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September 12, 2024
The NOAA National Centers for Environmental Prediction (NCEP) Climate Prediction
Center's (CPC) El Niño-Southern Oscillation (ENSO) Alert System is at
La Niña Watch.
ENSO-neutral continued during August 2024, with near-average sea surface
temperatures (SSTs) observed across most of the equatorial Pacific Ocean.
The weekly Niño indices did not change substantially during the month,
with the latest weekly index values varying between +0.2°C (Niño-4)
and -0.4°C (Niño-1+2). Below-average subsurface temperatures were
also similar to those in early August (area-averaged index). Negative
temperature anomalies continued to dominate across most of the subsurface
equatorial Pacific Ocean. Low-level wind anomalies were easterly over most of
the equatorial Pacific, and upper-level wind anomalies were easterly over the
east-central Pacific. Convection was slightly enhanced over parts of Indonesia
and was near average near the Date Line. Both the Southern Oscillation index
and the equatorial Southern Oscillation indices were positive. Collectively,
the coupled ocean-atmosphere system reflected ENSO-neutral.
The Columbia Climate School International Research Institute (IRI) for Climate and Society ENSO Predictions Plume predicts a weak and a short duration La Niña, as indicated by the Niño-3.4 index values less than -0.5°C, to emerge in the next couple of months and continue through the Northern Hemisphere winter. The continuation of negative subsurface temperatures and enhanced low-level easterly wind anomalies supports the formation of a weak La Niña. A weaker La Niña implies that it would be less likely to result in conventional winter impacts, though predictable signals could still influence the forecast guidance.
In summary, La Niña is favored to emerge in September-November (71% chance) and is expected to persist through January-March 2025.
... Read more
here
.
(The update of the CPC ENSO diagnostics discussion and forecast is scheduled
for the second Thursday of each month.)
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September 19, 2024
As of mid-September 2024, ENSO-neutral conditions persist in the western
equatorial Pacific, while oceanic and atmospheric indicators started to
show signs of La Niña development, including a sustained strengthening
of trade winds, and reduced convection over the central-eastern Pacific
during last two months. In line with the strengthened trades, the subsurface
cold temperature anomalies have also strengthened during recent weeks. The
IRI ENSO prediction plume forecasts equal chances for ENSO-neutral conditions
and La Niña for Sep-Nov, 2024. Borderline La Niña conditions are
forecasted during Oct-Dec (60% chances) that continue during the boreal winter.
ENSO-neutral conditions subsequently re-emerge as the most likely during the
boreal spring and remain so till the end of the forecast period.
According to the most recent official CPC ENSO Outlook (issued on September 12, 2024), the La Niña onset is forecasted in Sep-Nov, with 71% chances; however, the objective IRI model-based ENSO outlook forecasts indicate equal chances for La Niña and ENSO-neutral conditions for Sep-Nov 2024. Thus, there is a notable difference between the probability numbers in the early-month CPC Outlook and mid-month IRI ENSO forecast. The CPC ENSO Outlook predicts a clear preference for La Niña onset in Sep-Nov with continuation until Jan-Mar 2025 (63% chances), and then a return to ENSO-neutral state during boreal spring of 2025. In contrast, the objective IRI ENSO forecasts show a weak and short-lived La Niña conditions in Oct-Dec, 2024 through Jan-Mar, 2025. Both the CPC ENSO Outlook and the IRI ENSO forecast show a return to ENSO-neutral conditions boreal spring of 2025.
... Read more
here.
(The update of the IRI ENSO forecast is scheduled for the 19th of each month. If the 19th falls on a weekend or holiday, it is released on the closest business day.)
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, pictured directly above,
shows forecasts made by a set of dynamical and statistical models for SST in
the Niño-3.4 region, for nine, overlapping, three-month periods. The plume
indicates equal chances for La Niña and ENSO-neutral conditions during
Sep-Nov 2024. The multimodel mean of statistical models show ENSO-neutral
conditions during the entire forecasts period, however, the multimodel mean of
dynamical models show borderline La Niña conditions during boreal winter
of 2025, and then a return to ENSO-neutral conditions during boreal spring of 2025.
... Read more
here.
(The update of the IRI ENSO forecast is scheduled for the 19th of each month. If the 19th falls on a weekend or holiday, it is released on the closest business day.)
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