Tuesday, September 8, 2015

Global SST Anomalies Exhibiting Significant Changes

There are a number of changes underway across the globe with respect to sea surface temperature anomalies, a number of which may impact our coming winter, should these changes persist into the cold season.

The above animation shows sea surface temperatures across the globe over the last several weeks on the top panel, with anomalies for the same time period on the bottom panel. We're going to focus our attention today on the bottom animation, and I will refer frequently back to that bottom panel. There are four important items we need to analyze in this post.

1. Warming Waters Southwest of California
Over the last few weeks, an arm of increasingly-warming waters has been protruding from the Baja California region towards the central Equatorial Pacific. As of the last update on this animation, there is a small sliver of 3ยบ C above normal water anomalies in this swath. Over the last two winters, we saw a warm pool in the Gulf of Alaska provide a semi-permanent ridge, delivering those intense Arctic air outbreaks. A positioning of warm waters to the south could have a similar effect, but if it maintains into the winter, my gut tells me we could see something of a suppressed ridge along the Southwest coastline, which could be bad news for those in California hoping for a wet winter.

2. Sudden Warming in the North Atlantic
This event has only commenced in the last couple of weeks, and it remains to be seen how long it can persist. It appears the previously-cool waters in the north Atlantic are now experiencing rapid warming, stemming from well above normal waters off the East Coast of the United States. This development proves intriguing, as the cold waters stationed near Greenland would have encouraged a positive NAO pattern to develop in the winter, which would be favorable for warm, calm weather in the East US. However, if this warming can sustain and flourish in the north Atlantic, the situation could turn more interesting, particularly for winter weather fans in the East US.

3. Warm Waters in the Indian Ocean
There has been some gradual warming of surface temperatures in the Indian Ocean over the past few weeks. You might be asking, what does that have to do with the United States? Well, those warmer waters could very well encourage increased tropical convection in that area. That region is where the Madden-Julian Oscillation phases 2-5 tend to be, come winter-time. If you didn't get what that means, it can be summed up like this: increased storms in the Indian Ocean could prove favorable for those wishing for a warm winter in the eastern 2/3rds of the country.

4. Gulf of Alaska Warmth Migrating West
This may be the most pivotal development in this post, narrowly beating out the Central Pacific warming. The infamous Gulf of Alaska warm pool, which has been stagnant over the past two winters, allowing frequent and brutal intrusions of Arctic air, appears to be making a move to the west. Over the past few weeks we have seen the strongest positive SST anomalies make a shift from the Gulf of Alaska to the waters due south of the western Aleutian Islands. If this warm pool stops in that part of the Pacific, the risk of a warm winter in the Central US spikes. If it keeps pushing west, then we have a whole new ballgame. It could also migrate back east into the Gulf of Alaska. The point is, there's a lot of uncertainty, which isn't good, since this could be a critical part of the coming winter.

To summarize:
- There are a number of global sea surface temperature anomalies undergoing changes in recent weeks.
- These changes are proving to be favorable for both another harsh winter, but also a warm winter.
- We remain a few months away from winter, so there is a lot of time for these factors to change yet again.