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Use these links to access detailed analyses of Global and U.S. data. 
/ ANNUAL SUMMARY / ENSO LINKS /
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Warmer than average sea-surface temperatures (SST) persisted across the equatorial Pacific basin during December 2003. Ocean surface and sub-surface temperature anomalies in the central equatorial Pacific region were above average for the sixth consecutive month, as calculated using the reconstructed sea surface temperature data set developed by Dick Reynolds and Tom Smith at NCDC. The average SST anomaly during December in the Niño 3.4 region (when compared with the 1971-2000 base period) was +0.56° C (+1.01° F). The average temperature in the western equatorial Pacific, the Niño 4 region, was slightly cooler than the November average, but warmer than normal oceanic conditions occurred for the seventh consecutive month.
SST anomalies remained above average in the eastern Pacific region as well, but temperatures along the South American coast were not as anomalously warm as they had been in recent months. Temperature anomalies in the Niño 1+2 region became negative during the third week of the month but were above average near month's end. Ocean mixed-layer temperatures measured by NOAA's array of moored buoys remained warmer than average, particularly in the eastern Pacific. Sub-surface temperature anomalies exceeded +2° C east of 130° W. The warmer than average sub-surface conditions also continued to be reflected in the monthly average depth of the 20° C isotherm, which is used as an approximate depth of the thermocline that separates the mixed-layer from deeper water in the ocean. (The oceanic thermocline in the eastern Pacific is deeper during El Niño episodes.) During December, depth anomalies of the 20° C isotherm exceeded 50 m in the eastern equatorial Pacific region. The monthly averaged Southern Oscillation Index (SOI) abruptly shifted from negative to positive in December and was more strongly positive than at any time since early 2001 near the end of the last La Niña episode. The SOI was positive for only the second month in 2003 and for only the sixth time since early 2001. Satellite measurements of Outgoing Longwave Radiation (OLR) also remained anomalously positive in December, as they have since the dissipation of the last ENSO warm event in March, 2003. OLR anomalies have been consistently positive since April, 2003, which indicates that deep tropical convection has been suppressed in the central and western equatorial Pacific region. Therefore, no major changes in the atmospheric Walker Circulation have been observed in the Pacific basin despite the warmer than average SSTs observed across the region since July. KEYWORDS: ENSO; Niño Regions; Southern Oscillation Index (SOI); Kelvin Waves; Thermocline; Sea-Surface Temperatures (SSTs); Madden-Julian Oscillation (MJO); Walker Circulation |
December
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Sea-Surface Temperatures (SSTs) and
Mixed-Layer Conditions:
Sea surface temperatures in the central and eastern Equatorial Pacific were above average in
December, continuing a pattern of
warmer than normal conditions that began in
July.
For the latest oceanic temperature conditions, please see the loop of satellite images of December weekly SST anomalies.
In the oceanic mixed-layer, warm sub-surface anomalies that developed in the eastern equatorial Pacific in August remained in December. The warmest anomalies were centered near 110° W and were more than +2° C above average. In the western Pacific warm pool, a positive sub-surface temperature anomaly in the mixed-layer was again the dominant feature in the region this month, with the warm anomaly extending below 100 m depth over a broad region near the dateline (loop of December sub-surface ocean temperatures). The 20 °C isotherm remained deeper than normal across the eastern equatorial Pacific during December, with monthly averaged anomalies exceeding 25 m along and south of the equator from 100° W to 120° W. SSTs in the Niño 3.4 and Niño 4 regions were again warmer than normal based on data from NCDC's Extended Reconstructed Sea Surface Temperature dataset (ERSST) (map of Niño regions). This is the sixth and seventh consecutive months, respectively, where the observed SST anomalies were above average for the central and western Pacific Niño regions. The December anomaly in the Niño 3.4 region was +0.56° C (+1.01° F). A running three-month-mean SST anomaly above +0.5° C in the Niño 3.4 region is required for a warm event to be classified as an El Niño by NOAA. (For the official NOAA classification scheme, please see NOAA's El Niño/La Niña Index Definition and see the CPC ENSO Diagnostic Discussion for the latest official assessment of ENSO conditions.) |
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Equatorial Zonal Winds (U-Component Wind): There continued to be considerable variability in equatorial winds from week to week during December. Although the monthly averaged zonal (U-component) wind-field was near-normal in the equatorial Pacific in December, equatorial easterlies (negative U-Component winds) weakened in the western Pacific and westerlies developed near the dateline in late December. These conditions are reflected in positive zonal wind anomalies during the last week of the month in the central Pacific as shown in this animation of 5-day averaged zonal winds. These equatorial wind fields are measured by NOAA's Tropical Atmosphere-Ocean (TAO) Array buoy network. |
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Outgoing
Longwave Radiation (OLR):
