We need the trades colocated with the subsurface cold pool...we had that big time througout much of August, when we had the burst of intensification of La Nina due to the upwelling of the cold pool over the eastern half of ENSO. However, trades died down and shifted west in Septmeber. They look to pick up out east again next week and into October, but not as strongly as August. SOI has also been inching upwards. I think at the end of the day, the pedestrian coupling of the trades with the cold pool, owed at least in part to the diffuse PAC pressure dipole (Low west/high east) is what will have this La Nina struggling to be acknowledged by CPC in the record books. Will be very close.
The subsurface says game on...but the hemisphere isn't totally on board.