Abstract Midlevel ventilation, or the flux of low-entropy air into inner core a tropical cyclone (TC), is hypothesized mechanism by which environmental vertical wind shear can constrain cyclone’s intensity. An idealized framework based on steadiness, axisymmetry, and slantwise neutrality developed to assess how ventilation affects intensity via two possible pathways: first through downdrafts outside eyewall second eddy fluxes directly eyewall. For both pathways, has detrimental effect...

An important environmental control of both tropical cyclone intensity and genesis is vertical wind shear. One hypothesized pathway by which shear affects cyclones midlevel ventilation—or the flux low-entropy air into center cyclone. Based on a theoretical framework, ventilation index introduced that equal to multiplied nondimensional entropy deficit divided potential intensity. The has strong influence climatology. Tropical cyclogenesis preferentially occurs when where anomalously low. Both...

Abstract Understanding trends in large hail-producing environments is an important component of estimating hail risk. Here, we use two environmental parameters, the Large Hail Parameter and Significant Parameter, to assess days with conducive for ≥5 cm. From 1979 2017, there has been increase favorable central eastern portions U.S. This driven primarily by increasing frequency steep mid-tropospheric lapse rates necessary combinations instability vertical wind shear severe thunderstorms....

A new pathway for the negative impact of ENSO on tropical North Atlantic (NAtl) storm activity is examined empirically. Anomalous tropospheric temperatures communicated from Pacific by wave dynamics are hypothesized to development affecting column stability relative equilibrium with NAtl sea surface temperature (SST). This combines recent teleconnection theory role temperature‐SST differences in hurricane intensity theory. An principle component (EQ PC) which SST and covary, explains most...

Abstract The sensitivity of tropical cyclone intensity to ventilation cooler, drier air into the inner core is examined using an axisymmetric model with parameterized ventilation. Sufficiently strong induces cooling upper-level warm core, a shift in secondary circulation radially outward, and decrease simulated intensity. Increasing strength placing at middle lower levels results greater quasi-steady intensity, whereas has little effect on For ventilation, oscillatory regime materializes...

This review article summarizes recent (2014–2019) advances in our understanding of tropical cyclogenesis, stemming from activities at the ninth International Workshop on Tropical Cyclones. cyclogenesis involves interaction dynamic and thermodynamic processes multiple spatio-temporal scales. Studies have furthered how may be affected by external processes, such as intraseasonal oscillations, monsoon circulations, intertropical convergence zone, midlatitude troughs cutoff lows. Additionally,...

Abstract The ventilation index serves as a theoretically based metric to assess possible changes in the statistics of tropical cyclones combined vertical wind shear, midlevel entropy deficit, and potential intensity climate models. Model output from eight Coupled Intercomparison Project 5 models is used calculate index. its relationship cyclone activity between two 20 year periods are compared: historical experiment 1981 2000 RCP8.5 2081 2100. general tendency for an increase seasonal...

The relationship between tropical cyclone (TC) convective characteristics and TC intensity change is explored using infrared passive microwave satellite imagery of TCs in the North Atlantic eastern Pacific basins from 1989 to 2016. episodes were placed into one four groups: rapid intensification (RI), slow (SI), neutral (N), weakening (W). To account for differences distributions among groups, a normalization technique introduced, which allows analysis anomalous their change. A composite...

Abstract The role of upper-tropospheric troughs on the intensification rate newly formed tropical cyclones (TCs) is analyzed. This study focuses TCs forming in presence North Atlantic basin between 1980 and 2014. were binned into three groups based upon 24-h starting at time genesis: rapid TC genesis (RTCG), slow (STCG), neutral (NTCG). Composite analysis shows RTCG events are characterized by amplified flow with largest upshear displacement trough groups. associated greater quasigeostrophic...

Abstract This study demonstrates how midlevel dry air and vertical wind shear (VWS) can modulate tropical cyclone (TC) development via radial ventilation. A suite of experiments was conducted with different combinations initial moisture VWS environments. Two ventilation structures are documented. The first structure is positioned in a similar region as rainband activity downdraft (documented Part I) between heights 0 3 km. Parcels associated this transport low–equivalent potential...

Abstract An updated climatology of Atlantic basin tropical cyclone (TC) intensity change in the presence upper tropospheric trough forcing is presented. To control for changes background thermodynamic environment, a methodology that normalizes by potential TC used to more narrowly focus on effect troughs compared previous studies. Relative full sample TCs, are negative influence intensification: interaction cases 4% less likely intensify and 5% weaken. Troughs especially detrimental TCs...

