https://phys.org/news/2018-07-aqua-satellite-super-typhoon-maria.html

At 11 a.m. EDT (1500 UTC) on July 6, 2018, the Joint Typhoon Warning Center (JTWC) noted that Super Typhoon Maria was packing maximum sustained winds near 155 mph (135 knots/250 kph). Maria was a strong Category 4 hurricane on the Saffir-Simpson Hurricane Wind Scale. Maria's eye was centered near 17.0 degrees north latitude and 141.2 degrees east longitude, about 480 nautical miles south of Iwo To island, Japan. Maria was moving to the northwest at 4.6 mph (4 knots/7.4 kph).

At that time, the JTWC noted that the "sharply-outlined 7-nautical mile wide eye that has constricted over the past 12 hours. This reduction in eye diameter plus the formation of a secondary outer eye wall, as observed in recent microwave images, indicate the cyclone is undergoing an eye wall replacement cycle."