https://phys.org/news/2018-10-nasa-powerful-hurricane-sergio-temperature.html

AIRS temperature data showed Sergio had intensified that morning, with the eye becoming better defined while embedded in very cold cloud tops. AIRS detected those very cold cloud tops were as cold as or colder than 207 Kelvin (minus 87 degrees Fahrenheit/minus 66.1 degrees Celsius). Storms with cloud top temperatures that cold have the capability to produce heavy rainfall.

At 5 a.m. EDT (0900 UTC) on Thursday, Oct. 4 the National Hurricane Center or NHC noted "Sergio's intensity is estimated to have increased just a little more this morning, and it remains a powerful category 4 hurricane."