What is a ‘sting jet’? Understanding the storm that exploded off Newfoundland.
An offshore storm exploded in intensity as it slammed Newfoundland on Tuesday with hurricane-force winds. Though the system was not a tropical one, it contained damaging gusts over 75 mph and offshore winds exceeding 120 mph, rivaling a Category 2 hurricane – thanks to something called a “sting jet.”
The worst of the storm stayed offshore, yet a 96-mph gust was reported on Sagona Island in the Gulf of St. Lawrence – which didn’t even get hit by the sting jet.So what produced this intense extratropical cyclone?
- – -
Conditions that formed the storm
On Monday morning, a weak wave of low pressure was present off North Carolina’s Outer Banks. That surface low became energized as a potent upper-air disturbance worked overhead. Air was efficiently lifted up and away from the surface low, leaving less air in the middle. Within 24 hours, the system’s air pressure dropped by more than 7 percent – meaning about 7 percent of the air is essentially missing from the middle of the storm.
The rate of intensification was twice what was required to classify it as a bomb cyclone – an ominous meteorological term for a midlatitude storm with a certain threshold of dropping air pressure. For this kind of storm with even greater intensity, some meteorologists have crafted informal terms like “double bomb.”
That missing air at the storm’s middle created an inward vacuum effect of sorts, driving strong winds.
Some of the winds stem from the low-level jet stream, or a river of warm air about a mile above the ground rushing into the storm out of the south. That brought 60- to 70-mph winds to the coastal Avalon Peninsula on Tuesday afternoon. St. John’s saw a 68-mph gust at 11 p.m. Tuesday and a 66-mph gust early Wednesday. An inch or two of rain was also expected.
To the west, Saint-Pierre Airport gusted to 78 mph as the core of the low pressure came ashore Tuesday evening.
The most remarkable part of the storm, however, was the anticipated development of a sting jet.
- – -What is a sting jet?
It is a small but intense “stinger” of 100 to 120 mph winds. Sting jets occur on the back side of intense low-pressure systems. They are most common over the open ocean but can occasionally brush ashore or clip the Canadian Maritimes, affecting land.
Sting jets form in the comma head, or wraparound, of low-pressure weather systems. Strong winds aloft blow clouds into the low-pressure system’s “dry slot,” which is the wedge of dry air swept along into the circulation.
The moisture in the clouds evaporates, drying the air. Dry air is dense, so it sinks. In the process, that sinking air drags strong winds to the ground. That means the strongest winds may actually accompany clear skies.
Meteorologists are still unsure what other processes are at play and what exactly jump-starts the development of a sting jet. It is estimated that between 39% and 49% of the strongest low-pressure systems produce sting jets. They are most likely to form following a bout of “bombogenesis,” or rapid strengthening, when a low-pressure cyclone is mature.
Sting jets have happened in the United States a couple of times, but no place is as prone to them as Western Europe – particularly northern Spain, Ireland and Scotland. Sometimes, the winds barrel into England and Wales, too.
Atmospheric scientists did not even know sting jets existed until the Great Storm of 1987, when a run-of-the-mill October storm unleashed 120-mph winds. Shoreham-by-Sea in Sussex, England, logged a 120-mph gust, while Pointe du Roc in Granville, in the Normandy region of France, gusted to 137 mph. The culprit was a sting jet.
Satellite imagery confirms a sting jet did occur. While it fortunately stayed south of Newfoundland over the harsh North Atlantic, it would have brought hurricane conditions if any mariners were present in the area.
- – -
Did the storm have an eye?
Sort of, but not really. On Tuesday afternoon, the storm system’s center cleared out, leaving a dearth of cloud cover in the middle. It looked like an eye on satellite.
But, technically speaking, nor’easters and mid-latitude storm systems don’t have eyes in the way that hurricanes have eyes. That’s because the internal processes of the storms are entirely different.
A strong hurricane can develop a clear eye when rising air in the eyewall collides with the “ceiling” of the lower atmosphere; some of the air bounces back down, subsiding, sinking, heating up and drying out. That punches out a hollow, clear eye at the storm’s center. Hurricanes are warm-core systems; the eye may be 10 to 20 degrees warmer than the surrounding air.
Mid-latitude cyclones form from, and feed off of, completely different processes. They’re “cold-core” systems too. They simply can’t harbor the same processes that generate an eye in a hurricane.
So what caused the eye-like feature? It was just a “seclusion,” or a pinched-off pocket of dry air from the “dry slot,” as the storm wrapped back on itself. It doesn’t have any significance other than looking cool – and marking where the center of low pressure is.