Thar She Blows
September 07, 2011
Sarah Oktay, PhD, Managing Director UMass Boston Nantucket Field Station
Honestly I would rather be writing about a giant white sperm whale. At the moment, I am sitting in a hotel in Hubbard, Ohio (very close to the border of Pennsylvania) and will hit the road in a couple of hours to get back to Nantucket for the UMass Boston Nantucket Field Station Open House. It’ll be a great event with guest scientists from around the region and lemonade and cookies for 300+ people.
What’s between me and my final destination, and why I am driving when I had perfectly good airline tickets? Well, every eastern city’s airport has been shut down due to a storm that grew to be the size of Europe as it raced up the Atlantic Coast. Hurricane Irene has barreled through and although it could have been a much stronger and more devastating hurricane, it has been an unprecedented storm in many ways. Mayor Michael Bloomberg evacuated a large portion of New York City for the first time in the days leading up to the storm. Many states including those as far north as Vermont have taken unexpected hits due to the rain disgorged by huge multiple bands of thunderstorms from the spin art effect of the cyclonic storm. The storm brought torrential rains and powerful winds, stretching 300 miles from the center at one point and was frequently described as “the size of Europe” in various news media outlets. Few storms in recent memory have affected such a large swath of the heavily populated coast. We are much better off than many parts of the country, not the least of which is North Carolinas “Outer Banks.” The lone road connecting the Outer Banks to the mainland was washed out, making it difficult for emergency crews to access those on island with supplies and assistance. About 2,500 people on Hatteras Island were cut off from the mainland, and authorities sent a ferry Sunday August 28th full of supply trucks carrying food, water and generators.
Although the Hurricane Season in New England begins on June 1, August and September are the prime months. Most of the 40 tropical systems that have hit over the past century have been in those months. Once a named hurricane causes significant damage; that name is retired. Hurricanes that produced massive rain or wind and storm surge damage to Massachusetts over the past 200 years include: Bob, Diane, Donna, Edna, Gloria, “Dog” (great name—probably after a labradoodle), Carol, the infamous “Long Island Express,” “The September Gale (1869), the “Great September Gale” (1815), and a couple of others. Here is a link to a short but useful review of the major hurricanes that have made their way to our neck of the woods: http://www.wickedlocal.com/nantucket/news/environment/x832281924/The-dirty-dozen-of-New-England-hurricanes#axzz1WVIHdglF. That is not very many storms in such a long stretch of years, and we’ll see soon that many storms originating down south get torn to pieces or degraded by sheer with land or a collision with cold air masses before they get too far up here. In fact, the September 23, 1815 (the “Great September Gale” mentioned above) was the first major hurricane to impact New England in 180 years.
Nantucket Island is in relatively good shape, with early warnings and storm prep and haul out of boats preventing major damage to property. As is often the case in storms like this, the beach between Miacomet Pond and the ocean has been breached, and south shore erosion and riptides are significant. Fortunately for New Englanders, colder water and the sheering force of the storm grinding against the Atlantic coast weaken the majority of storms before they can do too much damage. The two most significant hurricanes to hit Nantucket over the past 30 years were Hurricane Bob and the “No Name” storm which assaulted the island in August and October of 1991 respectively. The No-Name Storm, as those who have enjoyed the book by Sebastian Junger or the movie (The Perfect Storm) know, formed as a low pressure system built up over Canada, a high pressure system extended from the Gulf of Mexico northeastward, and Hurricane Grace formed off the coast of Florida and moved north, all combining together into what is commonly .kown as “a perfect storm.” If you have the chance, go to the Shipwreck and Lifesaving Museum, our neighbors on the other side of Folgers Marsh at 158 Polpis Road to see the 20th anniversary exhibit of “Storm Stories! 1991: An Island Remembers” to learn more about these storms which are still seared in most islanders memory. At the Field Station, we have a very high water mark 2 feet above the ground level on our office building from the storm surge from Hurricane Bob.
