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

MAY 2011

A transition from La Niña to ENSO-neutral conditions occurred during May 2011 as sea surface temperatures were near-average across much of the equatorial Pacific Ocean (Fig. T18, Table T2). The latest monthly Niño indices were -0.5°C for the Niño 3.4 region and +0.8°C for the Niño 1+2 region (Table T2, Fig. T5). Consistent with these conditions, the oceanic thermocline (measured by the depth of the 20°C isotherm) remained slightly deeper than average over the eastern equatorial Pacific (Figs. T15 and T16), with sub-surface temperatures reaching 1-3°C above average in this region (Fig. T17).

However, the atmospheric circulation patterns during May continued to show some weak La Niña impacts.  The equatorial low-level easterly trade winds and upper-level westerly winds remained stronger than average over the central equatorial Pacific (Table T1, Fig. T20), while convection remained enhanced over eastern Indonesia and suppressed across the central equatorial Pacific (Figs. T25 and E3). Collectively, these oceanic and atmospheric anomalies reflect a transition to ENSO-neutral conditions but with weakening La Niña impacts in the atmosphere.

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