Hurricanes: A Primer for the Aviation Professional

This article has been written in response to the recent increase in hurricane activity within the Atlantic basin and the expectation that this heightened activity will continue for another 20 to 30 years. Its purpose is to educate aviation professionals on the hurricane phenomenon. The topics presented are focused, keying on information that will help these individuals better protect their aircraft and other resources. The issue of aircraft evacuation in response to a threatening hurricane is addressed throughout this paper. Introduction The number of hurricanes per season in the Atlantic basin, and therefore the potential for destruction fiom these storms, has shown a cyclical pattern with activity varying on the scale of decades. The period from the late 1920s through the 1960s was a time of relatively high activity in the Atlantic. Then activity decreased £torn about 1970 through the early 1990's (Goldenberg, Landsea, Metas-Nunez, and Gray, 2001). This region is now approximately ten years into another period of increased activity. This most recent period has been highlighted by many unusual events. This includes the record setting 2005 season in which there was an unprecedented occurrence of 28 named storms (NOAA News Online, April 13,2006). The unofficial record up until 2005 was 21 set in 1933 and the official record was 19 set in 1995, a year also within this latest period of heightened activity (NOMAOML, October 19, 2005). Given the historical pattern in stom frequency, the recent increase in activity is expected to last up to another 30 years. Aircraft are particularly vulnerable to the destructive force of these storms, especially those in the general aviation class. For example, when Charley moved through central Florida in August 2004 several a i r d in its path fiom Punta Gorda to Daytona Beach experienced signifcant damage (Anonymous, 2004/2005). When Wilma moved through south Florida in October 2005 both general aviation and larger jet transport aircraft were severely damaged at the Opa-locka Ahport (Boyd, 2006). Therefore, motivated by this recent increase in hurricane activity, the high probability that this period of high activity will persist, and the destructive impact these storms can have on aircraft this article has been written. My goal is to provide aviation professionals located along the hurricane prone East and Gulf Coasts of the United States with knowledge that will help them better protect their resources. Having an understanding of the humcane phenomenon is essential to making informed decisions on how to l i t the impacts of these storms. A basic but thorough understanding of the hurricane phenomenon is presented in this paper. This information will be focused, keying on those aspects of hurricanes that the decision maker in aviation needs to understand to better protect their JAAER, spring 2008 Page 55 1 Barry: Hurricanes: A Primer for the Aviation Professional Published by ERAU Scholarly Commons, 2008 Hurricanes: A Primer aircraft and other resources. One particular issue faced by the individual responsible for aircraft when a hurricane threatens is whether to evacuate their aircraft or stay put. This issue is an important part of this paper and is addressed throughout as we look at the hurricane phenomenon. Hurricanes: A Definition A hurricane is a surface low pressure center of tropical origin producing a distinct cyclonic (i.e., counter-clockwise) surface circulation that spirals m towards the storm's center. Surface wind speeds within a portion of the storm must be greater than 64 knots (74 mph) for the storm to be classified as a hurricane (Ahrens, 2003; NOANAOML, October 19, 2005). Note that the wind speeds reported with a hurricane or developing storm are sustained wind speeds (i.e., the average wind speed within a certain time period). The averaging period for winds reported with hurricanes is one minute. The implication of this is that wind speeds above the reported value (i.e., gusts) may also be present. If significant gusts are present, however, they are usually reported with the sustained wind speeds (NOAAIAOML, October 19,2005). An example of a hurricane as seen on a surface weather map is shown m Figure 1. This map shows surface conditions for 15 September 2004 at 18 UTC when Hurricane Ivan was approaching the Gulf Coast. The surface low pressure center and cyclonic circulation associated with Ivan is easily seen in this image. While this mean sea level pressure analysis indicates a central pressure somewhere between 988 and 992 mb, the central pressure of Ivan was in fact down to 937 mb at this time. This is a value 76 mb below the standard sea level pressure of 1013 mb. The maximum sustained wind speed that resulted from this "deep" low pressure center was 115 knots easily giving this storm hurricane status.