Rapid deepening in the context of "Typhoon Yunya (1991)"

Explosive cyclogenesis (also referred to as a weather bomb, meteorological bomb, explosive development, bomb cyclone, or bombogenesis) is the rapid deepening of an extratropical cyclonic low-pressure area. The change in pressure needed to classify something as explosive cyclogenesis is latitude dependent. For example, at 60° latitude, explosive cyclogenesis occurs if the central pressure decreases by 24 millibars (0.71 inHg) or more in 24 hours. This is a predominantly maritime, winter event, but also occurs in continental settings. This process is the extratropical equivalent of the tropical rapid deepening. Although their cyclogenesis is entirely different from that of tropical cyclones, bomb cyclones can produce winds of 74 to 95 mph (120 to 155 km/h), the same order as the first categories of the Saffir–Simpson scale, and yield heavy precipitation. Even though only a minority of bomb cyclones become this strong, some weaker ones can also cause significant damage.

Hurricane Bertha was the longest-lived Atlantic tropical cyclone on record during July, as well as the furthest east system to attain tropical storm intensity during the month. The second named storm, first hurricane, and first major hurricane of the active 2008 season, Bertha developed into a tropical depression on July 3 from a tropical wave that departed western Africa two days prior. On a west-northwest to northwest track, the depression intensified into Tropical Storm Bertha six hours formation and ultimately attained hurricane intensity on July 7. A period of rapid deepening brought the cyclone to its peak as a Category 3 hurricane with winds of 125 mph (205 km/h) late that afternoon. Changes in wind shear and the storm's internal structure allowed Bertha to fluctuate in intensity over the next week as it passed very near Bermuda, but a track over cooler waters eventually caused the system to become an extratropical cyclone by July 20. It continued northeast and was absorbed by another low near Iceland the following day. Rough surf propelled by Bertha killed three people along the East Coast of the United States; hundreds of other swimmers were injured and/or required rescuing. In Bermuda, some streets were flooded and strong gusts cut power to approximately 7,500 homes; only minor damage was observed.