The Unexpected Rapid Intensification of Tropical Cyclones in Moderate Vertical Wind Shear. Part I: Overview and Observations

Abstract A satellite-based investigation is performed of a class of tropical cyclones (TCs) that unexpectedly undergo rapid intensification (RI) in moderate vertical wind shear between 5 and 10 m s−1 calculated as 200–850-hPa shear. This study makes use of both infrared (IR; 11 μm) and water vapor (WV; 6.5 μm) geostationary satellite data, the Statistical Hurricane Prediction Intensity System (SHIPS), and model reanalyses to highlight commonalities of the six TCs. The commonalities serve as predictive guides for forecasters and common features that can be used to constrain and verify idealized modeling studies. Each of the TCs exhibits a convective cloud structure that is identified as a tilt-modulated convective asymmetry (TCA). These TCAs share similar shapes, upshear-relative positions, and IR cloud-top temperatures (below −70°C). They pulse over the core of the TC with a periodicity of between 4 and 8 h. Using WV satellite imagery, two additional features identified are asymmetric warming/drying upshear of the TC relative to downshear, as well as radially thin arc-shaped clouds on the upshear side. The WV brightness temperatures of these arcs are between −40° and −60°C. All of the TCs are sheared by upper-level anticyclones, which limits the strongest environmental winds to near the tropopause.

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The Influence of Environments on the Intensity Change of Typhoon Soudelor

Atmosphere ◽

10.3390/atmos12020162 ◽

2021 ◽

Vol 12 (2) ◽

pp. 162

Author(s):

Leo Oey ◽

Yuchen Lin

Keyword(s):

Tropical Cyclones ◽

Wind Shear ◽

Vertical Wind Shear ◽

Intensity Variation ◽

Vertical Wind ◽

Intensity Change ◽

Rapid Intensification ◽

Philippine Sea ◽

Anomalous Anticyclone ◽

Upper Level

Previous studies have shown that background oceanic and atmospheric environments can influence not only the formation but also the intensity of tropical cyclones. Typhoon Soudelor in August 2015 is notable in that it underwent two rapid intensifications as the storm passed over the Philippine Sea where the 26 °C isotherm (Z26) was deeper than 100 m and warm eddies abounded. At the same time, prior to the storm’s arrival, an anomalous upper-level anticyclone developed south of Japan and created a weakened vertical wind shear (Vs) environment that extended into the Philippine Sea. This study examines how the rapid intensification of Typhoon Soudelor may be related to the observed variations of Z26, Vs and other environmental fields as the storm crossed over them. A regression analysis indicates that the contribution to Soudelor’s intensity variation from Vs is the largest (62%), followed by Z26 (27%) and others. Further analyses using composites then indicate that the weak vertical wind shear produced by the aforementioned anomalous anticyclone is a robust feature in the western North Pacific during the developing summer of strong El Ninos with Oceanic Nino Index (ONI) > 1.5.

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The Unexpected Rapid Intensification of Tropical Cyclones in Moderate Vertical Wind Shear. Part III: Outflow–Environment Interaction

Monthly Weather Review ◽

10.1175/mwr-d-18-0370.1 ◽

2019 ◽

Vol 147 (8) ◽

pp. 2919-2940 ◽

Cited By ~ 7

Author(s):

David R. Ryglicki ◽

James D. Doyle ◽

Daniel Hodyss ◽

Joshua H. Cossuth ◽

Yi Jin ◽

...

Keyword(s):

