Tropical Highlights

  Table of Atmospheric Indices  (Table 1)

  Table of Oceanic Indices  (Table 2)

  Time Series

  Time-Longitude Sections

  Mean & Anomaly Fields

  Appendix 1: Outside Contributions

Tropical Highlights

DECEMBER 2007

A moderate-strength La Niña continued during December 2007. This is reflected by a continuation since October of below-average equatorial sea surface temperatures (SSTs) from west of the Date Line to the South American coast (Figs. T9, T18). The equatorial SSTs were more than 1.5°C below average east of 170^oW during December (Figs. T9, T18), which is consistent with the negative values of the latest monthly Niño-3.4 index (-1.5°C) and the monthly Niño-1+2 index (-2.0°C) (Table T2). The sub-surface temperature departures remained negative across the eastern equatorial Pacific, where temperatures at thermocline depth ranged from -2°C to -4°C below average (Fig. T17).

During December 2007, strong low-level easterly anomalies (more than 3.0 m s^-1) spanned the western and central equatorial Pacific – in fact, the 850 mb wind index in the western Pacific (+3.7) is the largest value observed in the historical record back to 1979 (Fig. T20, Table T1). This pattern is consistent with a continued shallower-than-average thermocline in the central and eastern equatorial Pacific (Figs. T15, T16). These conditions were associated with enhanced convection (above-average rainfall amounts) across the eastern tropical Indian Ocean and Indonesia and a continuation of suppressed convection (below-average rainfall amounts) across the central and eastern equatorial Pacific (Figs. T25, T26, E3). Consistent with these anomalies, the Tahiti – Darwin SOI was +1.8 during December (Table T1, Fig. T1).

For the latest status of the ENSO cycle see the ENSO Diagnostic Discussion at: 
            http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html