Abstract Spring precipitation over western Central Asia (SCAP) experienced an abrupt and unprecedented wetting during 1988–2007, yet the relative contributions of external forcing and internal variability to this change and the underlying drivers remain unclear. Using observation data sets and large ensemble simulations, our study demonstrates that this wetting is dominated by internal climate variability. Specifically, mid‐high‐latitude North Atlantic sea‐surface temperature (NAS) variability drives interdecadal SCAP changes by exciting a Eurasian Rossby wave train, which enhances ascent motion over western Central Asia and promotes moisture transport into the region. A negative‐to‐positive NAS phase transition explains 44.82% of the 1988–2007 wetting, far exceeding the externally forced contribution (21.72%). Under mid‐intensity emission scenario, removing NAS‐related rainfall variability reduces near‐term SCAP projection uncertainty by 28.39%, highlighting NAS as a key source of predictability for hydroclimate risk on western Central Asia.