Climate change-induced sea level rise (SLR) magnifies extreme sea level events, increasing the annual frequencies of high-tide floods (i.e., sunny-day floods) along the U.S. East Coast (USEC) in recent decades. Compounded by the effects of internal climate variability, the spatial and temporal evolution of coastal flooding exhibits large regional differences. By analyzing tide gauge observations, we find that the annual flooding time (FT; total days in a year when sea level exceeds the flooding threshold) has an accelerated increase from 2000-2020 compared to 1950-1970 along the USEC, particularly in the southern part of the Mid-Atlantic Bight (MAB) and northern part of the South Atlantic Bight (SAB) with the most rapid increase occurring in the past decade starting in ~2011.  By contrast, the flooding intensity has no apparent increase in most tide gauge locations. Interestingly, the acceleration of FT in the past decade along the southern MAB and northern SAB results primarily from the intraseasonal and decadal components of sea level anomalies (SLAs), with intraseasonal SLAs playing a more important role in southern MAB and a comparable role as decadal SLAs in SAB. Synoptic scale SLAs, which include the effect of storms, also have significant contributions in the MAB especially in the GOM. To understand the physical processes that cause the accelerated FT increase, we are carrying out model experiments using the ocean component of E3SM, to quantify the effects of surface wind stress versus buoyancy flux forcing. Statistical analyses are being performed to explore the linkages between the intraseasonal/decadal SLAs and climate variability modes.