There has also been considerable week-to-week variability in anomalies of Outgoing Longwave Radiation since the middle of 2003, and this continued in December. Tropical convection had been enhanced in the western equatorial Pacific during the Northern Hemisphere summer months (see the July and August monthly anomalies), but positive OLR anomalies were present in the western Pacific from mid-September through November. Negative OLR anomalies redeveloped in the western Pacific in late December, which is indicative of deep tropical convection and wetter-than-average conditions in that region. This is evident in the map to the left which shows average OLR anomalies from mid-December to mid-January. The week-to-week variability in OLR is associated with the Madden-Julian Oscillation (MJO). MJO related convective activity propagates west to east in the near-equatorial region from the Indian Ocean into the Pacific Ocean approximately every 30-60 days. From December through early January, MJO activity generated tropical convection that propagated east from the Indian Ocean to the western and central Pacific. The enhanced convective activity is represented by the blue colors on this image of 5-day running averages of the MJO index. The latest MJO event can be seen in CPC's graphs of Daily MJO Indices. |
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Southern Oscillation Index (SOI): The standardized SOI abruptly shifted from negative to positive in December. This was the first positive value for the index since July and only the second of the year, but it is not necessarily reflective of a shift toward the development of a La Nina episode. The slightly negative values of the past months have been indicative of near-neutral ENSO conditions. Continued monitoring of these and other conditions in the equatorial Pacific in coming months will help determine the evolution of ENSO. |
November
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Sea-Surface Temperatures (SSTs) and
Mixed-Layer Conditions:
Oceanic conditions in the equatorial Pacific remained above normal in
November. The warm anomalies in the SST pattern developed in
July and have continued into the fall
(Sep/Oct/Nov). For the latest oceanic temperature conditions, please see the loop of satellite images of November weekly SST anomalies.
In the oceanic mixed-layer, warm sub-surface anomalies that developed in August continued through November. In particular, a warm sub-surface anomaly that had developed in late August in the eastern Pacific, centered at approximately 120° W, remained anomalously warm during November. In the western Pacific warm pool, a positive sub-surface temperature anomaly in the mixed-layer was again the dominant feature in the region this month, with the warm anomaly extending below 100 m depth over a broad region near the dateline (loop of November sub-surface ocean temperatures). The 20 °C isotherm remained deeper than normal across the Equatorial Pacific during November, with monthly averaged anomalies exceeding 25 m along the equator in parts of the the eastern Pacific. SSTs in the Niño 3.4 and Niño 4 regions were again warmer than normal (map of Niño regions). This is the fifth and sixth consecutive months, respectively, where the observed SST anomalies were above average for the central and western Pacific Niño regions. The warm anomaly in the Niño 3.4 region was +0.54 °C (+0.97 °F) for the November mean. A running three-month-mean SST anomaly above +0.5 °C in the Niño 3.4 region is required for a warm event to be classified as an El Niño by NOAA (For the official NOAA classification, please see NOAA's El Niño/La Niña Index Definition). |
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Equatorial Zonal Winds (U-Component Wind):
The monthly averaged zonal (U-component) wind-field was near-normal in the equatorial Pacific in
November. Despite the near-average conditions for the month, positive zonal wind anomalies were observed during the middle and latter half of the month in the western and central Pacific. These positive U-component anomalies were associated with a weakening of the near-equatorial trade winds, as measured in NOAA's Tropical Atmosphere-Ocean (TAO) Array buoy network. In mid-November, the easterly trade winds (negative U-Component winds) decreased in velocity in the central Pacific, which also decreased equatorial upwelling. A loop of 5-day averaged zonal winds illustrates the observed relaxation of the near-equatorial trade winds in November. |
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Outgoing
Longwave Radiation (OLR):
Positive OLR monthly anomalies were measured in the western equatorial Pacific during November. These positive anomalies indicated that deep tropical convection was suppressed in the western Pacific region. Tropical convection had been enhanced in the western equatorial Pacific during the Northern Hemisphere summer months (see the July and August monthly anomalies), but positive OLR anomalies have been present in the western Pacific since mid-September, and these positive anomalies have increased since that time. Several high-frequency convective events have occurred during this period, but they have not been strong enough to offset the large-scale subsidence and suppression of convection averaged over monthly time-scales. Therefore, they are not typically resolved in the monthly OLR composite maps, such as in the a November 2003 OLR anomaly map. High frequency convective events are associated with the Madden-Julian Oscillation (MJO), and MJO related convective activity propagates west to east in the near-equatorial region from the Indian Ocean into the Pacific Ocean approximately every 30-60 days. During late October and early November, MJO activity generated tropical convection and westerly wind anomalies that were observed west of the dateline in the Pacific basin. The latest MJO event, along with a weaker event back in September, can be seen in CPC's graphs of Daily MJO Indices that are averaged at 5-day and 15-day intervals. In contrast to the positive OLR anomalies in the western equatorial Pacific, a negative OLR anomaly was present in the southwest Pacific. Specifically, a negative anomaly in the Coral Sea region northeast of Australia was observed in November, which indicated that convection was enhanced along the South Pacific Convergence Zone (SPCZ). No signficant negative OLR anomalies were observed during the month in the central and eastern equatorial Pacific, reflecting the lack of any organized tropical convection associated with anomalously warm SSTs east of the dateline. |
