What's in a Name? Post-Tropical Cyclone Sandy

By Helen Gibbons Nov. / Dec. 2012

in this issue:  previous story | next story

About an hour before Hurricane Sandy made landfall in New Jersey on the evening of October 29, 2012, the National Weather Service reclassified the storm as “Post-Tropical Cyclone Sandy.” The name change came as Sandy lost the characteristics of a strong tropical cyclone, or hurricane.

A tropical cyclone is a storm system with a warm core of low pressure surrounded by winds spiraling inward and upward. In the North Atlantic, strong tropical cyclones—with sustained winds of 74 miles per hour or higher—are called hurricanes. Tropical cyclones get their energy from warm ocean water: water evaporates from the ocean surface and then condenses as the saturated air rises. This condensation forms clouds and thunderstorms that become part of the tropical cyclone, and it releases heat energy that powers the winds of the cyclone.

In contrast, extratropical, or mid-latitude, cyclones get their energy not from warm ocean water but from horizontal temperature differences in the atmosphere. These low-pressure systems, with their associated warm fronts or cold fronts, are the most common type of storm in the United States. (For more information about tropical and extratropical cyclones, visit http://www.aoml.noaa.gov/hrd/tcfaq/tcfaqA.html.)

Above: NASA's Aqua satellite captured a visible image of Sandy's massive circulation on October 29 at 1820 UTC (2:20 p.m. EDT). Sandy covers 1.8 million square miles, from the Mid-Atlantic to the Ohio Valley, into Canada and New England. Image from NASA Goddard MODIS Rapid Response Team; for more information see http://www.nasa.gov/mission_pages/hurricanes/ archives/2012/h2012_Sandy.html. [larger version]

As Hurricane Sandy moved northward along the U.S. Atlantic coast, it met with a winter storm coming from the west and cold air coming down from Canada; interaction with these air masses hastened its transition to an extratropical cyclone. Because it began as a tropical cyclone, Sandy was designated not simply as an extratropical cyclone but as a “post-tropical” cyclone. While Sandy transitioned from a hurricane to a post-tropical cyclone as the center neared landfall, there was no change in expected impacts, including tropical-storm-force and hurricane-force winds, storm surge, heavy rain, inland flooding, and heavy snow. The cyclone’s intensity and enormous breadth inspired additional names, such as Frankenstorm and Superstorm Sandy.

USGS Scientists Predict, Measure Sandy's Impacts on the Coastal Landscape Nov. / Dec. 2012

Frequently Asked Questions: Hurricanes NOAA

Coastal Change Hazards: Hurricanes and Extreme Storms - Hurricane Sandy USGS

USGS Response to Hurricane Sandy USGS

in this issue:

previous story | next story

 
Nov. / Dec. 2012

print this issue

in this issue:

cover story:
Scientists Predict, Measure Sandy's Impacts

Post-Tropical Cyclone Sandy

Sediment Movement in the Northern Chandeleur Islands

Recovery Slows for California's Sea Otters

Mapping the Georges Bank Seabed

Native Youth in Science—Preserving Our Homelands

2011 Excellence in Partnering Award

Pacific Coastal and Marine Science Center Welcomes Andy O'Neill

Olivia Cheriton Joins Pacific Coastal and Marine Science Center

Nov. / Dec. Publications