Rapid deepening

Rapid deepening, also know as rapid intensification, is a meteorological condition that occurs when the minimum sea-level atmospheric pressure of a tropical cyclone decreases drastically in a short period of time. The National Weather Service describes rapid deepening as a decrease of 42 millibars in less than 24 hours.cite web | author=National Hurricane Center | date = January 17, 2006 | title=Glossary of NHC/TPC Terms | publisher=NOAA | accessdate=2006-06-07 | url=http://www.nhc.noaa.gov/aboutgloss.shtml] However, this phrase is liberally applied to most storms undergoing rapid intensification.

Necessary conditions

In order for rapid deepening to occur, several conditions must be in place. Water temperatures must be extremely warm (near or above 30°C, 86°F), and water of this temperature must be sufficiently deep such that waves do not churn deeper cooler waters up to the surface. Wind shear must be low; when wind shear is high, the convection and circulation in the cyclone will be disrupted. Usually, an anticyclone in the upper layers of the troposphere above the storm must be present as well — for extremely low surface pressures to develop, air must be rising very rapidly in the eyewall of the storm, and an upper-level anticyclone helps channel this air away from the cyclone efficiently.Fact|date=February 2007

Explosive intensification

Explosive intensification is a more extreme case of rapid deepening that involves a tropical cyclone deepening at a rate of at least 2.5 mbar per hour for a minimum of 12 hours. Explosive intensification is rather rare, as conditions must be exceedingly favorable for cyclone intensification. Explosive intensification occurs regularly in the West Pacific basin, with the greatest frequency off the north coast of Australia; however, it has occurred numerous times in the Atlantic basin, as with 2008's Hurricane Ike with the hurricane undergoing a 24 millibar pressure drop in 3 hours. However, this is not a true explosive intesification because this deepening did not last for 12 hours

pecific instances

In 2004, Hurricane Charley was approaching the west coast of Florida as a category two storm on the Saffir-Simpson scale of hurricane strength. When just off the coast, however, its sustained winds rapidly increased from 110 to 150 mph (along with a pressure drop from 965 to 941 mbar) in only three hours. Charley caused unprecedented destruction in the Punta Gorda area, and inflicted major damage across the state of Florida.cite web | author=National Hurricane Center | year=2004 | title=Tropical Cyclone Report: Hurricane Charley | publisher=NOAA | date= January 5, 2005 | accessdate=2006-06-07 | url=http://www.nhc.noaa.gov/2004charley.shtml]

In 2005, the minimum central pressure of Hurricane Wilma dropped from 981 to 882 mbar in 24 hours, including an incredible drop of 53 mbar in less than 6 hours. This is by far the fastest intensification of any Atlantic hurricane, and possibly the fastest intensification for any system in recorded history.cite web | author=National Hurricane Center | date = January 12, 2006 | title=Tropical Cyclone Report: Hurricane Wilma | publisher=NOAA | accessdate=2006-06-07 | url=http://www.nhc.noaa.gov/pdf/TCR-AL252005_Wilma.pdf | format=PDF] Typhoon Forrest in 1983 may have strengthened faster, deepening from 976 to 876 mbar in just under 24 hours, but pressure estimates for this storm were much less accurate. [cite web | last = Landsea | first = Chris | authorlink=Christopher Landsea | title=FAQ: Which tropical cyclone intensified the fastest? | publisher=Atlantic Oceanographic and Meteorological Laboratory | accessdate=2006-06-07 | url=http://www.aoml.noaa.gov/hrd/tcfaq/E2.html] 2005 was also notable in that two other storms, Katrina and Rita, also underwent episodes of extremely rapid intensification.

In 2006, the minimum central pressure of Typhoon Chebi in the Western Pacific dropped 75 mbar in 24 hours, including a 60 mbar pressure drop in 6 hours, as it intensified from a tropical storm to a category four equivalent typhoon in one advisory. [http://agora.ex.nii.ac.jp/digital-typhoon/summary/wnp/l/200620.html.en]

In 2008, Hurricane Ike in the Atlantic basin was upgraded from a tropical storm to a Category 4 hurricane in just twelve hours, only a few days after Hurricane Gustav underwent a similar episode of rapid intensification.

References

ee also

*Tropical cyclone
*bomb (meteorology)