Just a quick note for some of you guys bummed over the mild December. Many have noted that this la nina has continued to shifted eastward, at least as much, if not maybe a bit more so than I had expected.
Consider this excerpt from my write up last month regarding how the month of December can evolve differently based upon ENSO type.
There exist some notable differences between these two disparate types of la nina events. Here are a couple of schematics outlining these differences:
Differences between east-based La Nina's & central-based La Nina's
Figure A is east-based. Figure B is central-based
DJF 500mb for East-based years:
DJF Temps
Ironically in east-based years JFM is colder than Dec. Dec is typically the warmest month in the
east-based years, which runs counter to typical cold ENSO climo.
JFM 500mb east-based years
JFM Temps
Compare all of that to central-based La Nina years:
DJF 500mb
DJF Temps
December is the coldest month for central-based Nina's.
One thing worth noting is not all East-based Nina's are frigid, as there is variability due to the relatively weak
ocean-atmosphere coupling. This is because many east-based events, as is the case with modoki el nino events, are
weaker. You can have warmth, especially if the event is weaker, and one such case is 2005-2006.