ENSO ADVISORY NO.1

525 PM EDT Mon. Nov. 24, 2011

SYNOPSIS

Below normal sea surface temperatures associated with La Nina conditions strengthened across the east-central equatorial Pacific Ocean in October. The recent weekly sea surface temperature index values in the Nino-3.4 and Nino-3 regions dropped to near -1.0C. Also, the oceanic heat content temperature in the upper 300m of the ocean remained below normal values. The atmospheric circulation over the tropics featured strong week-to-week variability during October in response to the Madden Julian Oscillation. Averaged over the month, convection remained suppressed near the Date Line in association with La Nina, but was near normal over Indonesia as the Madden Julian Oscillation acted to offset the increased convection typically associated with La Nina. Also, anomalous low-level easterly and upper-level westerly winds shifted into the western Pacific and over Papua New Guinea.

FORECAST

A majority of the models now predict La Niña to continue through the Northern Hemisphere winter and then gradually weaken after peaking during the November - January period. Over the last half-century, La Nina events that were preceded by ENSO-neutral conditions during the Northern Hemisphere summer (May-August) were less likely to attain strong amplitude the following winter. This observation, in combination with the model forecasts, favors a weak to moderate strength La Nina during the Northern Hemisphere winter.

Jim G. Munley, jr.
http://www.jimmunleywx.com