temperature (SST) anomalies continued to increase across the central and
east-central equatorial Pacific during August 2004, and remained negative in
the eastern equatorial Pacific (Fig. T18, Table
T2). Meanwhile, the
atmospheric indices continued to show month-to-month variability associated
with intraseasonal (Madden-Julian Oscillation - MJO) activity (Figs. T11,
T12, T13, Table
T1). The pattern
of Tropical SSTs during August featured positive anomalies greater than +1.0°C
between 175°E and 130°W and negative anomalies less than -1.0°C east of
100°W (Fig. T18).
The SST anomaly in the Niño 3.4 region increased to 0.8, the highest
value since January 2003, and the Niño 4 anomaly increased to 0.9, the
highest value since November 2003 (Table T2).
In contrast, the anomaly in the Niño 1+2 region remained negative (Table
thermocline, measured by the depth of the 20°C
isotherm, remained deeper than average in the western and central Pacific
and shallower than average in the eastern Pacific (Figs. T15,
with these conditions, oceanic temperature anomalies at thermocline depth
increased to 3-4°C
above average in the western and central equatorial Pacific and remained 2-3°C
below average in the eastern Pacific (Fig. T17).
low-level (850-hPa) and upper-level (200-hPa) equatorial zonal wind indices,
the Tahiti-Darwin SOI and the outgoing longwave radiation (OLR) index have
all exhibited considerable variability since November 2003 in association
with intraseasonal activity (Table T1).
During August, near-normal low-level winds were observed over the
central and eastern equatorial Pacific (Fig. T20),
in contrast to the large low-level westerly wind anomalies over the central
equatorial Pacific observed during July.
global Tropics featured near-normal convection for the second month in a row
Across the tropical Pacific, negative OLR anomalies near 15°N
indicate a northward shift of the ITCZ.
MJO activity has contributed to increased variability over the
equator between 60°E and the date line since November 2003 (Fig.
- Darwin SOI was -0.8 during August (Table T1, Fig.
T1), and the equatorial SOI decreased to -0.2 (Fig.
T2). The Tahiti - Darwin
SOI has exhibited large month-to-month variability since November 2003, in
response to MJO activity (Fig. T10),
although it has been negative during the past 3 months, in response to
higher than normal pressure over Darwin.