The Winter Beach Erosion Outlook is based on a 42-year (1979-2020) hindcast of the Oceanic Nino Index (ONI) vs. local winter wave height anomalies, and a 18-year (2003-2020) hindcast of the wave anomalies vs. the observed winter beach width losses at Cardiff and Torrey Pines State Beaches.

Erosion is defined as the difference between the mean fall season and mean winter season beach width, or mean winter beach width loss. Probabilities are based on the probability of exceedance (POE, black line) of the historical mean winter beach width loss (grey solid line), and the +1 standard deviation winter beach width loss (grey dashed line) derived from Torrey Pines and Cardiff State Beach surveys since Jan, 2003.

An ensemble of the latest ONI forecasts for the upcoming Jan-Mar winter months, aggregated by the International Research Institute for Climate and Society at Columbia University, is used to seed the probabilistic model of beach width change.

This outlook is updated monthly from mid-September through mid-December following the mid-monthly update of the ONI forecast ensemble.