GNSS Ionosphere Mangkhut Interquartile Range Total electron content In this paper, we investigate the highest amplitude ionospheric variations, maximum sustained wind speed, and typhoon cloud during an extremely powerful tropical cyclone (TC) crossing through the South China Sea in September 2018 that caused extensive damage in Guam, the Philippines, and South China. Regional Ionosphere Maps (RIMs) were created through Hong Kong SatRef and IGS data around the Mangkhut Typhoon. RIMs are utilized to analyze the ionospheric response over the maximum wind speed points (maximum spots) after taking the solar-terrestrial environment and geomagnetic storm indices into consideration. The total electron content (TEC) time sequences over the maximum spots are detected by the method of interquartile range method (IQR) during super typhoon Mangkhut. The research findings indicating that significant ionospheric variations are detected over the maximum spots during the powerful typhoon within a few hours before the extreme wind speed. All the ionospheric variations are positive values. The infrared satellite snapshots confirmed that the maximum ionospheric perturbations do not coincide with the center of the storm but are detected in the area close to the typhoon edges. The possible ionospheric response mechanism is based on strong convective cells which create the gravity waves over TCs.