After windstorm Barra which hit western Europe through early December, North Atlantic is now developing another powerful extratropical low – a bomb cyclone. It will be the worst storm of the winter season 2022/22 for the region. On Thursday, strong hurricane-force winds will be felt in the region. Also, major waves are expected to reach Iceland and western Europe.
The North Atlantic has become a more dynamic weather system recently thanks to the Polar Vortex’s southern lobe that has brought a strong winterstorm across North America and into the Ocean this week. An extratropical storm developed overnight, pushing its central tension below 960mbar by Wednesday morning.
Tonight’s forecast predicts a lower low.
Although the region has not seen any extratropical storms of this intensity this winter, it will see this storm. The wind intensity, central pressure, and size.
Below, you can see the structure of the geocolor satellite image of Wednesday morning. It shows the typical structure of a huge dry conveyor belt wrapping around the core and organization of a rapidly developing system to the east. Also notice the large intrusions of cold air that it leaves behind, a classic illustration of a rapidly evolving cyclone.
The central pressure has already dropped to 25 mbar since the system entered the Northwest Atlantic. This pressure drop has intensified over the past 24hours. Through Thursday morning, the storm is expected to intensify (more than 30mbar in 24hrs).
This rapid intensification of central pressure is called the bombogenesis process. It also refers to a bomb cyclone, which is a sudden and extreme drop in pressure. To be classified as a bomb cyclone, a system must experience a pressure change of more 24 mbar within 24 hours.
This powerful storm in the North Atlantic will produce hurricane-force winds. The highest gusts are likely to peak above 200 km/h due a textbook forecast of a stingjet wind maximum forecast. Below is satellite animation indicating storm development since Tuesday evening.
This bomb cyclone is expected to produce a wide channel wind of powerful winds and major waves. The large swell and most of the North Atlantic will reach Iceland and the western European coasts on Thursday and Friday.
A BOMB CYCLONE DEVELOPMENT – HOW SUCH STORM FORMS?
This pressure change we are seeing with this low also indicates that the system has been classified as a bomb-cyclone. In other words, the system is intensifying while its central pressure falls very rapidly. Bomb cyclones form when explosive cyclogenesis or bombogenesis occurs, which is characterized by a rapid deepening and acceleration of its barometric tension.
A system must have a minimum pressure change of 24 millibars within 24hrs to be classified as a bomb-cyclone. A bomb cyclone can also be called an extratropical or non-tropical cyclone. It is a cyclone that develops very quickly from a low pressure system. An example of the bomb cyclone is seen above, this is Nor’Easter along the U.S. coast.
The extratropical hurricane can grow very large and often dominates a large part of the ocean. This is the case in our case for the North Atlantic (or North Pacific on other occasions). These types of cyclones tend to move towards the northeast. Because of its large size, it generates hurricane-force winds that can cause severe to very severe damage and massive waves.
A bomb cyclone, just like an extratropical storm, is fueled by variations in temperature. This is precisely what happens between warmer temperatures towards Equator, and cooler temperatures towards Arctic. The temperature also changes vertically throughout atmosphere. This Atlantic cyclone differs from the tropical cyclones which we normally see during hurricane season. These cyclones get their energy from the extremely warm sea surface temperatures found within the tropical region.
These types of cyclones thrive on the east coasts in the late autumn/fall or winter months. The combination of Arctic cold continental air mass with warm, moist oceantropical air mass gives a lot of energy for cyclones to quickly develop or explode over the Atlantic.
Bomb cyclones are very common in the North Atlantic winter months, but they can also occur throughout the year. They also include posttropical systems, which can rapidly form from a decaying tropical storm when they travel north towards Europe.
Each year, Earth is home to between 60-70 bomb cyclones. The Northern Hemisphere is home to about two-thirds (50), with the majority of them located off the east coasts, especially the U.S., and the North Atlantic. The rest are located in the northwestern Pacific, around Japan. Australia can experience multiple bomb cyclones every year, but they rarely have the same intensity as the Pacific or North Atlantic storms.
BOMB CYCLONE PRESSURE DROPS IN 24 HOURS AT 45 mbar
WV satellite imagery on Wednesday already shows a striking structure of the storm. The system is developing with a large core and surrounded by a wide cold maritime air mass. The storm’s aftermath has seen a lot Arctic cold mass moving from eastern Canada into Northwest Atlantic.
As the low continues to move northeast across North Atlantic, it is going through its bombogenesis process. It is expected that it will become an extratropical storm by Thursday morning. Its structure will be spectacular at peak intensity, with the typical appearance cloud bands symmetrically wrapped around a tightening core.
Wednesday morning saw the central pressure of cyclone rise to 974mbar. This is accompanied by a rapid fall rate. Below is the NOAA Ocean Prediction Center’s (OPC) surface analysis data. It shows the average sea-level pressure estimates. The extratropical thunderstorm was located eastwards of Newfoundland in Northwest Atlantic. It then moved northeast.
The forecast arrows show that the central pressure of this extratropical storm will drop by 43 mbar in the next 24 hours, between Wednesday 00 UTC (UTC) and Thursday 00 UTC (UTC). This is almost twice what is required for explosive cyclogenesis, and the pressure change is quite remarkable.
