On the rapid intensification of Hurricane
            Wilma
            (2005). Part IV: Inner‐core dynamics during the steady radius of maximum wind stage

<p>Recent studies show that some hurricanes may undergo rapid intensification (RI) without contracting the radius of maximum wind (RMW). A cloud-resolving WRF-prediction of Hurricane Wilma (2005) is used herein to examine what controls the RMW contraction and how a hurricane could undergo RI without contraction. Results show that the processes controlling the RMW contraction are different within and above the planetary boundary layer (PBL). In the PBL, radial inflows contribute to contraction, with frictional dissipation acting as an inhibiting factor. Above the PBL, radial outflows and vertical motion govern the RMW contraction, with the former inhibiting it. A budget analysis of absolute angular momentum (AAM) shows that the radial AAM flux convergence is the major process accounting for the spinup of the maximum rotation, while the vertical flux divergence of AAM and the frictional sink in the PBL oppose the spinup. During the RI stage with no RMW contraction, the local AAM tendencies in the eyewall are smaller in magnitude and narrower in width than those during the contracting RI stage. In addition, the AAM following the time-dependent RMW decreases with time in the PBL and remains nearly constant aloft during the contracting stage, whereas it increases during the non-contracting stage. These results reveal different constraints for the RMW contraction and RI, and help explain why a hurricane vortex can still intensify after the RMW ceases contraction</p>

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On the Rapid Intensification of Hurricane Wilma (2005). Part II: Convective Bursts and the Upper-Level Warm Core

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-12-062.1 ◽

2013 ◽

Vol 70 (1) ◽

pp. 146-162 ◽

Cited By ~ 124

Author(s):

Hua Chen ◽

Da-Lin Zhang

Keyword(s):

Inner Core ◽

Static Stability ◽

Rapid Intensification ◽

Important Ingredient ◽

High Resolution Data ◽

Hurricane Wilma ◽

Warm Core ◽

Convective Bursts ◽

Upper Level ◽

The Relationship

Abstract Previous studies have focused mostly on the roles of environmental factors in the rapid intensification (RI) of tropical cyclones (TCs) because of the lack of high-resolution data in inner-core regions. In this study, the RI of TCs is examined by analyzing the relationship between an upper-level warm core, convective bursts (CBs), sea surface temperature (SST), and surface pressure falls from 72-h cloud-permitting predictions of Hurricane Wilma (2005) with the finest grid size of 1 km. Results show that both the upper-level inertial stability increases and static stability decreases sharply 2–3 h prior to RI, and that the formation of an upper-level warm core, from the subsidence of stratospheric air associated with the detrainment of CBs, coincides with the onset of RI. It is found that the development of CBs precedes RI, but most subsidence warming radiates away by gravity waves and storm-relative flows. In contrast, many fewer CBs occur during RI, but more subsidence warming contributes to the balanced upper-level cyclonic circulation in the warm-core (as intense as 20°C) region. Furthermore, considerable CB activity can still take place in the outer eyewall as the storm weakens during its eyewall replacement. A sensitivity simulation, in which SSTs are reduced by 1°C, shows pronounced reductions in the upper-level warm-core intensity and CB activity. It is concluded that significant CB activity in the inner-core regions is an important ingredient in generating the upper-level warm core that is hydrostatically more efficient for the RI of TCs, given all of the other favorable environmental conditions.

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On the Rapid Intensification of Hurricane Wilma (2005). Part I: Model Prediction and Structural Changes

Weather and Forecasting ◽

10.1175/waf-d-11-00001.1 ◽

2011 ◽

Vol 26 (6) ◽

pp. 885-901 ◽

Cited By ~ 60

Author(s):

Hua Chen ◽

Da-Lin Zhang ◽

James Carton ◽

Robert Atlas

Keyword(s):

Model Prediction ◽

Structural Changes ◽

Inner Core ◽

Initial Conditions ◽

Single Case ◽

Inversion Layer ◽

Rapid Intensification ◽

Structural Variations ◽

Hurricane Wilma ◽

Intensity Changes

Abstract In this study, a 72-h cloud-permitting numerical prediction of Hurricane Wilma (2005), covering its initial 18-h spinup, an 18-h rapid intensification (RI), and the subsequent 36-h weakening stage, is performed using the Weather Research Forecast Model (WRF) with the finest grid length of 1 km. The model prediction uses the initial and lateral boundary conditions, including the bogus vortex, that are identical to the Geophysical Fluid Dynamics Laboratory’s then-operational data, except for the time-independent sea surface temperature field. Results show that the WRF prediction compares favorably in many aspects to the best-track analysis, as well as satellite and reconnaissance flight-level observations. In particular, the model predicts an RI rate of more than 4 hPa h−1 for an 18-h period, with the minimum central pressure of less than 889 hPa. Of significance is that the model captures a sequence of important inner-core structural variations associated with Wilma’s intensity changes, namely, from a partial eyewall open to the west prior to RI to a full eyewall at the onset of RI, rapid eyewall contraction during the initial spinup, the formation of double eyewalls with a wide moat area in between during the most intense stage, and the subsequent eyewall replacement leading to the weakening of Wilma. In addition, the model reproduces the boundary layer growth up to 750 hPa with an intense inversion layer above in the eye. Recognizing that a single case does not provide a rigorous test of the model predictability due to the stochastic nature of deep convection, results presented herein suggest that it is possible to improve forecasts of hurricane intensity and intensity changes, and especially RI, if the inner-core structural changes and storm size could be reasonably predicted in an operational setting using high-resolution cloud-permitting models with realistic initial conditions and model physical parameterizations.

