|Long Island Hurricane Climatology|
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An empirical study of 20 past hurricanes that have impacted the New York City and Long Island coast regions by Scheffner and Butler (1996) found that the return period of a category 3 or greater hurricane is approximately 80 years. A strong category 3 or minimal category 4 hurricane has a return frequency of approximately 200 years. (Click graph to the right for larger image.) Therefore, it is not unlikely that another "epic" hurricane will strike the Long Island coastal region in the coming decades.
|Research done by hurricane experts at the National Center for Atmospheric Research (NCAR) reveals that hurricane frequency in the Atlantic Ocean and Caribbean Sea regions runs on a 20-30 year cycle. (Time, 1998) The graphic to the left (Risk Prediction Initiative, 1998) clearly illustrates this cycle. The last intense period was in the 1950's and 1960's with a lag between 1970 and 1994. The hurricane frequency is on the upswing once again which increases the chances for landfall everywhere along the east coast of the U.S.|
|Unfortunately, in the past few decades, the coastal population has also increased substantially which further increases the hurricane risk. Even though more sophisticated forecasting tools such as satellites and Doppler radar are providing more lead-time for issuing warnings, the threat of massive deaths remains fairly high due to the increased coastal populations.
Source: USGS, 1998
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Source: Time Magazine, 1998
The tables to the right show probability estimates for the occurrence of various disaster events (including hurricanes) that could impact the U.S. in the future. While it may not be surprising to see that there is a >99% likelihood of at least 10 deaths from a hurricane in the next 10 years, it should be noted that the data indicates a 71% probability of 1,000 deaths from a hurricane in the next 20 years!
Climate Change and Hurricanes:
A recent paper published by some of the top hurricane researchers in the field (Knutson, et al. 2010) concludes:
...future projections based on theory and high-resolution dynamical models consistently indicate that greenhouse warming will cause the globally averaged intensity of tropical cyclones to shift towards stronger storms, with intensity increases of 211% by 2100. Existing modelling studies also consistently project decreases in the globally averaged frequency of tropical cyclones, by 634%. Balanced against this, higher resolution modelling studies typically project substantial increases in the frequency of the most intense cyclones, and increases of the order of 20% in the precipitation rate within 100 km of the storm centre.
There has been an observed increase in tropical cyclones (TC) since the mid-1990s. Warmer oceans have played a significant role in this increased frequency. A new study by Emanuel (2010) suggests that lower stratospheric cooling may also be responsible for the uptick in activity and intensity. Climate models may be underestimating future hurricane frequency and intensity because they do not appear to include the impact of stratospheric cooling. Emanuel's research suggests that there may be more hurricanes in the future despite the current consensus of a 634% decrease in frequency.
By 2100, the climate is expected to warm 5 oC to 6 oC or more above pre-IR values. During the Pliocene, about 2.5 to 5 million years ago, CO2 levels were comparable to today's levels (near 400 ppm) and the climate was about 3 oC to 5 oC warmer than pre-IR. Geographically, the Earth was also very similar to today so the Pliocene offers a glimpse of what the world may look like by the year 2100. Federov, Brierley, & Emanuel (2010) modeled the expected TC activity in the early Pliocene world. Fig. 29a (Ibid) is a comparison of modern TC activity (a) and that of the Pliocene (b). This image is a sobering look at what may lie ahead in our world by 2100.
Vechi, Swanson, and Soden (2008) conclude that predicting the future of hurricane activity is at a crossroads. Vechi et al. compared the observed relation of the power dissipation index (PDI) vs. sea-surface temperatures (SST) in the main development region of Atalntic hurricanes. (PDI is the cube of the instantaneous tropical cyclone wind speed integrated over the life of all storms in a given season; more intense and frequent basinwide hurricane activity lead to higher PDI values.) There are two very different futures depending on whether absolute SST or relative SST controls PDI.
Figure 29b (ibid) shows PDI anomolies based on absolute SST.
By 2100, the lower end of the model projections shows a PDI comparable to that of 2005, when four major hurricanes (sustained winds of over 100 knots) struck the continental United States, causing more than $100 billion in damage. The upper end of the projections exceeds 2005 levels by more than a factor of two. Combined with rising sea levels, coastal communities face a bleak future if absolute SST determines hurricane activity and strength.
Figure 29c (ibid) shows PDI anomolies based on "relative SST" which is the SST in the tropical Atlantic main development region relative to the tropical mean SST.
A future where relative SST controls Atlantic hurricane activity is a future similar to the recent past, with periods of higher and lower hurricane activity relative to present-day conditions due to natural climate variability, but with little long-term trend.
Because the correlation of PDI vs. absolute SST and PDI vs. relative SST are equivalent, Vechi et al. conclude that more research is needed in this area.
Realclimate's Atlantic Tropical Cyclone Records Trends and Ephemerality (June, 2010) is a very good synopsis of what is known and not known about climate change and tropical cyclone projections.
Around Halloween 2012, Hurricane/Superstorm Sandy battered the east coast and especially the New York City metro region with record high storm surge levels that flooded tunnels and subways, and destroyed tens of thousands of homes and businesses. Sandy's hurricane force winds downed trees and power lines that left millions without power for more than a week. Please see my two blog posts Global Warming Made Hurricane Sandy Worse and 71,000 New Yorkers: Rise Does Matter! for information about the link between climate change and this epic storm.
The next section deals the future threat of New York hurricanes and some worst-case scenario simulations of older events.
|Scott A. Mandia, Professor -
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