The relation between low latitude lightning activity and Forbush decreases (FDs) of galactic cosmic rays was studied, with flash rates observed by the Lightning Image Sensor aboard the Tropical Rainfall Measuring Mission satellite and FDs selected from the events with decreases more than 2% measured by the Mexico City neutron monitor. The effect of spacecraft precession on Lightning Image Sensor data complicates the analysis, but this can be dealt with by the approach we use. Applying a superposed epoch analysis to all of the 70 FD cases, we found the low latitude lightning activity decreases by about 10% after the Forbush minimum, with a 95% confidence level tested by Monte Carlo simulation, and recovers 3 days later. The response is more significant in the Southern Hemisphere. Our result provides evidence for a proposed link between solar activity, cosmic rays, the global atmospheric electric circuit, and cloud microphysics.