The Extratropical Transition of Tropical Cyclones: Forecast Challenges, Current Understanding, and Future Directions
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Authors
Jones, Sarah C.
Harr, Patrick A.
Abraham, Jim
Bosart, Lance F.
Bowyer, Peter J.
Evans, Jenni L.
Hanley, Deborah E.
Hanstrum, Barry N.
Hart, Robert E.
Lalaurette, François
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Date of Issue
2003-12
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Abstract
A significant number of tropical cyclones move into the midlatitudes and transform into extratropical cyclones.
This process is generally referred to as extratropical transition (ET). During ET a cyclone frequently produces
intense rainfall and strong winds and has increased forward motion, so that such systems pose a serious threat
to land and maritime activities. Changes in the structure of a system as it evolves from a tropical to an extratropical
cyclone during ET necessitate changes in forecast strategies. In this paper a brief climatology of ET is given
and the challenges associated with forecasting extratropical transition are described in terms of the forecast
variables (track, intensity, surface winds, precipitation) and their impacts (flooding, bush fires, ocean response).
The problems associated with the numerical prediction of ET are discussed. A comprehensive review of the
current understanding of the processes involved in ET is presented. Classifications of extratropical transition
are described and potential vorticity thinking is presented as an aid to understanding ET. Further sections discuss
the interaction between a tropical cyclone and the midlatitude environment, the role of latent heat release,
convection and the underlying surface in ET, the structural changes due to frontogenesis, the mechanisms
responsible for precipitation, and the energy budget during ET. Finally, a summary of the future directions for
research into ET is given.
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Article
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Meteorology
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Sponsors
This paper arose from the First International Workshop on the Extratropical Transition of Tropical Cyclones, held in Kaufbeuren, Germany, in May 1999. The workshop was generously supported by the World Meteorological Organization and the U.S. Office of Naval Research.
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Weather and Forecasting, Volume 18, pp. 1052-1092, December 2003.
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This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.