were only about 25 confirmed deaths (many more suspected) and a damage estimate of $200,000. Of course, that same storm taking the same track today would be much more destructive than Frankenstorm is expected to be.
Finally, the Great Colonial Hurricane of 1635 rammed onshore on August 25th of that year. Tremendous impact was felt from the Jamestown colony in Virginia up through New Amsterdam (today’s New York) to Plymouth Colony. This event has been reconstructed as a strong category 4 hurricane. The storm surge into Rhode Island was 22 feet, the strongest ever measured.
Frankenstorm will no doubt hit hard. But storms like this will strike the eastern seaboard roughly once every 75 to 100 years. Frequency of such events is fairly consistent. However, a big change in the equation is population concentration. In the west, Los Angeles always has and always will deal with issues to supply multi millions of people potable water in a desert. So too, increased development in areas prone to hurricanes or Frankenstorms will not lessen the climatological return frequency of these storms. It will only increase the necessity to prepare for what is ultimately inevitable. Perhaps that is the biggest challenge.