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Southern Oscillation Index (SOI): The standardized SOI remained slightly negative in November. This was the fourth consecutive month with a negative index value. Previously, the SOI shifted from a negative monthly mean in June to a positive monthly mean in July. Since the beginning of August, the SOI has been slightly negative, and has remained so through November. These slightly negative values for SOI are indicative of near-neutral ENSO conditions, and are consistent with the slightly warmer than average SSTs that have been present in the equatorial Pacific region since July. |
October
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Sea-Surface Temperatures (SSTs) and Mixed-Layer Conditions:
Oceanic conditions in the western and central equatorial Pacific remained above normal in
October. The warm anomalies in the SST pattern developed in
July and have continued through
Jul/Aug/Sep and into
Aug/Sep/Oct. The primary change in the oceanic conditions observed in October was the development of a warm SST anomaly in the eastern equatorial Pacific along the South American coast (see loop of satellite images of October weekly SST anomalies).
In the oceanic mixed-layer, warm sub-surface anomalies that developed in August continued through September and October. In particular, a warm sub-surface anomaly that had developed in late August in the eastern Pacific, centered at approximately120° W, remained anomalously warm during October. In the western Pacific warm pool, a positive sub-surface temperature anomaly in the mixed-layer was again the dominant feature of the region this month, with the warm anomaly extending below 100 m depth over a broad region west of the dateline (loop of sub-surface ocean temperatures in October). SSTs in the Niño 3.4 and Niño 4 regions were again warmer than normal (map of Niño regions). The warm anomaly in the Niño 3.4 region was +0.54 °C (+0.97 °F) for the October mean (NOTE: A running three-month-mean with an SST anomaly above +0.5 °C in the Niño 3.4 region is required for a warm event to be classified as an El Niño by NOAA. For the official NOAA classification see NOAA El Niño/La Niña Index Definition). The persistence of the observed positive SST anomalies since late-June has prompted NOAA's Climate Prediction Center (CPC) to predict the development of a borderline El Niño warm event by the end of November (see the latest CPC Press Release for details). |
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Equatorial Zonal Winds (U-Component Wind): The monthly averaged zonal (U-component) wind-field showed a slightly negative anomaly along the equator in October. This negative U-component anomaly was associated with a weakening of the near-equatorial trade winds, as measured in NOAA's Tropical Atmosphere-Ocean (TAO) Array buoy network. During the latter half of October, the easterly trade winds (negative U-Component winds) decreased substantially, with periods of westerly winds developing in the western and central equatorial Pacific. A loop of 5-day averaged October zonal winds illustrates the relaxation of the trade winds during the latter half of the month. A seasonal shift southward of the sub-tropical high pressure ridges is typical at this time of year, and likely contributed to this observed decrease in the trade winds in late-October. |
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Outgoing
Longwave Radiation (OLR):
Negative OLR monthly anomalies were measured in the western Pacific in the equatorial region during October. A negative anomaly developed just east of New Guinea, and another negative anomaly was measured just north of the equator along the dateline. These negative anomalies indicate that deep tropical convection was enhanced in the western Pacific region. It is likely that the enhanced convection was associated with an increase in Madden-Julian Oscillation (MJO) activity during the latter half of October in the western Pacific, since westerly wind anomalies were observed across the western half of the Pacific basin. In contrast to these negative OLR anomalies, a positive OLR anomaly was present in the southwest Pacific, specifically in the Coral Sea region northeast of Australia, which indicated that convection was suppressed along the South Pacific Convergence Zone (SPCZ). No signficant negative OLR anomalies were observed in October in the central and eastern equatorial Pacific, reflecting the lack of any organized tropical convection associated with anomalously warm SSTs east of the dateline. |
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Southern Oscillation Index (SOI): The standardized SOI remained slightly negative in October. This was the third consecutive month with a negative index value. Previously, the SOI shifted from a negative monthly mean in June to a positive monthly mean in July. Since the beginning of August the SOI has been slightly negative, and has remained so through October. These slightly negative values for SOI are indicative of near-neutral ENSO conditions, and are consistent with the slightly warmer than average SSTs that have been present in the equatorial Pacific region over the past several months. |
September
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Sea-Surface Temperatures (SSTs):
Oceanic conditions in the western and central equatorial Pacific remained slightly above normal in September. This SST pattern developed in July and continued during the Northern Hemisphere summer (July/August/September). In contrast to these warm SST anomalies, a cooler than average SST anomaly remained in the eastern equatorial Pacific and along the South American coast (see loop of satellite images of September weekly SST anomalies).
