https://phys.org/news/2018-08-nasa-tropical-storm-john.html

On Aug. 6 at 4:40 a.m. EDT (0840 UTC) the Moderate Resolution Imaging Spectroradiometer or MODIS instrument aboard NASA's Terra satellite analyzed Tropical Storm John's cloud top temperatures in infrared light. MODIS found cloud top temperatures of strongest thunderstorms were as cold as or colder than minus 80 degrees Fahrenheit (minus 62.2 Celsius) around the center. Cloud top temperatures that cold indicate strong storms that have the capability to create heavy rain.

National Hurricane Center (NHC) Forecaster Blake noted on Aug. 6 at 5 a.m. EDT that "The convective pattern of John has become significantly better organized during the past several hours, with a large central dense overcast forming and cloud top temperatures to minus 85 degrees Celsius."