El Niño/Southern Oscillation - November 2008
Neutral ENSO conditions remain, but in a cooler Pacific
Neutral ENSO conditions persisted for the sixth consecutive month, however sea surface temperatures (SSTs) remained below-average across much of the central and eastern equatorial Pacific Ocean.
All four Niño regions had slightly negative anomalies for October and November. The Niño 4 region SST anomaly was -0.26°C (-0.47°F), which is a decrease of -0.14°C (-0.25°F) compared with the October value of -0.12°C (-0.22°F). The Niño 3.4 region was the only region with an SST anomaly increase as its value rose from -0.26°C (-0.47°F) in October to -0.18°C (-0.32°F) in November; an increase of +0.08°C (+0.14°F). For the most recent equatorial Pacific Ocean surface temperatures, please visit NOAA's Tropical Atmosphere Ocean (TAO) project and for weekly or monthly Niño region average SST and anomaly values, visit CPC's Atmospheric and SST Index values page.
The subsurface oceanic heat content anomalies became increasingly negative as below-average temperatures at thermocline depth expanded throughout the central and eastern Pacific.
The 3-month (September-November) SST anomaly running mean in the Niño 3.4 region was -0.1°C (-0.18°F), which is well within the Oceanic Niño Index (ONI) threshold of -0.5°C (-0.9°F) for neutral conditions (NOTE: For NOAA's official ENSO classification scheme, please see NOAA's El Niño/La Niña Index Definition).
While a number of models suggest the development of La Niña during the next few months, the majority of the SST forecasts indicate ENSO-neutral conditions will continue into the first half of 2009. The CPC's December ENSO diagnostic discussion indicated that, based on current observations and recent trends, ENSO-neutral or La Niña conditions are equally likely through early 2009. The ENSO Wrap-Up from the Australian Bureau of Meteorology (BoM) also indicates the potential for a return to La Niña conditions.
Equatorial Zonal Winds (U-Component Winds) and Sea-Level Topography:
During November, low-level easterly winds and upper-level westerly winds expanded and strengthened across the equatorial Pacific Ocean. The recent strengthening of the low-level easterlies over the equatorial Pacific suggests the possibility of additional anomalous cooling of the SSTs. However, the magnitude of cooling remains uncertain and it is possible the La Niña threshold will not be met. Overall, the ocean-atmosphere system during November remained consistent with ENSO-neutral conditions, but exhibited several atmospheric characteristics typical of weak La Niña conditions.
Pacific sea levels measured by the NASA/JPL Jason-1 satellite reflected ENSO-neutral conditions across the tropical Pacific Ocean in November. Much of the central equatorial Pacific was near normal in November. However, cooler anomalies were more evident, spreading west of the Date Line during the month. An area of negative sea level anomalies persisted into November north and south of the Equator in the central Pacific, and substantial positive anomalies were present in the far western Pacific region.
OLR values increased slightly from +1.1 Wm-2 in October to +1.2 Wm-2 in November. The map below on the left shows the spatial pattern of global OLR (in Wm-2) measured by satellite during November. The lack of convection along the Equator near the Date Line has persisted since the development of the cold event in late May 2007.
The monthly OLR anomaly for November marked the 22nd consecutive month that the OLR index had a positive monthly value. Persistently high positive OLR indices are typical of the mature phase of a La Niña episode, while negative values indicate the presence of increased convection and warm phase conditions.
Convection remained enhanced over the western equatorial Pacific and suppressed near the International Date Line. However, in recent months intraseasonal variability has contributed to episodic strengthening and weakening of convection over the western equatorial Pacific.
Note that high frequency variability in OLR is typically associated with the Madden-Julian Oscillation (MJO), which is convective activity that propagates west to east in the near-equatorial region from the Indian Ocean into the Pacific Ocean approximately every 30-60 days. The latest MJO activity can be seen in CPC's graphs of Daily MJO Indices.
The Southern Oscillation Index (SOI) was once again positive in November. The standardized monthly averaged value rose to +1.5 from +1.3 in October. These SOI values generally correspond with ENSO-neutral conditions over the equatorial Pacific. [Consistently positive (negative) values of the SOI are typical of La Niña (El Niño) conditions.]
Addiontional El Niño/Southern Oscillation Links
- ENSO Monitoring
- NOAA El Niño Observations Page
- NOAA El Niño / La Niña Index Definition
- NOAA's Pacific Marine Environmental Laboratory (PMEL):
- NOAA's Climate Prediction Center (CPC):
- NOAA's Climate Diagnostics Center (CDC)
- NASA/JPL Ocean Surface Topography from Space
- Australian Bureau of Meteorology (BoM) ENSO Wrap-Up
- IRI - International Research Institute