as mentioned, this is a well documented consequence of climate change. climate science saw this coming decades ago, although it wasn't supposed to happen for years.
further, there is no "battle" between the polar vortex and the warm oceans this time of year. that happens in the spring. at this time of year, the el nino event actually mildly amplified the weakening vortex.
the weakening vortex means less cold air, not more cold air.
further, the temperatures are warm (at least where i am) due to warm water in the atlantic creating a high pressure system, and not due to el nino.
regarding the forecast, there is little reason to think the vortex is going to restrengthen at this time of year given that we're getting close to the solstice, which is when it starts breaking up. there is still not a large enough temperature difference for the vortex to strengthen.
the vortex may actually reverse a second time and a third time, without strengthening and without creating a concentration of cold air to spill out. that's what we would expect to see on a planet undergoing a runaway greenhouse effect.