The National Oceanic and Atmospheric Administration (NOAA) has raised the odds that La Niña will develop this fall from last month to 70% and linger through the winter. It says while ENSO-neutral conditions were observed during September, the combined ocean and atmosphere system are more clearly trending toward La Niña conditions.
"All of the Niño regions cooled considerably during late September and early October, with the latest weekly value of Niño-3.4 index at -0.9°C," it states. "Subsurface temperature anomalies also decreased toward the end of the month, reflecting the strengthening of below-average temperatures at depth in the east-central equatorial Pacific. Atmospheric anomalies across the equatorial Pacific edged toward La Niña during September, with a stronger tendency toward La Niña late in the month."