The National Hurricane Center (via the National Oceanic and Atmospheric Administration) is the best place to find comprehensive information about hurricanes. The terms "hurricane" and "typhoon" are regionally specific names for a strong "tropical cyclone." Here is a definition of tropical cyclones from the Atlantic Oceanographic and Meteorological Research Lab (http://www.aoml.noaa.gov/hrd/tcfaq/A1.html) contributed by the extremely aptly named, Chris Landsea; “A tropical cyclone is the generic term for a non-frontal synoptic scale low-pressure system over tropical or sub-tropical waters with organized convection (i.e. thunderstorm activity) and definite cyclonic surface wind circulation. Tropical cyclones with maximum sustained surface winds of less than 17 m/s (34 kt, 39 mph) are usually called "tropical depressions." Once the tropical cyclone reaches winds of at least 17 m/s (34 kt, 39 mph) they are typically called a "tropical storm" or in Australia a Category 1 cyclone and are assigned a name. If winds reach 33 m/s (64 kt, 74 mph), then they are called a "hurricane" (in the North Atlantic Ocean, the Northeast Pacific Ocean east of the dateline, or the South Pacific Ocean east of 160E) or a "typhoon" (in the Northwest Pacific Ocean west of the dateline). In the southerly oceans they are known as "severe tropical cyclone" or "Category 3 cyclone" and above ( referring to the Southwest Pacific Ocean west of 160°E or Southeast Indian Ocean east of 90°E), a "very severe cyclonic storm" (the North Indian Ocean) or just a "tropical cyclone" (the Southwest Indian Ocean- apparently into understatements there). In other words, a tropical cyclone is a storm system characterized by a low pressure center and numerous thunderstorms that produce strong winds and flooding rain. A tropical cyclone feeds on heat released when moist air rises, resulting in condensation of water vapor contained in the moist air. They are fueled by a different heat mechanism than other cyclonic windstorms such as nor'easters, European windstorms, and polar lows, leading to their classification as "warm core" storm systems.
Cyclones are areas of closed, circular fluid motion rotating in the same direction as the Earth. This is usually characterized by inward spiraling winds that rotate counter clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere of the Earth. There are a number of structural characteristics common to all cyclones. As they are low pressure areas, their center is the area of lowest atmospheric pressure in the region, often known in mature tropical cyclones as the eye. Near the center, the pressure gradient force (from the pressure in the center of the cyclone compared to the pressure outside the cyclone) and the Coriolis force must be in an approximate balance, or the cyclone would collapse on itself as a result of the difference in pressure. The wind flow around a large cyclone is counterclockwise in the northern hemisphere and clockwise in the southern hemisphere as a result of the Coriolis effect. (An anticyclone, on the other hand, rotates clockwise in the northern hemisphere, and counterclockwise in the southern hemisphere.) The largest low-pressure systems are cold-core polar cyclones and extratropical cyclones which lie on the synoptic scale. A synoptic scale is simply a size or horizontal length of the order of 1000 kilometers or 620 miles on the planet (layman’s terms, dang, that’s big!). Warm-core cyclones such as tropical cyclones, mesocyclones, and polar lows lie within the smaller mesoscale (meteorology talk for smaller). Subtropical cyclones are of intermediate size. Upper level cyclones can exist without the presence of a surface low, and can pinch off from the base of the Tropical Upper Tropospheric Trough during the summer months in the Northern Hemisphere (sounds painful—basically means upper level cyclones that don’t interact much with the ground). Cyclones have also been seen on extraterrestrial planets, such as Mars and Neptune. (from http://en.wikipedia.org/wiki/Cyclone).
The term "tropical" refers to both the geographic origin of these systems, which form almost exclusively in tropical regions of the globe, and their formation in Maritime Tropical air masses. The term "cyclone" refers to such storms' cyclonic nature, with counterclockwise rotation in the Northern Hemisphere and clockwise rotation in the Southern Hemisphere. The term cyclone means “Coiled Snake” in Greek and was coined by British East India Company official Henry Piddington in 1848 to describe the devastating storm of December 1789 in Coringa, India. It has been applied to tornados from 1856.