Wind Shear ◽

Vertical Wind Shear ◽

Environmental Flow ◽

Vertical Wind ◽

Environment Interaction ◽

Rapid Intensification ◽

Field Matching ◽

Upper Level ◽

Bernoulli Flow ◽

Dynamic High Pressure

Abstract Interactions between the upper-level outflow of a sheared, rapidly intensifying tropical cyclone (TC) and the background environmental flow in an idealized model are presented. The most important finding is that the divergent outflow from convection localized by the tilt of the vortex serves to divert the background environmental flow around the TC, thus reducing the local vertical wind shear. We show that this effect can be understood from basic theoretical arguments related to Bernoulli flow around an obstacle. In the simulation discussed, the environmental flow diversion by the outflow is limited to 2 km below the tropopause in the 12–14-km (250–150 hPa) layer. Synthetic water vapor satellite imagery confirms the presence of upshear arcs in the cloud field, matching satellite observations. These arcs, which exist in the same layer as the outflow, are caused by slow-moving wave features and serve as visual markers of the outflow–environment interface. The blocking effect where the outflow and the environmental winds meet creates a dynamic high pressure whose pressure gradient extends nearly 1000 km upwind, thus causing the environmental winds to slow down, to converge, and to sink. We discuss these results with respect to the first part of this three-part study, and apply them to another atypical rapid intensification hurricane: Matthew (2016).

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The Unexpected Rapid Intensification of Tropical Cyclones in Moderate Vertical Wind Shear. Part II: Vortex Tilt

Monthly Weather Review ◽

10.1175/mwr-d-18-0021.1 ◽

2018 ◽

Vol 146 (11) ◽

pp. 3801-3825 ◽

Cited By ~ 12

Author(s):

David R. Ryglicki ◽

James D. Doyle ◽

Yi Jin ◽

Daniel Hodyss ◽

Joshua H. Cossuth

Keyword(s):

Tropical Cyclones ◽

Wind Shear ◽

Deep Convection ◽

Vertical Wind Shear ◽

Vertical Wind ◽

Rapid Intensification ◽

Model Simulations ◽

Observational Analysis ◽

Idealized Model ◽

Cold Anomaly

Abstract We investigate a class of tropical cyclones (TCs) that undergo rapid intensification (RI) in moderate vertical wind shear through analysis of a series of idealized model simulations. Two key findings derived from observational analysis are that the average 200–850-hPa shear value is 7.5 m s−1 and that the TCs displayed coherent cloud structures, deemed tilt-modulated convective asymmetries (TCA), which feature pulses of deep convection with periods of between 4 and 8 h. Additionally, all of the TCs are embedded in an environment that is characterized by shear associated with anticyclones, a factor that limits depth of the strongest environmental winds in the vertical. The idealized TC develops in the presence of relatively shallow environmental wind shear of an anticyclone. An analysis of the TC tilt in the vertical demonstrates that the source of the observed 4–8-h periodicity of the TCAs can be explained by smaller-scale nutations of the tilt on the longer, slower upshear precession. When the environmental wind shear occurs over a deeper layer similar to that of a trough, the TC does not develop. The TCAs are characterized as collections of updrafts that are buoyant throughout the depth of the TC since they rise into a cold anomaly caused by the tilting vortex. At 90 h into the simulation, RI occurs, and the tilt nutations (and hence the TCAs) cease to occur.

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Changes in Characteristics of Rapidly Intensifying Western North Pacific Tropical Cyclones Related to Climate Regime Shifts

Journal of Climate ◽

10.1175/jcli-d-18-0029.1 ◽

2018 ◽

Vol 31 (19) ◽

pp. 8163-8179 ◽

Cited By ~ 22

Author(s):

Haikun Zhao ◽

Xingyi Duan ◽

G. B. Raga ◽

Philip J. Klotzbach

Keyword(s):

Tropical Cyclones ◽

North Pacific ◽

Wind Shear ◽

Western North Pacific ◽

Regime Shift ◽

Vertical Wind Shear ◽

Vertical Wind ◽

Rapid Intensification ◽

Climate Regime ◽

Climate Regime Shift

A significant increase in the proportion of tropical cyclones undergoing rapid intensification at least once during their lifetime (RITCs) over the western North Pacific (WNP) is observed since 1998 when an abrupt climate regime shift occurred. Changes of large-scale atmospheric and oceanic conditions affecting TC activity are compared between two subperiods: one before and one since 1998. Results suggest that both a significant decrease in the number of TCs and a nearly unchanged number of RITCs since 1998 caused a significant increase in the frequency of RITCs. The decrease in TC numbers is likely driven by considerably increased vertical wind shear and decreased low-level vorticity. In contrast, the unchanged RITC counts and thus increased ratio of RITCs during the recent decades are largely attributed to the dominance of a more conducive ocean environment with increased TC heat potential and warmer sea surface temperature anomalies. These associated decadal changes are closely associated with the recent climate regime shift. During the recent decades with a mega–La Niña–like pattern, stronger easterly trade winds have caused increased vertical wind shear and a weakened monsoon trough, thus hampering TC formation ability over the WNP. In addition, a steeper thermocline slope that hampered the eastward migration of warm water along the equatorial Pacific has generated a more favorable thermodynamic environment supporting TC rapid intensification over the WNP.

