This study examines the statistical characteristics of the eyewall evolution induced by the landfall process and terrain interaction over Luzon Island of the Philippines and Taiwan. Interesting eyewall evolution processes include the eyewall expansion during landfall, followed by contraction in some cases after re-emergence in warm ocean waters. Best track data, advanced satellite microwave imagers, high spatial and temporal ground-observed radar images and rain gauges are utilized to study this unique eyewall evolution process. An examination of the available microwave images of 23 typhoons crossing the Philippines between 2000 and 2010 shows that most typhoons experienced this kind of eyewall evolution, i.e., the radius of the eyewall for 87% of landfall typhoons increased during landfall; and, the radius of the eyewall for 57% of the cases contracted when the typhoons reentered the ocean after they crossed the Philippines. Furthermore, analyses of large-scale environmental conditions show that small vertical wind shear, high low-level relative humidity and sea surface temperature are important for the reorganization of the outer eyewall and the subsequent eyewall contraction when the typhoons reentered the ocean.
For typhoons that crossed Taiwan, based on the microwave and radar images, 89% of the cases show an expansion of the eyewall during landfall. However, the reorganization of the outer eyewall and subsequent contraction were rarely observed due to the small fraction of the ocean when the typhoons entered the Taiwan Strait. In addition, observed rainfall shows an expansion in the rainfall area induced by terrain.