Sea surface temperature (SST)
anomalies remained above average across the equatorial
during August 2009 (Fig. T18).
of the Niņo-region SST indices were between +0.8°C and +1.0°C throughout the
The oceanic thermocline along
the equator, measured by the depth of the 20°C
isotherm, remained deeper than average across the equatorial
during August (Figs. T15, T16).
Consistent with these conditions, temperatures were 1o-3oC
above average at thermocline depth across the equatorial Pacific (Fig. T17).
during August, convection was suppressed across
and the western Pacific (Figs.
T25, E3). The coupling of the
oceanic and atmospheric anomalies indicates a weak El Niņo.
tropical circulation also featured intra-seasonal activity associated with the
MJO (Fig. T12),
which masked the El Niņo-related pattern of enhanced convection over the
central equatorial Pacific. The MJO also produced a westerly wind burst in the
western tropical Pacific early in the month (Fig.
T13), which triggered an eastward propagating
oceanic Kelvin wave. This wave contributed to a deepening of the oceanic
thermocline during the month, and to in increase in oceanic heat content in the
central equatorial Pacific (Fig. T17).
Previously, the upwelling phase of a Kelvin wave had led to a temporary
weakening of the positive sub-surface temperature anomalies in the eastern
convection was enhanced over the eastern tropical Pacific during August, in
association with a very active month of tropical cyclone activities in that
region. Over the tropical
, the ITCZ was shifted
north of normal, in association with an enhanced west African monsoon
circulation (Fig. T24),
weaker than average easterly trade winds in the deep tropics (Fig.
T20), and a northward shift of the 700-hPa
African easterly jet. These conditions contributed to the development of four
named storms (including
Major Hurricane Bill), despite anomalous upper-level westerly winds (Fig. T21) and increased vertical wind
shear over the
in association with El Niņo.
the latest status of the ENSO cycle see the ENSO Diagnostic Discussion at: