An unusual heat in October
It’s not often you mention the words humidex and October in the same sentence. But that was the case for some communities hitting the low 20s in Atlantic Canada this week, breaking temperature records.
Despite an early frost in parts of the region, October has been warmer than usual.
So why has it been so warm?
Two main factors contribute to the late-season warmth here in Atlantic Canada.
The first has been a blocking ridge of high-pressure, which has dominated our weather pattern for the second half of the month.
While this ridge has shifted somewhat with the passage of other weather systems, it has been the dominant feature in the upper levels for the last couple of weeks, pulling in warmer air to our south and systems with tropical moisture.
Another critical factor is the above-normal sea surface temperatures in the Atlantic Ocean, something that’s become a new normal.
Both Earl and Fiona were powerful enough to bring colder water to the surface, allowing for a period of below-normal sea surface temperatures.
However, any sign of that has vanished, with seasurface temperatures currently running on average about two to five degrees above normal just offshore.
This is significant as the ocean is a major influencer on the climate in Atlantic Canada. Often with ocean temperatures running above normal, we will also experience above normal-air temperatures.
The unusual warmth does moderate heading into this weekend, but with periods of near or above seasonal temperatures to end the month, we will need to see if any monthly records fall.
It’s another sign of our changing climate.