While tropical cyclones can produce extremely powerful winds and torrential rain, they are also able to produce high waves and damaging storm surge. They develop over large bodies of warm water, and lose their strength if they move over land. This is the reason coastal regions can receive significant damage from a tropical cyclone, while inland regions are relatively safe from receiving strong winds. Heavy rains, however, can produce significant flooding inland, and storm surges can produce extensive coastal flooding up to 40 kilometers (25 mi) from the coastline. Although their effects on human populations can be devastating, tropical cyclones can also relieve drought conditions. They also carry heat and energy away from the tropics and transport it toward temperate latitudes, which makes them an important part of the global atmospheric circulation mechanism. As a result, tropical cyclones help to maintain equilibrium in the Earth's troposphere.
Scientists are looking at how climate change and our warmer sea surface temperatures might be affecting hurricanes by examining their frequency and strength over time. More energy in the system from warmer water (which is very well documented) may mean that we have to endure more dissipation of this energy in the form of more frequent or slightly stronger storms. In fact, hurricanes do have a silver lining. In some areas like the Gulf coast, they can help to flush out contaminated harbors. Sediment layers in a coastal area will typically have an obvious “hurricane” layer where discontinuities in the deposition are observed.
The hurricane formerly known as Earl that was downgraded to a tropical storm by the time it hit Nantucket last year on Labor Day weekend was the most recent cyclonic storm to hit Nantucket. The last time the Cape was hit directly by a hurricane was 1991, when Bob brought 75 mph gusts that ripped through the region's grassy dunes, snapped trees and tore roofs off gray shingled homes. The “No Name Storm” was not an “official” hurricane and you can learn more about why it was not originally named and how it formed at http://perfectstorm.warnerbros.com/cmp/thestorm.html.
If you want to learn about global cyclones from how they are tracked to risk analysis and trivia check out this series of articles: Holland, G.J. (1993): "Ready Reckoner" - Chapter 9, Global Guide to Tropical Cyclone Forecasting, WMO/TC-No. 560, Report No. TCP-31, World Meteorological Organization; Geneva, Switzerland - cawcr.gov.au/bmrc/pubs/tcguide/ch9/ch9_9.htm.
I got the following information on terms associated with hurricanes from the Chapter above:
Typhoon = Big Wind: The derivative of the word typhoon seems to have arisen from very appropriate Mandarin word t'ai fung for great wind.
Hurricane = Angry God: The derivative of the word hurricane comes from Huracan, or "God of Evil" used by the Central American Tainos tribe.
Clement Wragge, the Australian forecaster who started the convention of naming tropical cyclones, occasionally named a particularly severe one after politicians with whom he was displeased.
According to the New York Times, Hurricane Irene’s repair cost will be at least 7 billion dollars, making it one of the most expensive storms to date. “At $7 billion in possible losses, Irene would be among the 10 costliest catastrophes in American history, according to the Insurance Information Institute. The most expensive disaster by far was Hurricane Katrina in 2005, which caused $45 billion worth of damage, not counting costs that were covered by the National Flood Insurance Program. The second, at about $23 billion, was the Sept. 11, 2001, terrorist attacks on the World Trade Center and Pentagon, which the institute counts as a single event. All but one of the remaining top 10 were hurricanes, ranging in cost from $22 billion for Hurricane Andrew in 1992 to $6 billion for Hurricane Rita in 2005.” Some estimates put the toll closer to 1 billion and it will most likely be several weeks before we know the true extent of the damage. National Guard crews are augmenting state and local police, fire, FEMA, and other emergency responders around the nation.
Here’s hoping you and yours are safe and sound and enjoying the cool and sunny aftermath.