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

APRIL 2009

A transition from La Niña to ENSO -neutral conditions was observed during April 2009, as negative sea surface temperature (SST) anomalies further weakened across the equatorial Pacific Ocean and positive anomalies developed in areas of the eastern Pacific (Fig. T18).  The latest monthly SST index was -0.2°C in the Niño-3.4 region, and 0.0°C in the Niño-4 region (Table T2, Fig. T5).

The oceanic thermocline along the equator, measured by the depth of the 20°C isotherm, remained deeper than average across the Pacific and shallower than average in the far eastern Pacific during April (Figs. T15, T16). Consistent with these conditions, temperatures were 1-3^oC above average at thermocline depth across the equatorial Pacific (Fig. T17). Convection remained suppressed over the central equatorial Pacific Ocean and enhanced in the western Pacific (Figs. T25 and E3). Collectively, this combination of oceanic and atmospheric conditions reflects a transition from weak La Niña to ENSO -neutral conditions.

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