(This article originally appeared AccuWeather Global Weather Centre website.)
A beast of a bomb cyclone will take shape just off the coast of the northwestern United States and western Canada later this week, and AccuWeather forecasters say it will rival, in some aspects, the intensity of strong hurricanes from the Atlantic this season. The powerful storm will bring dangerous and damaging impacts up and down the West Coast, but the precipitation it will deliver to parts of California, Oregon and Washington is greatly needed.
The storm will have some tropical origins. Energy from former Severe Tropical Storm Namtheun, which churned over the western Pacific, will join forces with a non-tropical system sitting over the northern Pacific on Wednesday, according to AccuWeather Meteorologist Randy Adkins. Rapid strengthening will result. As the storm comes together a few hundred miles off the coasts of Washington and British Columbia, its intensification could easily surpass the criteria for bombogenesis.
Meteorologists define a bomb cyclone as a rapidly strengthening storm with a central pressure that plummets by 0.71 of an inch of mercury (24 millibars) or more within 24 hours. The process is referred to as bombogenesis. As the pressure drops rapidly in the center of the storm, air rushes in to replace the vacuum created in the atmosphere and can produce damaging winds.
The central pressure of the storm is forecast to dip to approximately 28 inches of mercury (948 millibars), putting the bomb cyclone at or even below the intensity level of Hurricane Larry, which was a long-lived and intense cyclone that churned across the Atlantic in early September. At peak strength, Larry was a major Category 3 hurricane with maximum sustained winds of 125 mph and higher gusts. Its central pressure dropped as low as 28.20 inches of mercury (955 millibars).
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