Forecast Forum
The canonical correlation analysis (CCA) forecast of
SST in the central Pacific (Barnett et al. 1988, Science, 241,
192‑196; Barnston and Ropelewski
1992, J. Climate, 5, 1316‑1345), is shown in Figs. F1
and F2. This forecast is produced routinely by the Prediction Branch of the
Climate Prediction Center. The predictions from the
National Centers for Environmental Prediction (NCEP) Coupled Forecast System
Model (CFSv2) are presented in Figs. F3 and F4a, F4b. Predictions
from the Markov model (Xue, et al. 2000: J.
Climate, 13, 849‑871) are shown in Figs. F5 and F6. Predictions
from the latest version of the LDEO model (Chen et al. 2000: Geophys. Res. Let., 27, 2585‑2587)
are shown in Figs. F7 and F8. Predictions from the ENSO‑CLIPER
statistical model (Knaff and Landsea
1997, Wea. Forecasting, 12, 633‑652)
are shown in Fig. F9. Niño 3.4
predictions are summarized in Fig. F10, provided by the Forecasting and
Prediction Research Group of the IRI.
The CPC and the contributors to the Forecast Forum caution
potential users of this predictive information that they can expect only modest
skill.
ENSO Alert System Status: La Niña Watch
Outlook:
A transition from
ENSO-neutral to La Niña is favored in the next couple of months, with a 70-80%
chance of La Niña during the Northern Hemisphere winter 2021-22.
Discussion:
In
the last month, ENSO-neutral continued with near-to-below average sea surface
temperatures (SSTs) persisting in the central and eastern equatorial Pacific (Fig. T18).
Aside from Niño-1+2, the rest of the monthly Niño index values ranged from -0.2C
to -0.4C (Table T2). Negative subsurface temperature
anomalies (averaged from 180-100ºW) remained steady in August, reflecting
below-average temperatures that extended from the surface to ~250m depth in the
eastern Pacific Ocean (Fig. T17). Low-level wind anomalies were
easterly over the western Pacific Ocean, while upper-level wind anomalies were
westerly over the western and east-central Pacific (Fig. T20 & T21). Tropical convection was suppressed
near and west of the Date Line and enhanced over Indonesia (Fig. T25).
Given these conditions, the ocean-atmosphere system reflected ENSO-neutral, but
is edging toward La Niña.
The
IRI/CPC plume average of forecasts for the Niño-3.4 SST region from the last
month favored borderline or weak La Niña during the fall and winter 2021-22 (Figs. F1-F12). The forecaster consensus
this month, however, favors the latest predictions from the NCEP CFSv2 and the
North American Multi-Model Ensemble, which suggest higher chances for the
emergence of La Niña. At this time,
forecasters anticipate La Niña to be of weak strength (seasonal average Niño-3.4
index values between -0.5C to -0.9C). In summary, a transition from ENSO-neutral to La Niña is favored in the next couple of
months, with a 70-80% chance of La Niña during the Northern Hemisphere winter
2021-22.
Weekly
updates of oceanic and atmospheric conditions are available on the Climate
Prediction Center homepage (El
Niño/La Niña Current Conditions and Expert Discussions).