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On the Rapid Intensification of Hurricane Wilma (2005). Part III: Effects of Latent Heat of Fusion

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-14-0386.1 ◽

2015 ◽

Vol 72 (10) ◽

pp. 3829-3849 ◽

Cited By ~ 18

Author(s):

William Miller ◽

Hua Chen ◽

Da-Lin Zhang

Keyword(s):

Latent Heat ◽

Inner Core ◽

Vertical Motion ◽

Heat Of Fusion ◽

Rapid Intensification ◽

Latent Heat Of Fusion ◽

Hurricane Wilma ◽

Convective Bursts ◽

Upper Level ◽

Reduced Rate

Abstract The impacts of the latent heat of fusion on the rapid intensification (RI) of Hurricane Wilma (2005) are examined by comparing a 72-h control simulation (CTL) of the storm to a sensitivity simulation in which the latent heat of deposition is reduced by removing fusion heating (NFUS). Results show that, while both storms undergo RI, the intensification rate is substantially reduced in NFUS. At peak intensity, NFUS is weaker than CTL by 30 hPa in minimum central pressure and by 12 m s−1 in maximum surface winds. The reduced rate of surface pressure falls in NFUS appears to result hydrostatically from less upper-level warming in the eye. It is shown that CTL generates more inner-core convective bursts (CBs) during RI, with higher altitudes of peak vertical motion in the eyewall, compared to NFUS. The latent heat of fusion contributes positively to sufficient eyewall conditional instability to support CB updrafts. Slantwise soundings taken in CB updraft cores reveal moist adiabatic lapse rates until 200 hPa, where the updraft intensity peaks. These results suggest that CBs may impact hurricane intensification by inducing compensating subsidence of the lower-stratospheric air, and the authors conclude that the development of more CBs inside the upper-level radius of maximum wind and at the higher altitude of latent heating all appear to be favorable for the RI of Wilma.

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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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Why does rapid contraction of the radius of maximum wind precede rapid intensification in tropical cyclones?

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-21-0129.1 ◽

2021 ◽

Author(s):

Yuanlong Li ◽

Yuqing Wang ◽

Yanluan Lin ◽

Xin Wang

Keyword(s):

Tropical Cyclones ◽

Radial Distribution ◽

Diabatic Heating ◽

Rate Of Change ◽

Rapid Intensification ◽

Absolute Vorticity ◽

Radial Gradient ◽

Maximum Wind ◽

Tangential Wind ◽

Vorticity Flux

AbstractThe radius of maximum wind (RMW) has been found to contract rapidly well preceding rapid intensification in tropical cyclones (TCs) in recent literature but the understanding of the involved dynamics is incomplete. In this study, this phenomenon is revisited based on ensemble axisymmetric numerical simulations. Consistent with previous studies, because the absolute angular momentum (AAM) is not conserved following the RMW, the phenomenon can not be understood based on the AAM-based dynamics. Both budgets of tangential wind and the rate of change in the RMW are shown to provide dynamical insights into the simulated relationship between the rapid intensification and rapid RMW contraction. During the rapid RMW contraction stage, due to the weak TC intensity and large RMW, the moderate negative radial gradient of radial vorticity flux and small curvature of the radial distribution of tangential wind near the RMW favor rapid RMW contraction but weak diabatic heating far inside the RMW leads to weak low-level inflow and small radial absolute vorticity flux near the RMW and thus a relatively small intensification rate. As RMW contraction continues and TC intensity increases, diabatic heating inside the RMW and radial inflow near the RMW increase, leading to a substantial increase in radial absolute vorticity flux near the RMW and thus the rapid TC intensification. However, the RMW contraction rate decreases rapidly due to the rapid increase in the curvature of the radial distribution of tangential wind near the RMW as the TC intensifies rapidly and RMW decreases.