In the oceanic mixed-layer, two warm sub-surface anomalies that developed in August were again evident in September; a warm sub-surface anomaly in the western Pacific that extended below 100 m depth in a broad region west of the dateline, and a slightly warmer sub-surface anomaly below 50 m depth in the eastern Pacific centered at 120° W (loop of sub-surface ocean temperatures in September). SSTs in the Niño 3.4 and Niño 4 regions previously showed signs of developing cool anomalies and a trend towards La Niña conditions in June, but since that time the trend has reversed, with warm anomalies developing in both Niño regions (map of Niño regions). This warm anomaly in the Niño 3.4 region developed in July, increased slightly in August, but over the past month has decreased, with a +0.3 °C (+0.54 °F) anomaly for the September mean. |
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Equatorial Zonal Winds (U-Component Wind): The monthly averaged zonal (U-component) wind-field showed a slightly negative anomaly along the equator in September. This negative U-component anomaly was associated with a strengthening of the near-equatorial trade winds, as measured in NOAA's Tropical Atmosphere-Ocean (TAO) Array buoy network. However, shorter frequency fluctuations did occur during September, as the easterly trade winds decreased later in the month. A loop of 5-day averaged September zonal winds clearly shows a relaxation of the trade winds in the western and central Pacific region during the latter half of September. A seasonal shift southward of the sub-tropical high pressure ridges is typical at this time of year, and likely contributed to this observed decrease in the trade wind flow in late-September. |
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Outgoing
Longwave Radiation (OLR):
During September, a negative OLR monthly anomaly was measured in the western Pacific along the equatorial region. This negative anomaly developed immediately east of New Guinea, and indicated that deep tropical convection was enhanced in the far western Pacific. In contrast, a positive OLR anomaly was present in the southwest Pacific, in the region northeast of Australia, which indicated that convection was suppressed along the South Pacific Convergence Zone (SPCZ). No signficant OLR anomalies were present in September across the near-equatorial Pacific east of the dateline, reflecting near-neutral ENSO conditions. |
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Southern Oscillation Index (SOI): The Standardized SOI remained slightly negative in September. This was the second consecutive month with a negative index value. Previously, the SOI shifted from a negative monthly mean in June to a positive monthly mean in July. Despite these shifts, the SOI has remained near-zero since July, with slightly negative values the past two months. The near-zero values for SOI indicate that the atmospheric conditions associated with ENSO were near-neutral. |
August
WARM SST ANOMALY DEVELOPS IN THE NIÑO 3.4 REGION IN AUGUST
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Sea-Surface Temperatures (SSTs):
Oceanic conditions in the central equatorial Pacific Ocean warmed in August. The observed SST pattern developed in July and continued into August, as a warm SST anomaly developed across the western and central equatorial Pacific (see loop of satellite images of August weekly SST anomalies). In addition, this warming developed below the surface in the oceanic mixed-layer, where two warm sub-surface anomalies developed in August; a warm sub-surface anomaly in the western Pacific that extended below 100 m depth in a broad region west of the dateline, and another warm sub-surface anomaly below 50 m depth in the eastern Pacific centered at 110° W (loop of sub-surface ocean temperatures in August). SSTs during August measured by NOAA's Tropical Atmosphere-Ocean (TAO) Array of moored buoys were slightly above normal in the western and central equatorial Pacific, and a cool SST anomaly in the eastern equatorial Pacific remained confined to the waters off the South American coast. SSTs in the Niño 3.4 and Niño 4 regions previously showed signs of developing cool anomalies and a trend towards La Niña conditions in June, but since that time the trend reversed, with warm anomalies developing in both Niño regions in July and August (map of Niño regions). The warm anomaly increased in the Niño 3.4 region over the past month, with a 0.6 °C anomaly for the August mean. |
