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 (CFS03) 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 using linear inverse modeling (Penland
and Magorian 1993: J. Climate, 6, 1067‑1076)
are shown in Figs. F9 and F10. Predictions from the ENSO‑CLIPER
statistical model (Knaff and Landsea 1997, Wea. Forecasting, 12, 633‑652)
are shown in Fig. F11. Niño 3.4
predictions are summarized in Fig. F12, 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 Advisory
Outlook:
La
Niña conditions are present and are likely to continue through the Northern
Hemisphere winter (~75% chance).
Discussion:
In
August, La Niña conditions were present, with below-average sea surface
temperatures (SSTs) extending across the central and eastern equatorial Pacific
Ocean (Fig. T18).
For the month, all Niño indices were negative, with the Niño-3.4 index
at -0.6ºC and the Niño-3 index was at -0.5ºC (Table T2). Equatorial subsurface temperature anomalies
averaged across 180°-100°W were negative, with the largest departures observed
in the east-central Pacific from the surface to 200m depth (Fig. T17). Atmospheric circulation anomalies over the
tropical Pacific were also generally consistent with La Niña, despite sub-seasonal
variability during the month. The
low-level and upper-level winds were near average for the month as a whole (Figs. T20
& T21), but enhanced low-level
easterly winds were prominent across the equatorial Pacific Ocean during early
and late August. Tropical convection
remained suppressed over the western and central Pacific, and was near average
over Indonesia (Fig. T25).
Both the Southern Oscillation and Equatorial Southern Oscillation
indices were positive (Table T1 & Fig. T2).
Overall, the coupled ocean-atmosphere system was consistent with La Niña
conditions.
A majority of the models in the IRI/CPC plume predict the
continuation of La Niña (Niño-3.4 index less than -0.5°C) through the Northern
Hemisphere winter 2020-21 (Figs. F1-F12). The forecaster consensus supports that view,
and favors a borderline moderate event (Niño-3.4 index near -1.0ºC) during the
peak November-January season. In
summary, La Niña conditions are present and are likely to continue through the
Northern Hemisphere winter (~75% chance).
Weekly
updates of oceanic and atmospheric conditions are available on the Climate
Prediction Center homepage (El
Niño/La Niña Current Conditions and Expert Discussions).