El Niño/Southern Oscillation (ENSO)

The tropical Pacific is in an ENSO–neutral state, havingcontinued to ease during June. Nevertheless, some weak remnants of the recent strong La Niña event remain. The NINO3 and NINO4 indices for June were +0.3°C and –0.4°C respectively (3-month means +0.2 and 0.4°C). Sub–surface temperature anomalies are positive across the Equatorial Pacific, apart from a shallow near-surface region near the Date Line (within NINO4), and upperocean heat content (top 300m) is also positive right across the Equatorial Pacific. The positive SST anomaly "horseshoe" in the extra-tropics is still evident, but the equatorial cold tongue has dissipated. In the  atmosphere, the SOI in June remain close to zero. The 3–month mean for AMJ 2001 was +1.0, as a consequence of the very high value in April. The TRMM ENSO index has weakened only slightly to a value of –0.8 for the 30 days to 26 June. Convection remains enhanced over the Philippines and parts of the Maritime Continent. The SPCZ is still displaced to the southwest of its normal position, but is somewhat disorganized as is typical of winter. Convection remains suppressed in a small region near the Date Line, south of the Equator. A weak MJO pulse moved into the western pacific in the second half of June.

The majority of the models NIWA monitor are predicting ENSO–neutral conditions over the July–September period. Three models indicate the development of weak El Niño conditions over late winter and spring, and two suggest redevelopment of a weak La Niña. The NCEP ENSO discussion of 9 June indicates an ENSO–neutral state through the winter season, with an uncertain status beyond that time. The IRI summary of 19 June expects neutral conditions for the remainder of 2011, but development of El Niño conditions or re-emergence of La Niña cannot be ruled out.