With the U.S. coasts now subject to frequent landfalling hurricanes, this may seem like the new normal. Over the last 250 years, during the late 19th and early 20th centuries, these killer storm systems wreaked havoc on cities and towns across America.
According to the National Hurricane Center’s Historical Data Library, more than 39,000 U.S. people were killed and over $67 billion in the insured property was destroyed in 124 U.S. hurricanes from 1900 to 2017. This includes Superstorm Sandy in 2012, which caused a third of this total figure.
Surviving a devastating hurricane requires planning and preparation, with a series of events from ignition to recovery that must be managed. Although we have multiple ways of assessing and reporting these types of events, the ability to conduct this analysis has been limited.
The earliest known data on the frequency of a hurricane striking a particular American city comes from the New Madrid Severe Pile-Up of 1893. The Irish Met Office’s records of frequent tornadoes in the American Midwest weren’t as accurate for six decades, as the infrastructure there was still insufficient to detect and convey information to government entities. At the end of the 20th century, the first detailed hurricane database for the United States began to accumulate.
A Storm on the Same Scale as Superstorm Sandy.
Between 1900 and 1893, 15 hurricanes struck the American coastal states of Maine, Massachusetts, and Vermont, while 13 hit the East Coast and Gulf of Mexico coasts. Seven hurricanes struck in 1916 and seven struck again in 1916. After the storms in 1916, so many homes were toppled in New York City that the death toll alone amounted to 30,000 and almost as many in Philadelphia.
In the 1940s, researchers were able to identify the Category 1 and 2 storms that were produced by “wedge-shaped” cyclones. Category 1 hurricanes had winds of at least 111 mph, while Category 2 hurricanes had winds of 115 mph or higher. By 1950, computers were able to quickly calculate how many fatalities and damages were caused by each hurricane.
However, the power of these storms had obscured the fact that they were less destructive and far less frequent than what scientists were now learning of. To gain more insight into the effectiveness of the old hurricane index, researchers were able to extract the probability of a hurricane hitting an area from a computer simulation. The study defined a Category 1 hurricane as a storm with winds of at least 90 mph, while a Category 2 hurricane had winds of at least 110 mph. These estimates are conservative and do not take into account the damage caused by high winds.
The research found that in the United States, before World War II, it was highly unusual for a Category 1 hurricane to strike. It continued for 10 years after the war. However, there was also significant variability in the frequency of Category 1 and 2 hurricanes, even after World War II. Researchers believe that both fluctuations and luck may have helped to account for this variability.
Storms from 1915 to 1966 yielded seasonal information that was not very useful because the storms occurred on very different timescales. In fact, the storm activity from 1916 to 1966 was so similar in several parts of the United States, where the storm wasn’t strong enough to produce large property damage and death, that researchers couldn’t say if there was any correlation.
Hurricane Frequency Change By Level Of Strength (L to S) in the American Coastal States, 1900-2018.
A quick look at the southern U.S. coast reveals more patterns of variability in the frequency of Category 1 and 2 hurricanes. The hardest-hit part of Florida, the Florida Keys, had an average chance of being struck by a Category 1 hurricane every 4 years. From 1961 to 1965, the number of Category 1 hurricanes that struck Florida nearly doubled in the three-year period. But from 1969 to 1975, that number dropped significantly. Meanwhile, the home state of hurricane relief, Mississippi, has had an average of one Category 1 hurricane every five years.
These charts of the life cycle of tropical storms and hurricanes provide a unique comparison to other types of extreme weather. Loss of life, costs of damage, and physical damage are just a few examples of the impacts that hurricanes can have, even if it is 10, 20, or 30 years later that these impacts are finally assessed. In response to this trend, the U.S. Geological Survey, National Oceanic and Atmospheric Administration, and the American Meteorological Society began working on a new systematic database to gather and evaluate current hurricane data.
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