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Vertical Vortex Development in Hurricane Michael (2018) during Rapid Intensification

Monthly Weather Review ◽

10.1175/mwr-d-21-0098.1 ◽

2021 ◽

Author(s):

Alexander J. DesRosiers ◽

Michael M. Bell ◽

Ting-Yu Cha

Keyword(s):

Inner Core ◽

Doppler Radar ◽

Three Dimensional ◽

Vertical Gradient ◽

Machine Learning Techniques ◽

Rapid Intensification ◽

Wind Retrieval ◽

Retrieval Technique ◽

Budget Analysis ◽

Tangential Wind

AbstractThe landfall of Hurricane Michael (2018) at category 5 intensity occurred after rapid intensification (RI) spanning much of the storm’s lifetime. Four Hurricane Hunter aircraft missions observed the RI period with tail Doppler radar (TDR). Data from each of the 14 aircraft passes through the storm were quality controlled via a combination of interactive and machine learning techniques. TDR data from each pass were synthesized using the SAMURAI variational wind retrieval technique to yield three-dimensional kinematic fields of the storm to examine inner core processes during RI. Vorticity and angular momentum increased and concentrated in the eyewall region. A vorticity budget analysis indicates the tendencies became more axisymmetric over time. In this study we focus in particular on how the eyewall vorticity tower builds vertically into the upper levels. Horizontal vorticity associated with the vertical gradient of tangential wind was tilted into the vertical by the eyewall updraft to yield a positive vertical vorticity tendency inward atop the existing vorticity tower, that is further developed locally upward and outward along the sloped eyewall through advection and stretching. Observed maintenance of thermal wind balance from a thermodynamic retrieval shows evidence of a strengthening warm core, which aided in lowering surface pressure and further contributed to the efficient intensification in the latter stages of this RI event.

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NASA’s Hurricane and Severe Storm Sentinel (HS3) Investigation

Bulletin of the American Meteorological Society ◽

10.1175/bams-d-15-00186.1 ◽

2016 ◽

Vol 97 (11) ◽

pp. 2085-2102 ◽

Cited By ~ 34

Author(s):

Scott A. Braun ◽

Paul A. Newman ◽

Gerald M. Heymsfield

Keyword(s):

East Coast ◽

Inner Core ◽

The United States ◽

Intensity Change ◽

Western Coast ◽

Rapid Intensification ◽

Physical Processes ◽

Severe Storm ◽

Saharan Air Layer ◽

Global Hawk

Abstract The National Aeronautics and Space Administration’s (NASA) Hurricane and Severe Storm Sentinel (HS3) investigation was a multiyear field campaign designed to improve understanding of the physical processes that control hurricane formation and intensity change, specifically the relative roles of environmental and inner-core processes. Funded as part of NASA’s Earth Venture program, HS3 conducted 5-week campaigns during the hurricane seasons of 2012–14 using the NASA Global Hawk aircraft, along with a second Global Hawk in 2013 and a WB-57f aircraft in 2014. Flying from a base at Wallops Island, Virginia, the Global Hawk could be on station over storms for up to 18 h off the East Coast of the United States and up to about 6 h off the western coast of Africa. Over the 3 years, HS3 flew 21 missions over nine named storms, along with flights over two nondeveloping systems and several Saharan air layer (SAL) outbreaks. This article summarizes the HS3 experiment, the missions flown, and some preliminary findings related to the rapid intensification and outflow structure of Hurricane Edouard (2014) and the interaction of Hurricane Nadine (2012) with the SAL.

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Evaluation of a Wind-Wave System for Ensemble Tropical Cyclone Wave Forecasting. Part I: Winds

Weather and Forecasting ◽

10.1175/waf-d-12-00054.1 ◽

2013 ◽

Vol 28 (2) ◽

pp. 297-315 ◽

Cited By ~ 4

Author(s):

Steven M. Lazarus ◽

Samuel T. Wilson ◽

Michael E. Splitt ◽

Gary A. Zarillo

Keyword(s):

Tropical Cyclone ◽

Inner Core ◽

Synthetic Data ◽

Radial Distance ◽

Wave System ◽

Computationally Efficient ◽

Wind Fields ◽

Translation Speed ◽

Maximum Wind ◽

Regional Reanalysis

Abstract A computationally efficient method of producing tropical cyclone (TC) wind analyses is developed and tested, using a hindcast methodology, for 12 Gulf of Mexico storms. The analyses are created by blending synthetic data, generated from a simple parametric model constructed using extended best-track data and climatology, with a first-guess field obtained from the NCEP–NCAR North American Regional Reanalysis (NARR). Tests are performed whereby parameters in the wind analysis and vortex model are varied in an attempt to best represent the TC wind fields. A comparison between nonlinear and climatological estimates of the TC size parameter indicates that the former yields a much improved correlation with the best-track radius of maximum wind rm. The analysis, augmented by a pseudoerror term that controls the degree of blending between the NARR and parametric winds, is tuned using buoy observations to calculate wind speed root-mean-square deviation (RMSD), scatter index (SI), and bias. The bias is minimized when the parametric winds are confined to the inner-core region. Analysis wind statistics are stratified within a storm-relative reference frame and by radial distance from storm center, storm intensity, radius of maximum wind, and storm translation speed. The analysis decreases the bias and RMSD in all quadrants for both moderate and strong storms and is most improved for storms with an rm of less than 20 n mi. The largest SI reductions occur for strong storms and storms with an rm of less than 20 n mi. The NARR impacts the analysis bias: when the bias in the former is relatively large, it remains so in the latter.

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