Wednesday, January 13, 2016

The Tropics Attacking the Arctic

There is a subtropical storm in the Atlantic Ocean. While the formation of a northern-hemisphere subtropical storm in January is odd enough, the forecast track is odd in its own right. Tropical systems can’t meaningfully be predicted a week in advance, but the National Hurricane Center forecast track (below) suggests that the storm is likely to pass east of Greenland. If that comes to pass, there is a fair chance of the storm reaching the Arctic Circle with wind, waves, and relatively warm air — “the tropics attacking the sea ice,” as one observer put it. It is rare enough that such an event happens in summer. For it to appear in the forecast in January, the coldest month in the Northern Hemisphere, suggests that the balance of power has shifted.

The Arctic could never win a fight with the tropics anyway, for the simple fact that the tropics are ten times as large. The Arctic can hold on well only by avoiding any direct confrontation with the tropics. But if a tropical-influenced event — Subtropical Storm Alex formed just outside the tropics with the aid of tropical air — can reach out and poke the Arctic in January, then where is the place for the Arctic to hide?

It used to be that the jet stream would protect the Arctic from tropical incursions, but this week, the jet stream is too busy pouring cold air into mid-continent regions to help out over the open ocean.

The Arctic has already seen a major ice-melting event this month, and the remnants of Alex could be a second. It is early enough in winter for the ice to recover effectively, but only if there aren’t two more similar storms over the next two months. In other words, the health of the Arctic sea ice is tenuous enough that it depends on random chance. Random chance being what it is, it is just a matter of time before the tropics and the Arctic have a fight that the Arctic can’t run away from.

Update, January 14: Alex reached hurricane status and has the unmistakable signature of a hurricane on the satellite picture. The forecast suggests it could remain a hurricane for a day, giving it a stronger chance of holding together into the Arctic. The forecast track has not changed much.