Consistent with the pattern of SST anomalies, the equatorial oceanic thermocline remained shallower than normal across the eastern Pacific and deeper than normal in the western Pacific (Fig. T15). Also, subsurface oceanic temperatures remained more than 4°C above normal in the western Pacific, and more than 3°C below normal in the eastern Pacific (Fig. T17). During February, the thermocline shoaled between the date line and 125°W (Fig. T15), which resulted in a lessening of the temperature gradient across the central Pacific at thermocline depth.

Tropical convection during February remained below normal over the west-central and central Pacific [as inferred from positive anomalies of outgoing longwave radiation (OLR)] and well above normal over the extreme western Pacific, Indonesia, and northern Australia (Fig. T25). This pattern of anomalous convection is consistent with La Niña conditions and has largely persisted since mid-1998 (Fig. T8). Intraseasonal activity (Madden-Julian Oscillation-MJO) intensified during February (Fig. T11), as a strong MJO enhanced convection over the Indian Ocean and Indonsesia.

The anomalous tropical convection during February was associated with low-level (850 hPa) easterly wind anomalies over the western equatorial Pacific and westerly wind anomalies over the eastern Indian Ocean (Figs. T7, T20, and Table T1). Enhanced equatorial easterlies have persisted across the western and central Pacific since the onset of cold episode conditions in mid-1998 (Fig. T7). At upper levels, large westerly wind anomalies (15 - 20 ms^-1) over the central equatorial Pacific were associated with strong cyclonic circulation anomalies flanking the region of suppressed convection (Fig. T21, T22). This resulted in a 200-hPa zonal wind index value of 3.0, equaling the largest value observed (February 1989) in the historical record dating back to 1979 (Fig. T3). This pattern of upper-level and lower level wind anomalies is consistent with an increased strength of the equatorial Walker circulation (Fig. T29).