I called it on Monday, noting meteorological discussion of the specific characteristics of the storm, which was:
Sea surface temperatures underneath the area of activity are below the usual threshold of 26C, however, upper level temperatures are cold enough that the storm could develop some tropical characteristics.
It’s not becoming subtropical because of global warming; it’s becoming subtropical because, while the ocean surface temperature is below the usual threshold for storm formation, the upper level temperatures are so cold that the storm could [did] take on some tropical characteristics.
According to The Weather Channel’s Tropical update web page, a subtropical storm
has a few characteristics of both an extratropical low and a tropical cyclone. First, it has convection, or thunderstorm activity, around a well-defined center of circulation. Second, it has become detached from its associated fronts (cold, warm, occluded). Finally, it has sustained gale/tropical storm force winds.
Unlike a tropical cyclone, this is a cold-core system and its strongest winds are found miles away from the center of circulation; not tightly wrapped around the center.
The Associated Press story on Andrea concludes with the following:
[T]he Intergovernmental Panel on Climate Change, a U.N.-sponsored group, says global warming caused by humans has led to an increase in stronger hurricanes.
Have they forgotten? Global warming is now supposed to be responsible for less intense hurricanes, not more intense ones:
Global warming could increase a climate phenomenon known as wind shear that inhibits Atlantic hurricanes, a potentially positive result of climate change, according to new research released on Tuesday. … Wind shear, a difference in wind speed or direction at different altitudes, tends to tear apart tropical cyclones, preventing nascent ones from growing and already-formed hurricanes from becoming the monster storms that cause the most damage.