The new North Atlantic extratropical hurricane will be a very powerful system. The bombogenesis process is expected to be complete by Thursday morning. Also resulting in a remarkable pressure difference between the Azores High and the Icelandic Low tonight – more than 100 mbar!
You can see how tightly pressure gradients (isobars), are spread between these large-scale systems. This will make the jet stream intense. This will allow winds to be stronger towards the surface.
This is actually a very common pattern in the winter months of the North Atlantic. It happens after intense Arctic outbreaks from Greenland, Canada, and Greenland reach the warmer North Atlantic. Explosive cyclogenesis is often the outcome.
BOMB CYLCONE DOMINATES MOST OF THE NORTH ATLANTIC.
The bomb cyclone will continue to grow across the North Atlantic through Wednesday night. The central pressure should continue falling rapidly and will reach its lowest point at 930 mbar by Thursday morning. Near-surface winds will increase.
The tight pressure gradient will remain through Thursday. It will support large areas of severe hurricane winds, creating major waves/swells towards the east or northeast. Peak wind gusts are expected to reach hurricane-force speeds at around 200 km/h near central low.
These particularly intense winds are caused by the sting jet wind maximum, which is the main driver.
WHAT IS A STING JET?
The sting jet phenomenon is a source of extremely intense winds. It can produce wind gusts exceeding 150 km/h and sometimes as high as 200 km/h. It is a narrow, strong zone of winds that originates in the mid-tropospheric storm head of explosive or bomb cyclogenesis.
As the jet descends towards its surface, winds are intensified further because it is drying out and evaporating clear paths through the precipitation. The jet’s evaporative cooling causes the air to become denser and accelerates the flow towards the cloud head tip.
Peak wind gusts associated with the sting jet are often in excess of 90 mph (150 km/h)m fairly easily recognizable as the cloud, hooked like a scorpion’s tail. This gives the violent wind region its name the ‘sting jet’. It typically affects a smaller area than the parent bomb cyclone and lasts for only a few hours. It can cause severe winds to the land.
Here is how it looks like:
A typical extratropical storm is composed of two frontal zones, the warm front and cold front. A strong flow cold air, also known as a cold conveyor belt, develops in the cyclone ahead the warm front. The dry intrusion is usually formed by the cooler, drier air mass that flows behind the main cold front.
The cold conveyor belt transports cold, moist air towards central cyclone. It also brings precipitation in the form of rain and snow. The dry intrusion is cool, but very dry, air that enters the cyclone. With the precipitation falling onto the cold conveyor belt, it evaporates into the dry interusion and cools the air further through evaporative cooler.
These processes take place at altitudes between 3-4km. Because the cooled air is denser than surrounding air, it descends quickly towards the surface. This creates even stronger winds within an already intense wind field from the cyclone.
This narrow region of cooled, accelerated aer is what is known as the sting jet.
With the typical satellite appearance of the banded cloud heads, strongly curved into the cyclone we can see this scorpion’s tail and stinger alike shape. These cloud bands are caused by the evaporation of dry intrusion air and can be quite abrupt.
HURRICANE-FORCE WINDS AND MASSIVE WAVES/SWELL SPREAD TOWARDS ICELAND AND IRELAND
Although the sting jet wind’s maximum effects will remain far from the European land and will be limited to the areas around the center of the bomb cyclone, severe winds will still spread across a broad area over the Atlantic Ocean.
The system will turn north-northeast Wednesday night and the majority of the winds will reach southern Greenland, and southwestern Iceland. This will mature the system and stop the rapid intensification.
Some of these winds could also be felt towards the Faroe Islands, Ireland and Scotland as well as southwestern England and the Bay of Biscay. Locally, the peak gusts will average between 90-110 km/h. The most affected areas of land will be in south and southwest Iceland. The pea gusts will reach 120 km/h at their highest, with higher levels in areas where the downslope flow is enhanced by the slopy terrain.
Tonight’s tight pressure gradient will produce major waves that reach close to 15 meters south of the low by Thursday morning. These waves will affect southwestern Iceland in a gradual manner, and they will spread across a large area.
As the extratropical hurricane matures on Thursday, it moves westward along southeast Iceland. This will push the major waves further east towards western Europe by Friday. The waves will reach the coasts of western Ireland at 10-12 meters in height and the swell will be strong.
On Friday, major waves will reach the Bay of Biscay despite the wind decreasing but spreading over a wider area than during the rapid intensification of the bomb cyclone tonight.
A large swell will be associated this large North Atlantic system. Expect significant waves along these western coastlines from Portugal to Scotland starting Friday into the weekend.
Southern Iceland will also have a significant snowpack until Saturday, due to the Southerly general circulation over the North Atlantic. However, most of the snow will accumulate on the higher ground.
Also, notice the impressive snow band that runs along the moving Bomb Cyclone from the southeast tip to Newfoundland towards southeast Greenland. The cyclones will gradually degrade on Friday. These areas will receive 100-200cm of fresh snow within a matter of days.
There is also the possibility of fresh snow in the northern UK, particularly in the Scottish Highlands.
Images used in this article were provided courtesy of Windy and Wxcharts.
Canada’s Frigid Cold Heads Towards the United States as Polar Vortex Lobe Turns South by the Next Weekend
Source: Severe Weather