Extending SST Anomaly Forecasts Through Simultaneous Decomposition of Seasonal and PDO Modes

TL;DR

This paper introduces a novel multivariate linear model that simultaneously decomposes seasonal and PDO modes to improve North Pacific SST forecasts, achieving unprecedented accuracy and extending forecast skill beyond 36 months.

Contribution

The study presents a new coupled decomposition approach that enhances SST forecast accuracy by integrating seasonal cycles and PDO dynamics within a multivariate linear framework.

Findings

Forecast skill extends beyond 36 months.

PDO projected to stay negative until late 2026.

Reduced likelihood of marine heatwaves in eastern North Pacific.

Abstract

We present a new approach to forecasting North Pacific Sea Surface Temperatures (SST) by recognizing that interannual variability primarily reflects amplitude changes in four dominant seasonal cycles. Our multivariate linear model simultaneously captures these amplitude-modulated seasonal cycles along with the Pacific Decadal Oscillation (PDO), which naturally emerges as an intrinsic feature of the system rather than a separate phenomenon. Using sixteen-dimensional regression based on four spatially distributed time series per variable, the model delivers unprecedented forecast accuracy for both interannual amplitude modulations and PDO evolution, maintaining skill beyond 36 months -- a substantial improvement over current operational and research forecasts, including machine learning methods. Predictions initialized in 2024 project that the PDO will remain in its negative phase through late 2026, implying reduced likelihood of severe marine heatwaves in the eastern North Pacific during this period. These findings have direct implications for regional climate impacts, including storm tracks, precipitation patterns, and marine ecosystem health. By treating seasonal and interannual variability as coupled rather than independent processes, this framework advances our understanding of North Pacific climate dynamics and provides a powerful tool for stakeholders managing climate-sensitive resources and planning adaptation strategies in regions strongly influenced by North Pacific conditions.