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Equatorial Zonal Winds (U-Component Wind): The monthly averaged zonal (u-component) wind-field was near-normal in August, but subtle variations were measured in NOAA's Tropical Atmosphere-Ocean (TAO) Array buoy network. For the month, a westerly surface wind anomaly occurred in the western equatorial Pacific, while there was an increase in easterly trade-winds in the eastern and central equatorial Pacific. A loop of 5-day averaged August zonal winds clearly shows a relaxation of the trade winds near the dateline during the first several weeks of August. |
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Outgoing
Longwave Radiation (OLR):
A positive OLR monthly anomaly was measured in the western equatorial Pacific in August. This positive OLR anomaly indicated that deep tropical convection was suppressed in the western Pacific, which likely contributed to the observed warming of the near-equatorial SSTs in this region. |
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Southern
Oscillation Index (SOI): The Standardized SOI switched signs in August, with a negative value for the month. Despite this shift in atmospheric pressure to a slightly negative SOI, the value remained near-zero, which indicates that the atmospheric conditions associated with ENSO are near-neutral for the month. |
July
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Sea-Surface Temperatures (SSTs):
SSTs across the equatorial Pacific Ocean remained near-normal in July. This trend toward near-neutral ENSO conditions began in early-June, and has continued into the Northern Hemisphere summer (see loop of satellite images of July weekly SST anomalies). SSTs during July measured by NOAA's Tropical Atmosphere-Ocean (TAO) Array of moored buoys were slightly above normal in the western and central equatorial Pacific, with a cool SST anomaly developing in the eastern equatorial Pacific and along the South American coast. SSTs in the Niño 3.4 and Niño 4 regions initially showed signs of developing cool anomalies and a trend towards La Niña conditions in May and early June, but since that time the trend has reversed, with weak warm anomalies developing in both Niño regions in July (map of Niño regions). |
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The trend from the cool SST anomalies toward neutral ENSO conditions in the central equatorial Pacific was associated with an eastward propagating oceanic Kelvin wave. This Kelvin wave was generated by enhanced westerly winds and relaxed trade winds in the western equatorial Pacific in late-May and early-June. It is likely that significant Madden-Julian Oscillation (MJO) activity during this time generated the anomalous westerly winds, and therefore the oceanic Kelvin wave. The overall effect of this Kelvin wave event was to inhibit the cool SST anomalies that were developing in late May and early June in the central and eastern equatorial Pacific. Westerly wind anomalies remained over the extreme western equatorial Pacific in July (For further information go to the NOAA CPC Current ENSO Diagnotics Discussion or the current IRI's Technical ENSO Discussion). |
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Outgoing
Longwave Radiation (OLR):
No significant OLR anomalies were present in the central and eastern equatorial Pacific in July, which is consistent with neutral ENSO conditions. An area of enhanced negative OLR anomalies persisted in the western equatorial Pacific region, north of Indonesia. Warm SSTs generated enhanced convection over this region in July, and therefore the negative OLR anomaly. |
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Southern Oscillation Index (SOI): The Standardized SOI switched signs in July, with a slightly positive value for the month. Despite this shift in atmospheric pressure to a slightly positive SOI, the value remained near-zero, which is consistent with near-neutral ENSO conditions. |
ENSO related Links
Questions?
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| Climate Services Division NOAA/National Climatic Data Center 151 Patton Avenue Asheville, NC 28801-5001 fax: 828-271-4876 phone: 828-271-4800 email: questions@ncdc.noaa.gov |
For comments and suggestions on this web page, contact:
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David Levinson NOAA/National Climatic Data Center 151 Patton Avenue Asheville, NC 28801-5001 fax: 828-271-4328 email: David.Levinson@noaa.gov |
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Jay Lawrimore NOAA/National Climatic Data Center 151 Patton Avenue Asheville, NC 28801-5001 fax: 828-271-4328 email: Jay.Lawrimore@noaa.gov |
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