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Comments on “Multiscale Structure and Evolution of Hurricane Earl (2010) during Rapid Intensification”

Monthly Weather Review ◽

10.1175/mwr-d-16-0301.1 ◽

2017 ◽

Vol 145 (4) ◽

pp. 1565-1571 ◽

Cited By ~ 5

Author(s):

Russell L. Elsberry ◽

Myung-Sook Park

Keyword(s):

Vortex Structure ◽

Wind Shear ◽

Environmental Control ◽

Vertical Wind Shear ◽

Special Kind ◽

Vertical Wind ◽

Rapid Intensification ◽

Structure Changes ◽

Maximum Period ◽

Upper Level

Abstract This comment addresses the Tropical Storm (TS) Earl upper-level vortex structure changes during a critical stage leading to the onset of rapid intensification as described by Rogers et al. Whereas the first NOAA WP-3D mission in TS Earl provided evidence of a shallow, broad vortex structure, the second WP-3D mission just 12 h later documented a deep, vertically stacked vortex undergoing rapid intensification. The authors attribute this vortex structure change to vertical alignment processes between the low-level Earl vortex and an upper-tropospheric mesoscale vortex about 50 km to the east in the mission 1 analyses. An alternate environmental control explanation is proposed in which a special kind of upper-tropospheric vertical wind shear (VWS) associated with the outflow of Hurricane Danielle to the northwest of TS Earl is the primary factor. Two estimates of the vertical wind shear changes are interpreted relative to the diurnal convective maximum/minimum to explain how the shallow vortex during mission 1 may have been created. It is proposed that the vigorous convection over sea surface temperatures of about 30°C during the diurnal convective maximum period between mission 1 and mission 2 was able to offset the moderate VWS as Hurricane Danielle had moved farther away from Earl. Thus, an explanation for the vertically stacked TS Earl vortex observed during mission 2 in terms of an environmental VWS modulation of the diurnally varying convective processes is proposed as an alternative to a vortex realignment.

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Observed Processes Underlying the Favorable Vortex Repositioning Early in the Development of Hurricane Dorian (2019).

Monthly Weather Review ◽

10.1175/mwr-d-21-0069.1 ◽

2021 ◽

Author(s):

George R. Alvey ◽

Michael Fischer ◽

Paul Reasor ◽

Jonathan Zawislak ◽

Robert Rogers

Keyword(s):

Wind Shear ◽

Inner Core ◽

Doppler Radar ◽

Deep Convection ◽

Vertical Wind Shear ◽

Vertical Wind ◽

Rapid Intensification ◽

In Situ Data ◽

Upper Level

AbstractDorian’s evolution from a weak, disorganized tropical storm to a rapidly intensifying hurricane is documented through a unique multi-platform synthesis of NOAA’s P-3 tail-Doppler radar, airborne in situ data, and Meteo-France’s Martinique and Guadeloupe ground radar network. Dorian initially struggled to intensify with a misaligned vortex in moderate mid-tropospheric vertical wind shear that also allowed detrimental impacts from dry air near the inner core. Despite vertical wind shear eventually decreasing to less than 5 m/s and an increasingly symmetric distribution of stratiform precipitation, the vortex maintained its misalignment with asymmetric convection for 12 hours. Then, as the low-level circulation (LLC) approached St. Lucia, deep convection near the LLC’s center dissipated, the LLC broadened, and precipitation expanded radially outwards from the center temporally coinciding with the diurnal cycle. Convection then developed farther downtilt within a more favorable, humid environment and deepened appreciably at least partially due to interaction with Martinique. A distinct repositioning of the LLC towards Martinique is induced by spin-up of a mesovortex into a small, compact LLC.It is hypothesized that this somewhat atypical reformation event and the repositioning of the vortex into a more favorable environment, farther from detrimental dry mid-tropospheric air, increased its favorability for the rapid intensification that subsequently ensued. Although the repositioning resulted in tilt reducing to less than the scale of the vortex itself, the pre-existing broad mid-upper level cyclonic envelope remained intact with continued misalignment observed between the mid-level center and repositioned LLC even during the early stages of rapid intensification.

