Summary of current conditions in the Tropical Pacific

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Dr. McPhaden summarized current environmental conditions in the equatorial Pacific as observed from the real-time TAO data stream. The period July 1994 to March 1995 was characterized by warm SST anomalies (>1°C) near the date line, with largest amplitudes (over 2°C) during October December 1994. Warm SST anomalies were also evident in the eastern Pacific, though smaller in amplitude and somewhat more restricted in time (October 1994 February 1995). Anomalies progressively weakened throughout 1995, such that by September 1995 (concurrent with TIP-4) cold anomalies of 0.5° - 1.0°C appeared all along the equator east of the date line (Figure 1). These conditions contrasted dramatically with those from late 1994 when 1°- 2° warm anomalies were found in the same region. Associated with the equatorial cooling, the trade winds were 1 - 2 m s stronger than normal, again in sharp contrast to the 3 - 4 m s weaker than normal trades late last year. Along the equator, the thermocline (as measured by the depth of the 20°C isotherm) was shallower than normal by 10 - 20 m between 160°W and 120°W, and near normal elsewhere in September 1995. There was evidence in the central and eastern Pacific in September 1995 of upwelling Kelvin wave propagation forced by a strengthening of the easterlies west of the date line in August. According to NOAA's Climate Diagnostics Bulletin (Climate Prediction Center, 1995) the Southern Oscillation Index (SOI) increased from values near -1 in late 1994 to slightly positive by September 1995. During the same period, deep convection migrated from near the date line to 120° - 140°E. These trends indicate a termination of the 1994 - 95 ENSO event, and the possible development of a cold event (La Nina). Several climate prediction schemes (model based and statistical) published in the September 1995 Climate Diagnostics Bulletin indicate a continuation of cold conditions in the equatorial Pacific at least through late boreal winter 1996.

Reference

Climate Prediction Center, 1995: Climate Diagnostics Bulletin, September 1995. U.S. Dept. of Commerce, Washington, DC, 77pp.

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