Tropical depressions and tropical storms are often more prolific lightning producers than hurricanes. However, the lightning produced by moderate-to-strong hurricanes usually occurs in preferred regions that may be important for hurricane intensity and precipitation nowcasting. Moderate-to-strong hurricanes typically produce periodic outbreaks of lightning near the eyewall, little lightning within the inner rain bands (or central dense overcast), and large amounts of lightning within outer rain bands.

Outbreaks of lightning within the eyewalls of moderate-to-strong hurricanes have been studied by Molinari et al. (1999). Molinari et al. (1999) found that outbreaks of eyewall lightning were generally caused by either eyewall contraction or secondary eyewall replacement. This means that eyewall lightning outbreaks may be able to help forecasters nowcast hurricane intensification (eyewall contraction) or weakening (secondary eyewall replacement). Molinari et al.'s (1999) work was limited to 5 Atlantic basin hurricanes where the center of circulation passed within 400 km of one of the U.S. National Lightning Detection Network (NLDN) sensors. In this study, we extend the work of Molinari et al. (1999) to include several category 3 or higher hurricanes as classified by the Saffir-Simpson Scale in both the Atlantic and Eastern Pacific basins from 2001 to 2003. Vaisala's VLF long-range lightning detection network has allowed the monitoring of lightning activity in hurricanes that are located many 1000's of kilometers from the nearest lightning detection sensor.

Molinari, J. P. Moore and V. Idone, 1999: Convective structure of hurricanes as revealed by lightning locations. Mon. Wea. Rev., 127, 520-534.