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Simulation of Rapid Intensification of Super Typhoon Lekima (2019). Part I: Evolution Characteristics of Asymmetric Convection Under Upper-Level Vertical Wind Shear

Frontiers in Earth Science ◽

10.3389/feart.2021.739507 ◽

2021 ◽

Vol 9 ◽

Author(s):

Qijun Huang ◽

Xuyang Ge ◽

Melinda Peng

Keyword(s):

Wind Shear ◽

Inner Core ◽

Thermal Structure ◽

Deep Convection ◽

Vertical Wind Shear ◽

Vertical Wind ◽

Rapid Intensification ◽

Super Typhoon ◽

Storm Center ◽

Upper Level

The role of the upper-level vertical wind shear (VWS) on the rapid intensification (RI) of super typhoon Lekima (2019) is investigated with a high-resolution numerical simulation. Our simulation shows that under moderate upper-level easterly VWS, the tilting-induced convective asymmetry is transported from the initially downshear quadrant to the upshear quadrant and wrapped around the storm center by the cyclonic flow of the storm while moving inward. This process enhances upward motions at the upshear flank and creates upper-level divergent flow. As such, the establishment of outflow acts against the environmental flow to reduce the VWS, allowing vertical alignment of the storm. The organized outflow plays an important role in sustaining the inner-core deep convection by modulating the environmental upper-level thermal structure. Accompanying deep convective bursts (CBs), cold anomalies are generated in the tropopause layer due to the adiabatic cooling by the upward motion and radiative process associated with the cloud anvil. Physically, cold anomalies at the tropopause locally destabilize the atmosphere and enhance the convections and the secondary circulation. The CBs continue to develop episodically through this process as they wrap around the storm center to form a symmetric eyewall. The results suggest that deep convections are capable of reducing the upper-level VWS, promoting the development of upper-level outflow. Lekima overcame the less favorable environment and eventually intensified to become a super typhoon.

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Influence of Environmental Vertical Wind Shear on the Intensity of Hurricane-Strength Tropical Cyclones in the Australian Region

Monthly Weather Review ◽

10.1175/mwr3041.1 ◽

2005 ◽

Vol 133 (12) ◽

pp. 3644-3660 ◽

Cited By ~ 65

Author(s):

Linda A. Paterson ◽

Barry N. Hanstrum ◽

Noel E. Davidson ◽

Harry C. Weber

Keyword(s):

Tropical Cyclones ◽

Wind Shear ◽

Time Lag ◽

Vertical Wind Shear ◽

Vertical Wind ◽

Intensity Change ◽

Negative Effects ◽

Australian Region ◽

Upper Level ◽

The Impact

Abstract NCEP–NCAR reanalyses have been used to investigate the impact of environmental wind shear on the intensity change of hurricane-strength tropical cyclones in the Australian region. A method of removing a symmetric vortex from objective analyses is used to isolate the environmental flow. A relationship between wind shear and intensity change is documented. Correlations between wind shear and intensity change to 36 h are of the order of 0.4. Typically a critical wind shear value of ∼10 m s−1 represents a change from intensification to dissipation. Wind shear values of less than ∼10 m s−1 favor intensification, with values between ∼2 and 4 m s−1 favoring rapid intensification. Shear values greater than ∼10 m s−1 are associated with weakening, with values greater than 12 m s−1 favoring rapid weakening. There appears to be a time lag between the onset of increased vertical wind shear and the onset of weakening, typically between 12 and 36 h. A review of synoptic patterns during intensification-weakening cycles revealed the juxtaposition of a low-level anticyclone on the poleward side of the storm and an approaching 200-hPa trough to the west. In most cases, intensification commences under weak shear with the approach of the trough, but just prior to the onset of high shear. Further, based on described cases when wind shear was weak but no intensification occurred, it is suggested that weak shear is a necessary but not a sufficient condition for intensification. It is illustrated here that the remote dynamical influence of upper-level potential vorticity anomalies may offset the negative effects of environmental shear.

