From Strong El Nino to Strong La Nina?
Over the past few months, we have had an El Nino. In fact, it has been one of the strongest El Ninos on record, and is one of the reasons why this past winter was generally quite warm, and why the Pacific Jet stream was so fast and active. It also helped to trigger the historic blizzard we had on January 22nd-23rd. Currently, while we still have an El Nino at the surface, conditions are rapidly flipping towards La Nina when one takes a deeper look at the oceans, as well as the trends in the climate models.
Under “normal” conditions, where there is no El Nino nor a La Nina, the trade winds are persistent in the Equatorial Pacific, which generally blow from east to west. This “pushes” the warmest Equatorial waters further west towards Australia and Indonesia, leaving cooler waters in their wake with more upwelling of subsurface cool water as well. Over the past year or so, these trade winds rapidly weakened and even reversed in some areas, allowing warm water to flow back eastward (instead of getting forced westward) towards the entire Equatorial Pacific, spreading eastward towards Peru. As warmer water builds, Oceanic Kelvin waves, which move from west to east — but also move up (upwelling) and down (downwelling) to transport warm or cool water vertically — are able to push warm water to strong depths and generate “pools” of warm water. This allows an El Nino to sustain itself, as even when a brief period of trade wind acceleration takes place and more upwelling happens, the water upwelled is still warm. It can take months to fully reserve a new El Nino equilibrium.
But finally, the proverbial rubber band is snapping.