Climate scientists typically monitor Niño Region 3.4 as to the presence of an El Niño.
Right now, Niño 3.4 is considered “inactive” with a reading of +0.5°C.
However, take a look at sea surface temperature departures (SST) further out in the central Pacific -- within Niño Region 4.0. Sea surface temperature departures within this region are significantly warmer -- +1.0°.
There is an alternate, and rarer, type of El Niño that you might not be familiar with called a Modoki El Niño.
Modoki is Japanese for “same but different.” Modoki events are a rarer subset of regular El Niño’s and are marked by warmer water centered in the central Pacific.
Here are SST anomalies associated with a Modoki El Niño. Note that the core of strongest warming is located within the center of the Pacific.
This plot shows that Central Pacific SST departures (Niño 4.0) are currently warmer than Eastern Pacific (Niño 3.4).
And NMME long-range climate model forecasts above-normal SST’s to persist across the Central Pacific through the winter months.
Assuming little change in current SST departures, it’s possible that winter precipitation impacts could align with a Modoki El Niño (right-below).
A linkage between warm tropical water and the sub-tropical jet stream, via convection, could steer moisture across Mexico and towards the South Central U.S.
This would result in an unusually-dry California and an increase in winter precipitation over the southeast and the eastern U.S.
This year’s Blob of unusually-warm North Pacific SST is the second-largest marine heatwave recorded in the Pacific in at least the last 40 years, covering 4 million square miles.
The abnormally warm waters extend from Alaska to Canada and as far west as Hawaii. That includes a large swath of water that’s more than 3 degrees Celsius (5.4 degrees Fahrenheit) hotter than normal for this time of year.
This unusually-warm water can have a persistent impact on the position of the jet stream. In the past, the jet stream has been pushed further north than normal over the western U.S. before dipping south over the Midwest. In other words, a “wavier” jet stream.
It’s possible that the jet stream will bow unusually-far north around this area of warm water. This would result in a dip in the jet stream and resulting intrusions of cold arctic air into the middle and eastern U.S.
This wavy jet stream could also reduce California and West Coast precipitation.
The unusually-warm Pacific Ocean is likely to influence the position of the jet stream this winter and shape temperature and precipitation anomalies.
However, keep in mind that there is no assurance that these warm pools will persist. Also, in addition to warm Pacific water, there are numerous other factors that will influence winter weather.