Fig. 1-2: Daily Nino12 SSTA (left) and the 14-day change (right).
Discussion: During La Nina, the subsurface of the equatorial West Pacific is somewhat warmer than normal while in the equatorial East Pacific, the subsurface is cool. Trade winds up-well the cool waters east of the Dateline in the East Pacific forcing the cool SSTA pattern along the equator that sustains La Nina. Last December, a pulse of the convection phase of the Madden Julian oscillation emerged across the warm waters of the equatorial West Pacific and shifted eastward. In the equatorial East Pacific trade winds eased and La Nina intensity lowered. In the subsurface, the warming also shifted eastward as a Kelvin Wave. The NOAA animation (below) follows the eastward progress of the Kelvin Wave which arrived off the northwest coast of South America in late February. Consequently, a dramatic warming of surface waters in the Nino12 SSTA region has emerged. During the past 2 weeks waters have warmed by 1.55C in the Nino SSTA region according to CWG/Storm Vista WX Models. The only global SSTA models to predict this warming are ECMWF and METEO-France although the Nino12 warm-up is a little faster than each model predicted.
Watch animation of eastward-shifting equatorial Pacific subsurface Kelvin Wave.