We present a 12‐year (1981–93) near‐weekly oxygen‐isotope (δ18O) record from a western Australian (Ningaloo Reef) Porites lobata coral precisely positioned to record the sea‐surface temperature (SST) variation of the Leeuwin Current. The predictability of the Ningaloo Reef coral‐based SSTs may be unparalleled since it can be shown that SST changes in the Western Pacific Warm Pool (WPWP) are strongly correlated with, and lead by about 2.5 years, SST changes in the Leeuwin Current. Consequently, the ordinary SST variation in the Ningaloo coral record can be anticipated and removed to reveal unexpected cooling of 0.6°C (1992) and 0.9°C (1993) following the June 1991 eruption of Mt. Pinatubo. This cooling signal at Ningaloo Reef is likely to be produced by Pinatubo aerosol‐induced cooling of the southwestern WPWP averaging 0.5°C by early 1992 which is sustained at least through early 1993. It is suggested that this magnitude of volcanic cooling in the southwestern WPWP could have prolonged, in part, the extended 4‐year (1991–94) negative phase of the Southern Oscillation. Copyright 1995 by the American Geophysical Union.