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Effects of Vertical Wind Shear on the Predictability of Tropical Cyclones

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-12-0133.1 ◽

2013 ◽

Vol 70 (3) ◽

pp. 975-983 ◽

Cited By ~ 120

Author(s):

Fuqing Zhang ◽

Dandan Tao

Keyword(s):

Tropical Cyclone ◽

Tropical Cyclones ◽

Small Amplitude ◽

Wind Shear ◽

Random Noise ◽

Vertical Wind Shear ◽

Vertical Wind ◽

Small Scale ◽

Rapid Intensification ◽

Moist Convection

Abstract Through cloud-resolving simulations, this study examines the effect of vertical wind shear and system-scale flow asymmetry on the predictability of tropical cyclone (TC) intensity during different stages of the TC life cycle. A series of ensemble experiments is performed with varying magnitudes of vertical wind shear, each initialized with an idealized weak TC-like vortex, with small-scale, small-amplitude random perturbations added to the initial conditions. It is found that the environmental shear can significantly affect the intrinsic predictability of tropical cyclones, especially during the formation and rapid intensification stage. The larger the vertical wind shear, the larger the uncertainty in the intensity forecast, primarily owing to the difference in the timing of rapid intensification. In the presence of environmental shear, initial random noise may result in changes in the timing of rapid intensification by as much as 1–2 days through the randomness (and chaotic nature) of moist convection. Upscale error growth from differences in moist convection first alters the tilt amplitude and angle of the incipient tropical storms, which leads to significant differences in the timing of precession and vortex alignment. During the precession process, both the vertical tilt of the storm and the effective (local) vertical wind shear are considerably decreased after the tilt angle reaches 90° to the left of the environmental shear. The tropical cyclone intensifies immediately after the tilt and the effective local shear reach their minima. In some instances, small-scale, small-amplitude random noise may also limit the intensity predictability through altering the timing and strength of the eyewall replacement cycle.

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The Intensity- and Size-Dependent Response of Tropical Cyclones to Increasing Vertical Wind Shear

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-21-0126.1 ◽

2021 ◽

Author(s):

Peter M. Finocchio ◽

Rosimar Rios-Berrios

Keyword(s):

Wind Field ◽

Wind Shear ◽

Diabatic Heating ◽

Inner Core ◽

Potential Temperature ◽

Vertical Wind Shear ◽

Vertical Wind ◽

Rapid Intensification ◽

Vertical Coupling ◽

Tangential Wind

AbstractThis study describes a set of idealized simulations in which westerly vertical wind shear increases from 3 to 15 m s−1 at different stages in the lifecycle of an intensifying tropical cyclone (TC). The TC response to increasing shear depends on the intensity and size of the TC’s tangential wind field when shear starts to increase. For a weak tropical storm, increasing shear decouples the vortex and prevents intensification. For Category 1 and stronger storms, increasing shear causes a period of weakening during which vortex tilt increases by 10–30 km before the TCs reach a near-steady Category 1–3 intensity at the end of the simulations. TCs exposed to increasing shear during or just after rapid intensification tend to weaken the most. Backward trajectories reveal a lateral ventilation pathway between 8–11 km altitude that is capable of reducing equivalent potential temperature in the inner core of these TCs by nearly 2°C. In addition, these TCs exhibit large reductions in diabatic heating inside the radius of maximum winds (RMW) and lower-entropy air parcels entering downshear updrafts from the boundary layer, which further contributes to their substantial weakening. The TCs exposed to increasing shear after rapid intensification and an expansion of the outer wind field reach the strongest near-steady intensity long after the shear increases because of strong vertical coupling that prevents the development of large vortex tilt, resistance to lateral ventilation through a deep layer of the middle troposphere, and robust diabatic heating within the RMW.

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