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

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 in reanalysis, observational, and model-forecast datasets are discussed. New climatologies for the eastern North Pacific and southwest Indian Oceans are presented alongside updates to western North Pacific and North Atlantic Ocean climatologies. Advances in understanding and, in some cases, modeling the direct impacts of ET-related wind, waves, and precipitation are noted. Improved understanding of structural evolution throughout the transformation stage of ET fostered in large part by novel aircraft observations collected in several recent ET events is highlighted. Predictive skill for operational and numerical model ET-related forecasts is discussed along with environmental factors influencing posttransition cyclone structure and evolution. Operational ET forecast and analysis practices and challenges are detailed. In particular, some challenges of effective hazard communication for the evolving threats posed by a tropical cyclone during and after transition are introduced. This review concludes with recommendations for future work to further improve understanding, forecasts, and hazard communication.

Toward High‐Resolution Period‐Dependent Seismic Monitoring of Tropical Cyclones

“…The seismic sources are located in the wake of the typhoon, and they follow the typhoon track ( Figure 1). These turning points are located between 30 • N and 40 • N, corresponding to its tropical-extratropical transition (e.g., Evans et al, 2017). The azimuth of the track (red dots) shows that the typhoon turned eastward (azimuth larger than 180 • ) after 5 September 2006, at 6 a.m.…”

Simulation of Wave‐Current Interactions Under Hurricane Conditions Using an Unstructured‐Grid Model: Impacts on Ocean Waves

“…Compared to tropical cyclones as considered by Chen et al (2013c) and Fan et al (2009aFan et al ( , 2009bFan et al ( , 2010, extratropical hurricanes can undergo extratropical intensification; this may occur as tropical cyclones move poleward, encountering the more baroclinic environment of the midlatitudes. This process is called extratropical transition (Evans et al, 2017). Thus, extratropical hurricanes tend to develop baroclinic characteristics becoming larger in spatial extent and their propagation speeds tend to accelerate.…”

A Metric for Rainfall Asymmetry in Recurving Tropical Cyclones

“…In subregion IIIa, the TC warm core begins to disperse in the upper-levels while the cases in IIIb have fully lost their tropical structure (Figure 5d). The TCs in IIIa are most likely still undergoing ET while the TCs in IIIb have completed ET and are Ex-TCs (Evans et al, 2017).…”

“…The structural changes that occur to a TC as it recurves into the midlatitudes and undergoes ET have been documented in a number of studies (Evans et al, 2017;Jones et al, 2003) including the cyclone phase-space (CPS; Hart, 2003), frontogenesis , and potential vorticity (Kofron et al, 2010a(Kofron et al, , 2010b. The structural changes that occur to a TC as it recurves into the midlatitudes and undergoes ET have been documented in a number of studies (Evans et al, 2017;Jones et al, 2003) including the cyclone phase-space (CPS; Hart, 2003), frontogenesis , and potential vorticity (Kofron et al, 2010a(Kofron et al, , 2010b.…”

“…Rainfall asymmetries can also arise after recurvature of the TC as it undergoes extratropical transition (ET). The structural changes that occur to a TC as it recurves into the midlatitudes and undergoes ET have been documented in a number of studies (Evans et al, 2017;Jones et al, 2003) including the cyclone phase-space (CPS; Hart, 2003), frontogenesis , and potential vorticity (Kofron et al, 2010a(Kofron et al, , 2010b.…”