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To better understand how individual processes combine to cause flooding and erosion events, we investigate the relative contribution of tides, waves, and nontidal residuals to extreme total water levels (TWLs) at the shoreline of U.S. West Coast sandy beaches. Extreme TWLs, defined as the observed annual maximum event and the simulated 100 year return level event, peak in Washington, and are on average larger in Washington and Oregon than in California. The relative contribution of wave‐induced and still water levels (SWL) to the 100 year TWL event is similar to that of the annual maximum event; however, the contribution of storm surge to the SWL doubles across events. Understanding the regional variability of TWLs will lead to a better understanding of how sea level rise, changes in storminess, and possible changes in the frequency of major El Niños may impact future coastal flooding and erosion along the U.S. West Coast and elsewhere. Regional differences in the magnitude and relative contribution of extreme TWLs exist along U.S. West Coast sandy beachesThe composition of extreme TWLs are dominated by wave runup, and the relative contribution of wave runup increases from north to southThe relative contribution of storm surge to the still water level doubles at most locations from the annual maximum TWL to the 100 year TWL

Hurricane Irma affected the Florida peninsula from 10 to 12 September 2017. The peninsula's east coast was hit hardest: the city of Jacksonville flooded around the St. Johns River estuary with storm surge that exceeded 1.5 m and rainfall that surpassed 20 cm in 24 hr. This study used observations such as water and wind velocities, river discharge, and salinity data to determine whether compounding forcings influenced flood levels. Results show that flooding was initiated by the ocean (first punch) and then exacerbated by river discharge (second punch). The 1–2 punch from the ocean and then the river caused record flooding, with impacts lasting through September. Peak storm surge occurred while winds were receding, and river discharge was increasing, rather than at the peak of either process. Compound flood models should consider the phase lag between driving processes, as the individual maxima may not occur simultaneously, yet still exacerbate flooding. Hurricane Irma affected the Florida peninsula in September 2017. The east coast of the peninsula was hit particularly hard: the city of Jacksonville flooded around the St. Johns River estuary with storm surge that exceeded 1.5 m and rainfall that surpassed 20 cm in 24 hr. This study used oceanic, atmospheric, and riverine observations to determine whether compounding forcings influenced flood levels. Results show that flooding was initiated by the ocean and then exacerbated by high river flows. The 1–2 punch from the ocean and then the river caused record flooding, with impacts that lasted through the rest of September. Peak storm surge occurred while hurricane winds were receding, and river flow was increasing. Storm‐related flooding models should consider the timing between ocean and river flooding, as the individual maxima may not occur simultaneously, yet still cause flooding. Compound flooding occurred during Hurricane Irma around Jacksonville, FloridaMaximum storm surge occurred extemporaneously to maximum winds and river dischargeCompound flooding occurred when the ocean obstructed the fluvial seaward discharge Compound flooding occurred during Hurricane Irma around Jacksonville, Florida Maximum storm surge occurred extemporaneously to maximum winds and river discharge Compound flooding occurred when the ocean obstructed the fluvial seaward discharge