Abstract Tropical cyclone (TC)–trough interactions are a common occurrence in the North Atlantic basin and lead to variety of TC intensity changes, from rapid intensification (RI) weakening. To test whether certain TC–trough configurations more favorable for RI than others, upper-tropospheric troughs involved such were objectively classified into one three clusters through implementation machine-learning, dimensionality-reduction technique conjunction with k -means clustering algorithm....

Abstract This study examines how midlevel dry air and vertical wind shear (VWS) can modulate tropical cyclone (TC) development via downdraft ventilation. A suite of experiments was conducted with different combinations initial moisture VWS. strong, positive, linear relationship exists between the low-level mass flux in inner core TC intensity. The increase intensity is not due to an increased strength upward motions but, instead, areal extent strong ( w > 0.5 m s −1 ). suggests physical...

Abstract The 22 May 2014 Duanesburg, New York, supercell produced an enhanced Fujita scale category 3 (EF3) tornado and 10-cm-diameter hail. synoptic setup for the event was ambiguous compared to other documented cases of Northeast tornadoes. Mesoscale inhomogeneities due terrain baroclinic boundaries played a key role in evolution severity storm. storm initiated at intersection outflow boundary north–south-oriented boundary. mesocyclone able sustain itself as result sufficiently large...

Abstract To better understand the conditions that favor tropical cyclone (TC) rapid intensification (RI), this study assesses environmental and storm-scale characteristics differentiate TCs undergo RI from slow (SI). This comparison is performed between analog TC pairs have similar initial intensity, vertical wind shear, maximum potential intensity. Differences in of SI North Atlantic western Pacific basins are evaluated by compositing comparing data fifth-generation European Centre for...

Abstract Idealized experiments conducted with an axisymmetric tropical cyclone (TC) model are used to assess the effects of midlevel dry air on TC secondary circulation. Moist entropy diagnostics convective parcels determine how affects distribution and strength convection. Analyzing upward downward motions in Eulerian radius–height coordinate system shows that moistest simulation has stronger vertical a wider overturning circulation compared drier simulations. A Lagrangian framework further...

Abstract The sensitivity of tropical cyclone spinup time to the initial entropy deficit troposphere is examined in an axisymmetric hurricane model. Larger deficits correspond less moisture above lifting condensation level a subcloud-layer parcel. quantified terms thresholds integrated horizontal kinetic energy within radius 300 km and below height 1.5 km. increases sublinearly with increasing deficit, indicating greatest lies profiles closer saturation. As profile approaches saturation,...

The Pre-Depression Investigation of Cloud-systems in the Tropics (PREDICT) field experiment successfully gathered data from four developing and decaying/nondeveloping tropical disturbances over North Atlantic basin between 15 August 30 September 2010. invaluable roles played by early career scientists (ECSs) throughout campaign helped make possible successful execution program's mission to investigate cyclone formation. ECSs provided critical meteorological information— often obtained novel...

Abstract One source of uncertainty associated with vertical wind shear (VWS) on tropical cyclone (TC) intensity evolution arises when the VWS becomes sufficiently strong such that TC vortex is unable to overcome inhibiting effects (the critical regime), resulting in a transition from realignment and eventual reintensification persistent misalignment failure reintensification. To uncover initiation mechanism behavioral transition, this study examines dynamical tilt precession through set CM1...

Abstract Quantifying and reducing the uncertainty of model parameterizations using observations is evaluated for tropical cyclone (TC) intensity prediction. This accomplished a nonlinear inverse modeling technique that produces joint probability density function (PDF) set parameters. The dependence estimated parameter values associated on two types observable quantities analyzed an axisymmetric hurricane model. When observation only maximum tangential wind speed, PDF estimates has large...

Abstract An ensemble of axisymmetric model experiments with simplified physics is used to evaluate the diagnostic framework presented in Part I. The central piece understanding what causes decreases ratio bulk differences moist entropy over angular momentum between two defined regions, boundary demarcating approximate location emergence radius maximum wind developing meso-beta-scale protovortex. Within a day before tropical cyclogenesis, forcing results decrease this ratio. Net advective...

Abstract A diagnostic framework to investigate the role of processes around and during tropical cyclogenesis is presented. The key metric ratio bulk differences moist entropy over angular momentum between an inner outer region a disturbance or cyclone. This hypothesized decrease become negative as both high-entropy core low-level vortex in amplify cyclogenesis. time tendency this can be split into two forcings: forcing forcing. Each further divided components comprising net advective fluxes...

Abstract A statistical downscaling algorithm is introduced to forecast surface wind speed at a location. The consists of resolved and unresolved components yield time series synthetic speeds high resolution. component bias-corrected numerical weather prediction model the 10-m simulated high-frequency that trained match variance power spectral density observations Because stochastic nature speed, may be repeated an ensemble speeds. used generate probabilistic predictions sustained or gusts....