Subtropical Storm Adria has to form today or its window of opportunity will close
The non-tropical low-pressure system we’ve been following across the North Atlantic all week is likely down to its last day to get named. Either it quickly sheds its fronts – a legacy of its days as a coastal low off the Carolinas last weekend – or it gets absorbed by another big North Atlantic system that's hot on its heels before it can get named.
To be designated a subtropical storm, a system has to become independent of the fronts that were attached to it when it formed in the first place. Unlike purely tropical system, northern low-pressure systems form from the contrast of cold and warm air. The boundaries between those air masses are the fronts. Over the ocean, if a system sits over warmish water long enough, the circulation can sometimes become an independent entity. That’s what the National Hurricane Center is looking for.
Unlike Wanda last week, this system has not stalled over warm enough water, and it has also not found a calm pocket of upper-level winds. So it’s retained a mostly non-tropical structure.
Now, a second, strengthening non-tropical low-pressure system is bearing down on it, which is forecast to begin to absorb potential-Adria beginning later today or tomorrow. Thus it’s now or never if Adria is going to form. In any case, it would only be around for a hot minute.
The name would jump right to Subtropical Storm Adria because the system already has winds over 40 mph. Yesterday, satellites measured hurricane force winds in the circulation. If it had been named, it still would have been called Subtropical Storm Adria, however. There is no classification of subtropical hurricane. If subtropical systems have hurricane-force winds, they normally either weaken quickly or evolve into regular tropical hurricanes.
The National Hurricane Center is only giving this system a slight chance of getting named today. And those chances will become very low by tonight.
Elsewhere, the Atlantic is in a wintertime posture. While we can never rule out one of these non-tropical systems sitting over warm-enough water long enough to evolve into a named system, it wouldn’t affect us. Let’s assume hurricane season is over until or unless proven otherwise.