sea surface temperatures (SSTs) during April 2007 were near-average across
the western and central equatorial Pacific and colder-than-average over the
eastern tropical Pacific (Fig. T18).
This pattern is reflected in negative values of the Niņo 1+2
(-1.1) and Niņo 3 (-0.3) SST indices, and by a near-zero (+0.1)
value of the Niņo 3.4 SST index (Table T2). Meanwhile,
Darwin SOI has
been slightly negative since February 2007, and was -0.4 in April (Table
T1, Figs. T1). These
conditions are consistent in indicating a continuation of ENSO-neutral
equatorial oceanic thermocline during April, measured by the depth of the 20ēC
isotherm, featured a continuation of below-average depths over the eastern
equatorial Pacific and near-average depths across the western and central
equatorial Pacific (Figs. T15,
T16). As a result, temperatures in the eastern
equatorial Pacific remained generally 2-5ēC below average at thermocline
depth (Fig. T17).
low-level easterly winds during April remained stronger than average over
the central equatorial Pacific (Fig. T20). This pattern has been very
persistent since February, and is consistent with the anomalously shallow
thermocline farther east. It is also consistent with the observed patterns
of anomalous tropical convection, with enhanced convection over the western
equatorial Pacific and suppressed convection across the central and eastern
equatorial Pacific (Figs. T25, E3).
In the subtropics and tropics, the 200-hPa atmospheric circulation anomalies
were consistent with this pattern of anomalous tropical convection, with
anticyclonic anomalies straddling the equator over the western Pacific, and
cyclonic anomalies straddling the equator in the vicinity of the date line (Fig.
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