For those of you who never studied meteorology, you might be a little alarmed when your social media feeds start exploding with scary-sounding weather terms like “bomb cyclone,” “bombogenesis” and “bombing out.”
Those are actual terms used by meteorologists, and they will likely apply to the massive wind and rain storm that is sweeping across the eastern United States on Wednesday. That’s because forecasters are expecting the storm system to rapidly intensify during a short time span — a process known as bombogenesis when it meets certain criteria.
Other folks in the weather world call this process “bombing out,” and some refer to this type of storm as a “bomb cyclone.”
In case you see a storm of social media posts today warning about these gloomy meteorological buzzwords, don’t be alarmed. Just keep your rain coat handy, be careful driving on wet roads, and take a few minutes to secure outdoor Halloween decorations that might blow away when the winds start gusting.
Here’s what these weather terms mean.
Technical definition
This is how the National Weather Service describes bombogenesis and bomb cyclones:
Bombogenesis, a popular term used by meteorologists, occurs when a mid-latitude cyclone rapidly intensifies, dropping at least 24 millibars over 24 hours. A millibar measures atmospheric pressure. This can happen when a cold air mass collides with a warm air mass, such as air over warm ocean waters. The formation of this rapidly strengthening weather system is a process called bombogenesis, which creates what is known as a bomb cyclone.
Our interpretation for non-weather geeks
Basically, any storm system in our region of the Atlantic that rapidly strengthens with a specific drop in pressure during a 24-hour period can be called a bomb cyclone. This is a common occurrence during the winter season, when nor’easters develop along the Atlantic coast and quickly intensify into a major snowstorm or blizzard.
“It tends to be more common in winter, but it’s not unheard of this time of year and not unheard of in the spring,” said Chad Shafer, a meteorologist at the National Weather Service’s regional forecast office in New Jersey.
Bomb cyclones rarely form in the summer, Shafer said, noting that this weather term is not used for hurricanes and other tropical storm systems that form in the tropics.
When hurricanes strengthen — when their central pressure drops and their wind speeds get stronger — the process is typically known as “rapid intensification.”
What is cyclogenesis?
Another weather term that has been popping up on social media this week is cyclogenesis, which is defined as “the formation or intensification of a cyclone or low-pressure storm system.”
If that sounds like what is happening with Wednesday’s coastal storm, that’s because it is. However, cyclogenesis is a more general term than bombogenesis, because it does not require a specific threshold of pressure dropping over a certain time frame, Shafer noted.
In short, bombogenesis is a specific type of cyclogenesis, and it has to meet the threshold of having its atmospheric pressure drop 24 millibars in 24 hours. As one weather website explains it, “Bombogenesis is cyclogenesis taken to the extreme.”
Is New Jersey getting hit with a bomb cyclone?
Wednesday’s storm system has already been getting stronger, but it is forecast to officially “bomb out” — reaching its strongest phase — when it is about 100 miles offshore from New Jersey and on its way up to New England.
So, New Jersey will not feel the full brunt of this bomb cyclone. However, the state will still get lashed by heavy rain and wind gusts as strong as 45 to 50 mph, particularly in and near the coastal areas.
And the strongest wind gusts will likely hit on Thursday, after the storm moves away from the Garden State.
Forecasters are expecting rain totals of about 1 inch in South Jersey, 1.5 to 2 inches in Central Jersey and 2 to 3 inches in North Jersey. The rain should end around 9 p.m. in southern areas of the state and by about 1 a.m. Thursday in the northeastern region.
A flash flood watch will be effect from this afternoon until late Wednesday evening for the state’s five northeastern counties, where forecasters say small streams could spill over their banks and streets, especially in urban areas with poor drainage.
Update (4:45 p.m.): A wind advisory was originally in effect just for the Jersey Shore region, but it has now been expanded to include the entire state. In most counties, the advisory runs from 6 p.m. Wednesday until 6 p.m. Thursday. In southern New Jersey, the wind advisory started at 3:45 p.m. Wednesday and runs through 6 p.m. Thursday.
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Len Melisurgo may be reached at LMelisurgo@njadvancemedia.com. Follow him on Twitter @LensReality or like him on Facebook. Find NJ.com on Facebook.