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Article | Summer 2007

The Cone of Uncertainty and Hurricane Forecasting

Cone of Uncertainty: Hurricane Charley 2007 is predicted to be a busy hurricane season. Scientists say last year's El Nino kept strong storms in check, but this year, we may see La NiÃ±a developing, bringing with it a bigger chance of hurricanes. How will the millions of people living near coastlines in the southeastern United States react to hurricane forecasts presented this year?

According to researchers from the Center for Research on Environmental Decisions(CRED), the manner in which weather forecasts are presented is critically important to risk management. Their recent study, published in the May 2007 issue of the Bulletin of the American Meteorological Society (BAMS), examined the "cone of uncertainty," a visual aid used by the National Hurricane Center and often adopted and adapted by the media to communicate hurricane risk to the public prior to landfall. Research indicates that this forecast product is subject to misinterpretation by generalists and specialists alike, with serious consequences. Misinterpreting consequences of intense storm warnings can have much more dangerous consequences than misinterpreting a daily weather forecast, where a 20% chance of rain can be interpreted in numerous ways (e.g., 20% chance of just one drop of rain falling, rain over 20% of a specified area, rainfall for 20% of the forecast period).

The "cone of uncertainty"-also known colloquially as the "cone of death," "cone of probability," and "cone of error"-represents the forecasted track of the center of a tropical storm or hurricane and the likely error in the forecast track based on predictive skill of past years as well as numerous additional details about the storm (see Figure 1). Kenneth Broad, a cultural anthropologist at the University of Miami, Tony Leiserowitz, a geographer at Yale University, and colleagues took a closer look at the factors likely to contribute to the misunderstanding of this visual device for conveying hurricane warnings. Broad is a Co-Director of and Leiserowitz a Senior Investigator with CRED, which studies how people make decisions under environmental risk and climate uncertainty.

They conducted a newspaper content analysis, interviewed government and television meteorologists, undertook an event analysis of the 2004 Hurricane Charley, and reviewed third party surveys to identify the primary factors leading to misperception of the "cone of uncertainty." The primary conclusion is that people put too much faith in the track line forecast, negating the uncertainty message that the cone is intended to convey. Additionally, there is confusion about what the cone represents. Many believe that it depicts the potential swath of destruction of the storm while in reality, it only represents the potential area the center ("the eye") of the storm may travel in. Over the past decade, storms have traveled within the cone about two-thirds of the time. Broad and Leiserowitz also concluded that the hurricane warning packs too much information into a single graphic, confusing the recipient and causing difficulty in pulling out the most relevant bits of information.

There is no perfect "one size fits all" image, given the range of vulnerabilities and potential responses of a socio-economically and culturally diverse population in the southeastern United States. Many factors influence risk perception and decisionmaking, including the nature of the risk, the trustworthiness and credibility of the messenger, the knowledge, values, and worldviews of the recipient, and so on. Thus, the utility of any single risk communication product must be evaluated within the individual, social, and institutional contexts of the recipient. What to include and not include should reflect who the intended audience is and their ability to handle different sorts of information.

It is critical that producers of information focus on the relevance of the information and whether it provides enough detail for particular decisionmakers to assess their own risks. For example, some individuals and areas are more vulnerable to storm surge (coastlines), others to wind speed (trailer parks), and others to the loss of electricity (e.g., those who rely on refrigerated medication). Merely knowing the likelihood that a hurricane might strike a particular area does not provide the more specific information people need to consider when assessing the risks and choosing a course of action.

The communication of hurricane risks is an essential function of both government and the private sector. Decisionmakers at all levels, from individuals to institutions, now rely, at least in part, on these messages to make critical decisions about hurricane preparedness and evacuation. The "cone of uncertainty" has quickly become a key device for the communication of hurricane risks; yet we still know relatively little about how audiences actually interpret, evaluate, or utilize this key graphic. Social science methods and approaches should be integrated into the design, development, and evaluation of hurricane risk communications, so vital for the wellbeing of the public.