Tropical Highlights -
the central and east-central equatorial Pacific, sea surface temperature
(SST) anomalies remained positive during December 2004.
The SST anomalies in the eastern equatorial Pacific have decreased
slightly, with a December value of 0.1 in the Niño 1+2 region (Fig. T18,
Table T2). The pattern of
tropical SSTs during December featured positive anomalies greater than +1.0°C
between 160°E and 120°W (Fig. T18).
The SST anomaly in the Niño 3.4 region increased to 0.9, the highest
value since January 2003 (Table T2).
Meanwhile, atmospheric features continued to show month-to-month
variability associated with intraseasonal (Madden-Julian Oscillation - MJO)
activity (Figs. T11, T12,
T13, Table T1).
- Darwin SOI (latest value -1.1,
Table T1, Fig. T1) has been negative during the past 7 months,
primarily in response to higher-than-average pressure over Darwin.
oceanic thermocline, measured by the depth of the 20°C
isotherm, remained deeper than average across most of the equatorial Pacific
during December (Figs. T15, T16). Consistent with these conditions,
oceanic temperatures at thermocline depth were 2-3°C
above average across most of the equatorial Pacific (Fig. T17).
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 January 2004 in
association with intraseasonal (Madden-Julian Oscillation) activity (Table
Near-average low-level winds were observed over
the equatorial Pacific during December 2004 (Fig. T20). The global
Tropics featured near-average convection, with the exception of enhanced
convection over the
(Fig. T25). Enhanced
convection was found across the subtropical
(Fig. T25, Fig. E3), associated with anomalous upper-level and
low-level troughs in that region (Fig. T20, T21) and enhanced
upper-level divergent flow (Figs. T23, T24).