Tropical Highlights - October 2004

Sea surface temperature (SST) anomalies remained positive across the central and east-central equatorial Pacific during October 2004.   The SSTs in the eastern equatorial Pacific have increased from below average to near average, with an October value of 0.0 in the Niño 1+2 region (Fig. T18, Table T2).  The pattern of Tropical SSTs during October featured positive anomalies greater than +1.0°C between 160°E and 150°W (Fig. T18).  The SST anomaly in the Niño 3.4 region remained 0.8, the highest value since January 2003, and the Niño 4 anomaly remained 1.1, the highest value since November 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). 

The oceanic thermocline, measured by the depth of the 20°C isotherm, remained deeper than average in the western and central Pacific and deepened in the eastern Pacific during October (Figs. T15, T16). Consistent with these conditions, oceanic temperature anomalies at thermocline depth increased to 2-3°C above average in the eastern equatorial 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 (Madden-Julian Oscillation) activity (Table T1). 

During October, near-average low-level winds were observed over the central and eastern equatorial Pacific while low-level westerly anomalies (more than 3.0 m s^-1) were observed over the western equatorial Pacific (Fig. T20). The global Tropics featured near-average convection, with the exception of enhanced convection over the Indian Ocean (Fig. T25). The Tahiti - Darwin SOI was    -0.3 (Table T1, Fig. T1), and the equatorial SOI remained -0.2 (Fig. T2).  The Tahiti-Darwin SOI has been negative during the past 5 months, in response to higher-than-average pressure over Darwin .