**5. Summary and conclusions**

An objective method is developed to categorize concentric eyewall structures in the western North Pacific (WNP) TCs using the NRL SSM/I and TMI satellite imagery database. For the WNP (ATL) basin, there are 91 (33) CE TCs and 113 (50) CE cases identified from 29,785 (19,001) satellite images between 1997 and 2014. Excluding the cases that are 200 km close to landfall and cases with temporal resolution higher than12 h, 83 (34) CE cases were studied for the structural and intensity changes. The primary findings are as follows:


region. After CE formation, however, the unfavorable environment that is created by ENSO may reduce the TC intensity quickly.
