My guess is that there is not enough energy – geopotential or heat – in the western Pacific for another even moderate El Niño to emerge. A large El Niño needs time to recharge as warm surface water is piled up by Walker circulation in the western Pacific.
The 15/16 El Niño happened – followed by technically a La Niña Modoki and a small La Niña. What has it been doing in the last month?
It all starts with this – the trigger for nonlinear and powerful feedbacks in wind, cloud and current across the Pacific Ocean. The index of the polar annular mode – or Antarctic Oscillation reflects polar and sub-polar surface pressures. Cloudy and stormy winds circle the Antarctic with nothing impeding. Higher polar surface pressures pushes winds and storms into lower latitudes where they fetch up on the South American coast and feed into the South Pacific gyre. Cold southern water flows towards the equator where the currents whirl westward where it is added to with colder deep ocean upwelling kicking of La Niña and the ENSO recharge phase
The Antarctic Oscillation has been negative – more meridional blocking and south Pacific gyre flow – in recent weeks but is forecast positive at a crucial time in the seasonal evolution of the Pacific system.
It involves Walker and Hadley – iconic names in Earth system science – circulation. The earth,nullschool total precipitable water and windfields overlays show high moisture air moving across the north Pacific to the Gulf of Mexico, the Caribbean Sea and South America. I have highlighted a wet low. The south Pacific Ocean gyre kicks up a notch with negative AAO – blowing up the South American coast, diverging across the Pacific, south along the Australian coast – taking warm waters – to rejoin the circum-polar current and be spun up again by the southern polar annular mode (SAM).
Winds and the following cold, Southern Ocean currents are fetching up on the equator as we speak – driven there by a large high pressure blocking vortex west of South America. Is this enough to kick in La Niña feedbacks across the Pacific? Doesn’t look like it just yet.