Abstract Coastal internal tides are considered unpredictable: harmonic fits to depth‐varying baroclinic velocity explain little variance. We show the depth‐averaged coastal internal tide is predictable from astronomical forcing. On the inner shelf, coastal trapped wave (CTW) modes are approximately depth‐uniform, so depth‐averaging recovers their coherent sum at the forcing frequency, while multimodal interference degrades coherence in depth‐varying velocity. SUNTANS simulations of M2 ${M}{2}$‐forced CTWs in the Southern California Bight produce coherent phase propagation over several hundred km, sustained by distributed generation along the coast. Applying a harmonic skill score to seven‐year ADCP records at three inner‐shelf sites yields a 35 percentage point SS90 ${mathrm{S}mathrm{S} }{90}$ gap between depth‐varying and depth‐averaged projections. Tidal‐band motions are ∼28% of alongshore variance, ∼73% of it depth‐averaged and dominated by the trapped wave, not surface tides. Predictability requires a slope supporting CTW generation at the relevant frequency and an analysis variable capturing the depth‐averaged response.