Sea surface temperature (SST)
anomalies remained near-average across the western and central equatorial
Pacific during June 2004, and below average in the extreme eastern Pacific (Fig.
T18, Table T2), consistent with the neutral phase of the ENSO cycle.
Also, atmospheric indices continued to exhibit month-to-month
variability associated with intraseasonal (Madden-Julian Oscillations - MJO)
activity (Figs. T11, T12,
T13, Table T1).
The pattern of Tropical SST anomalies during June again featured
small positive values over the western and central Pacific and generally
small negative values over the eastern Pacific (Fig. T18).
The value in the Niņo 1+2 region decreased to -1.4, the lowest value
since June 2003, while the Niņo 4 value remained 0.5 (Table T2).
The oceanic 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,
although the magnitude of the anomalies decreased as the slope of the
thermocline decreased relative to May.
Consistent with these conditions, oceanic temperature anomalies at
thermocline depth decreased to 1-2°C
above average in the western and central equatorial Pacific and 2-3°C
below average in the eastern Pacific (Fig. T17).
The monthly 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 June, low-level westerly wind anomalies were observed over the
western equatorial Pacific and Indonesia, with actual westerly winds
observed north of the equator (Fig. T20).
Despite the intraseasonal activity, stronger-than-normal easterlies
have been dominant over the central Pacific since November 2003 (Fig. T13).
The global Tropics were
dominated by below-average convection during June, with the exception of
enhanced convection over the western Pacific (Fig. T25).
The enhanced convection extended north to 25°N, in a region that
experienced numerous tropical cyclones during the month.
MJO activity has contributed to increased variability over the
equator between 60°E and the date line since November 2003 (Fig. T11).
The Tahiti - Darwin SOI was -1.3 during June (Table
T1, Fig. T1), and the equatorial SOI decreased to -0.5 (Fig. T2).
The Tahiti - Darwin SOI has exhibited large month-to-month
variability since November 2003, in response to MJO activity (Fig. T10).
The equatorial SOI was negative for the first time since March 2003 (Fig.