EL NIÑO/SOUTHERN OSCILLATION (ENSO)

DIAGNOSTIC ADVISORY 96/1

issued by

CLIMATE PREDICTION CENTER/NCEP

January 16, 1996

Weak cold episode conditions continued in the tropical Pacific during December. Negative sea surface temperature (SST) anomalies continued throughout the equatorial Pacific east of the date line (Fig. 1), with anomalies more than 1.0°C below normal observed between 160°W and 140°W. Consistent with the SST anomaly pattern, convection during the last several months [as inferred from outgoing longwave radiation (OLR)] has been weaker than normal over the central and western equatorial Pacific, and enhanced throughout Indonesia and the eastern Indian Ocean (Fig. 2).

During December, the middle latitude upper-tropospheric circulation of the Southern Hemisphere featured anomalies consistent with cold episode conditions (weaker than normal westerlies at middle latitudes and stronger than normal westerlies at high latitudes, reflecting a poleward shift in the position of the middle latitude jet stream). Recent drier than normal conditions over central South America (southern Brazil, Uruguay and portions of Argentina), which is a feature of cold episodes, may be related to this pattern. The Northern Hemispheric circulation pattern during December, however, did not reflect typical cold episode conditions. Instead, the middle latitude westerlies over both the Pacific and Atlantic Oceans were stronger than normal associated with high latitude blocking in both regions.

Statistical predictions indicate a rapid decrease in the magnitude of the negative SST anomalies in the equatorial central Pacific during the next three to six months, with near-normal conditions returning to the region by mid-1996. The NCEP coupled model forecasts (Fig. 3) also show a rapid decrease in the magnitude of the negative SST anomalies, but with anomalies remaining slightly negative through mid-year. The two versions of the Lamont-Doherty Earth Observatory model indicate that central equatorial Pacific SSTs are likely to remain near or below normal through the end of 1996.

The ENSO advisories are available on the World Wide Web at http://nic.fb4.noaa.gov. Since our resources to produce and distribute the advisories are limited, we are forced to restrict the hard copy distribution. Therefore, we are requesting that users obtain the advisories electronically from the World Wide Web. However, if you require a hard copy version of the advisories, please contact the Climate Prediction Center using the e-mail address below.

Climate Prediction Center
National Centers for Environmental Prediction
NOAA/National Weather Service
World Weather Building
Washington, D.C. 20233
e-mail: wd52vk@hp31.wwb.noaa.gov


FIGURE 1. Anomalous sea surface temperature for December 1995. Contour interval is 0.5°C. Anomalies are departures from the adjusted OI climatology (Reynolds and Smith, J. Climate, 8, 1571-1583).


FIGURE 2. Time-longitude section of anomalous outgoing longwave radiation (OLR) (5°N - 5°S). Contour interval is 10 Wm-2. Anomalies less (greater) than -10 (10) Wm-2 and indicated by dark (light) shading. Anomalies are departures from the 1979-1988 pentad base period means. The data have been smoothed using a 5-pentad running mean filter.


FIGURE 3. Predicted 3-month average sea surface temperature anomalies from two recent versions of the NCEP coupled model (Ji et al. 1995, submitted to the J. Climate) for January - March 1996 (top), April - June 1996 (middle) and July - September 1996 (bottom). The forecasts are averages of three sets of forecasts initiated on approximately 15 October 1995, 15 November 1995, and 15 December 1995, respectively. Contour interval is 1°C, with additional contours for 0.5°C and -0.5°C. Negative anomalies are indicated by dashed contours.