Moderate and Higher Cloud to Ground Lightning Within Tropical Cyclone Feeder Bands on the Florida Peninsula

An aspect of tropical cyclone activity that has to be accounted for is the lightning strikes they produce within their outer feeder bands and the state of Florida is a leader for both in the United States. Identifying the conditions favorable for moderate and higher cloud to ground lightning strikes can mitigate some of the risk utilities face when dealing with the many hazards tropical cyclones provide. These moderate and higher cloud to ground lightning densities are defined as a minimum of 76 lightning strikes in a 5 X 5 km grid space over 1 hour of time. As an adjunct part of the broader Florida Thunderstorm Index, a meteorological examination of how these impactful lightning storms have occurred is the main subject of this paper. Often these feeder band thunderstorms run counter to the broader averages of moisture and instability based on their steering flows that thunderstorms driven by other micro, meso and synoptic scale patterns bring about (Smith, 2015). Moderate or higher lightning storms in feeder bands can impact areas beyond the bounds of hurricane and tropical storm advisory areas as well as ahead of and after any issuance. While utilities prepare for wind and flooding, lightning strikes can add additional resources straining native and mutual assistant crews. Often these feeder band thunderstorms happen hundreds of miles away from the center of a tropical cyclone circulation and many times in the formative stages of a tropical cyclone. A common thought is that tropical depressions, tropical storms and hurricanes do not produce much lightning and while that may be true compared to sea breeze thunderstorms in Florida, this hazard cannot be discounted and must be part of a utilities assessment plan before an imminent tropical system gets named and also days later during the restoration process. The data analyzed for this paper compiles steering flow, moisture content and instability levels within tropical cyclones that have impacted Schneider Electric's Florida energy clients from 2007-2014. This period was especially noted as one that did not see a single hurricane make landfall in Florida yet from nearly each tropical system that impacted the peninsula, moderate and higher lightning storms from outer bands occurred. The paper also looks into the tracks of these tropical cyclones determining which tracks produced the greater density of lightning relative to location in Florida. Some of these thunderstorms occurred just prior to a system being classified a tropical cyclone and were also analyzed. Disruptions to utilities have occurred with these feeder band thunderstorms though the discrepancy between whether it was lightning and/or other factors such as the winds are difficult to ascertain. Nevertheless, while a “hidden danger” in the public due to tropical cyclones is the flooding, to utilities this may be in the form of higher lightning strikes which like the rise in water can have far reaching impacts.