Extra-Tropical Transition

Extratropical Transition

Forecasting Impacts in Midlattitudes

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Introduction

 

Tropical cyclones feed off of the energy from the warm ocean below; they have only very small changes in temperature, and the environmental wind around the system is similar from its top to bottom (low wind shear). As they move out of the Tropics, they may encounter large changes in temperature, increasing wind shear and decreasing sea surface temperature which causes them to undergo a process known as Extratropical Transition.

Hurricane Ophelia 2017 Before Extratropical Transition
Hurricane Ophelia 2017

Satellite Image of Hurricane Ophelia 2017 After Exratropical Transition
Satellite Image of Hurricane Ophelia 2017 After Exratropical Transition

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Understanding Storm Structure & Evolution Improves Weather Forecasts

 

Hurricanes and tropical storms are complex phenomena that can grow and change as they move out of the tropics. The factors that influence storms, such as temperature, wind shear, and humidity can dictate those changes and change rapidly. We work to better understand the evolution of storms in order to improve forecasts and help minimize damage to life and property when storms do make landfall.

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Extratropical Transition can Lead to Decay or Rapid Intensification

 

These systems may produce intense rainfall, large waves, and hurricane-force winds, but the Extratropical Transition process remains poorly understood and forecast. Significant gaps exist in understanding changes in storm structure and in the forecasting of the ultimate outcome of Extratropical Transition – whether the system will decay or even rapidly intensify into a large and powerful extratopical cyclone.  In order to improve our understanding and forecasting of these events, targeted sampling of tropical cyclones undergoing Extratropical Transition are being made both with existing and new observing techniques.

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Creating A Weather-Ready Nation

With Storm Transition Research

Extratropical Transition can produce dangerous conditions, but not much is understood about how a storm transitions. This lack of understanding can result in poor forecasts. Our goal is to complete analyses of cases in which airborne data have been gathered and to use our new knowledge to improve the accuracy of these forecasts. To see our Extratropical Transition stories, visit the HRD Blog.

Remnant of Hillary after Reaching Cold Surface Water
Satellite Image Before Extratropical TransitionCategory 4 Hurricane Hilary

In Situ Sampling

As part of HRD’s Intensity Forecasting Experiment, we have undertaken a concerted effort to sample tropical cyclones undergoing Extratropical Transition with research aircraft.  Five Atlantic tropical cyclones have been sampled (Hurricanes Earl in 2010, Tomas in 2010, Sandy in 2012, Arthur in 2014 and Tropical Storm Karl in 2016). In addition, the NOAA P3 aircraft sampled two East Pacific Hurricanes (Patricia in 2015 and Hilary in 2011) before and during their weakening phases as they encountered strong vertical wind shear and a region of cold sea surface temperature, respectively.

Collecting Data from Hurricane Hurricane Sandy, 2012
Collecting Data from Hurricane Hurricane Sandy, 2012

What we Know about Extratropical Transition

Evans, C., K.M. Wood, S.D. Aberson, H.M. Archambault, S.M. Milrad, L.F. Bosart, K.L. Corbosiero, C.A. Davis, J.R. Dias Pinto, J. Doyle, C. Fogarty, T.J. Galarneau, C.M. Grams, K.S. Griffin, J. Gyakum, R.E. Hart, N. Kitabatake, H.S. Lentink, R. McTaggart-Cowan, W. Perrie, J.F. Quinting, C.A. Reynolds, M. Riemer, E.A. Ritchie, Y. Sun, and F. Zhang, 2017: The Extratropical Transition of Tropical Cyclones. Part I: Cyclone Evolution and Direct Impacts. Mon. Wea. Rev., 145, 4317–4344, https://doi.org/10.1175/MWR-D-17-0027.1

Abstract: Extratropical transition (ET) is the process by which a tropical cyclone, upon encountering a baroclinic environment and reduced sea surface temperature at higher latitudes, transforms into an extratropical cyclone. This process is influenced by, and influences, phenomena from the tropics to the midlatitudes and from the meso- to the planetary scales to extents that vary between individual events. Motivated in part by recent high-impact and/or extensively observed events such as North Atlantic Hurricane Sandy in 2012 and western North Pacific Typhoon Sinlaku in 2008, this review details advances in understanding and predicting ET since the publication of an earlier review in 2003. Methods for diagnosing ET…

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The Extratropical Transition of Tropical Cyclones. Part I: Cyclone Evolution and Direct Impacts

Evans, C., K.M. Wood, S.D. Aberson, H.M. Archambault, S.M. Milrad, L.F. Bosart, K.L. Corbosiero, C.A. Davis, J.R. Dias Pinto, J. Doyle, C. Fogarty, T.J. Galarneau, C.M. Grams, K.S. Griffin, J. Gyakum, R.E. Hart, N. Kitabatake, H.S. Lentink, R. McTaggart-Cowan, W. Perrie, J.F. Quinting, C.A. Reynolds, M. Riemer, E.A. Ritchie, Y. Sun, and F. Zhang, 2017: The Extratropical Transition of Tropical Cyclones. Part I: Cyclone Evolution and Direct Impacts. Mon. Wea. Rev., 145, 4317–4344, https://doi.org/10.1175/MWR-D-17-0027.1

Abstract: Extratropical transition (ET) is the process by which a tropical cyclone, upon encountering a baroclinic environment and reduced sea surface temperature at higher latitudes, transforms into an extratropical cyclone. This process is influenced by, and influences, phenomena from the tropics to the midlatitudes and from the meso- to the planetary scales to extents that vary between individual events. Motivated in part by recent high-impact and/or extensively observed events such as North Atlantic Hurricane Sandy in 2012 and western North Pacific Typhoon Sinlaku in 2008, this review details advances in understanding and predicting ET since the publication of an earlier review in 2003. Methods for diagnosing ET…

Read Full Paper

Extratropical_Transition

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Atlantic Hurricanes

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| Sim D. Aberson, Ph.D.

Principal Investigator

If you would like more information on the this project, please contact Sim Aberson, Principal Investigator of this project.