Synopsis: La Niña will likely continue into early 2008.
La Niña continued to strengthen during October 2007, as equatorial sea surface temperature (SST) anomalies became increasingly negative from 170oE to the South American coast (Fig. 1). The latest 4-week analysis shows the largest SST departures (-2ºC to -3ºC) located between 140oW and the South American coast, with departures of -0.5oC to -1oC observed near the Date Line (Fig. 2). All of the Niño region indices, except for Niño-4, remained lower than -1.0oC (Fig. 3) indicating that La Niña is approaching moderate-strength (3-month running mean value of the Niño 3.4 index below -1.0oC).
Also during October, the upper-ocean heat content (average temperatures in the upper 300 m of the ocean) in the central and east-central equatorial Pacific remained below average (Fig. 4), with temperatures ranging from 2oC to 6oC below average at thermocline depth (Fig. 5). Consistent with these oceanic conditions, the low-level easterly winds and upper-level westerly winds remained stronger than average across the central equatorial Pacific, convection remained suppressed throughout the central and eastern equatorial Pacific, and an area of slightly enhanced convection covered parts of the far western Pacific. Collectively, these oceanic and atmospheric conditions reflect La Niña.
The recent SST forecasts (dynamical and statistical models) for the Niño 3.4 region indicate a continuation of La Niña into early 2008 (Fig. 6). Over half of the models indicate at least a moderate La Niña through December, followed by gradual weakening thereafter. Current atmospheric and oceanic conditions and recent trends are consistent with the model forecasts.
Expected La Niña impacts during November – January include a continuation of above-average precipitation over Indonesia and below-average precipitation over the central equatorial Pacific. For the contiguous United States, potential impacts include above average precipitation in the Northern Rockies, Northern California, and in southern and eastern regions of the Pacific Northwest. Below-average precipitation is expected across the southern tier, particularly in the southwestern and southeastern states.
This discussion is a consolidated effort of NOAA and its
funded institutions. Oceanic and atmospheric conditions are updated weekly on the Climate Prediction Center web
site (El Niño/La Niña Current
Conditions and Expert Discussions). Forecasts for the evolution of El Niño/La Niña are updated monthly in the
Forecast Forum section of CPC's Climate
Diagnostics Bulletin. The next ENSO Diagnostics Discussion is scheduled for 6 December 2007. To receive
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