Transitional MJO Weakens Strong -GLAAM; Highly Amplified Mid-latitude Pattern to Ease
10/13/2025, 7:11 am EDT
The Warm Oceans, Causal to Warm Medium-range Forecasts
10/15/2025, 7:01 am EDT
Climate Impact Company Weekly ENSO Climate Diagnostics
Issued: Tuesday October 14, 2025
Highlight: Nino SSTA are neutral despite onset of La Nina announcement by NOAA.
Discussion: Last week, the Nino SSTA regions each warmed slightly and are all in neutral range as mid-October approaches (Fig. 1). Despite neutral Nino SSTA, NOAA announced La Nina onset last Thursday. The subsurface equatorial East Pacific is broadly cooler than normal (Fig. 2). The trend is slightly cooler from 2 weeks ago. The cool subsurface is fuel for La Nina once trade winds return to near or above normal velocity. The Madden Julian oscillation (MJO) shift across the tropical Indian Ocean the next 1-2 weeks should force positive southern oscillation index (SOI) which inspires trade winds to up-well cool waters of the East pacific subsurface and cause Nino SSTA to cool later this month.
Fig. 1: The 12-week monitor of the Nino SSTA regions indicates the Nino34 SSTA is at the La Nina threshold.
Fig. 2: The equatorial Pacific Ocean upper ocean heat anomalies.