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prior to Laura making landfall, compared with a synthetic aperture radar (SAR) pass at the same time ( Fig. 4 ). The methodology, strengths, and limitations of the SAR in estimating surface winds in intense hurricanes are described in Mouche et al. (2019) and Combot et al. (2020) . Laura was located on the western edge of the satellite swath, and only its eastern half was sampled. The SAR winds exceed 120 kt on the eastern side of the eyewall, with hurricane-force winds extending 85 km to the
prior to Laura making landfall, compared with a synthetic aperture radar (SAR) pass at the same time ( Fig. 4 ). The methodology, strengths, and limitations of the SAR in estimating surface winds in intense hurricanes are described in Mouche et al. (2019) and Combot et al. (2020) . Laura was located on the western edge of the satellite swath, and only its eastern half was sampled. The SAR winds exceed 120 kt on the eastern side of the eyewall, with hurricane-force winds extending 85 km to the
therein. Since ocean coupling and asymmetric forcing are present in nature, the intent of this paper is not to formally simulate Hurricane Patricia. Rather, the intent is to simulate a storm with a similar intensification rate and to examine the processes that produced the stability variations in the simulated storm. After an initial spinup period of about 20 h, the modeled storm ( Fig. 1 , blue lines) began an RI period that lasted approximately 18 h. After this RI, the storm continued to intensify
therein. Since ocean coupling and asymmetric forcing are present in nature, the intent of this paper is not to formally simulate Hurricane Patricia. Rather, the intent is to simulate a storm with a similar intensification rate and to examine the processes that produced the stability variations in the simulated storm. After an initial spinup period of about 20 h, the modeled storm ( Fig. 1 , blue lines) began an RI period that lasted approximately 18 h. After this RI, the storm continued to intensify
internally to CM1r18 was not used, in part for simplicity to remove any diurnal forcing and since the current domain, roughly 6000 km × 4000 km, is very large. In lieu of a diurnally varying radiation forcing, the simulations were carried out with Newtonian cooling capped at 2 K day −1 . To calculate the respective simulated brightness temperatures—both IR and WV—the CM1 output was passed to the Community Radiative Transfer Model (CRTM; Van Delst 2013 ; Grasso et al. 2008 ; Bikos et al. 2012 ; Jin et
internally to CM1r18 was not used, in part for simplicity to remove any diurnal forcing and since the current domain, roughly 6000 km × 4000 km, is very large. In lieu of a diurnally varying radiation forcing, the simulations were carried out with Newtonian cooling capped at 2 K day −1 . To calculate the respective simulated brightness temperatures—both IR and WV—the CM1 output was passed to the Community Radiative Transfer Model (CRTM; Van Delst 2013 ; Grasso et al. 2008 ; Bikos et al. 2012 ; Jin et
analysis of Patricia are presented in Part II. To further diagnose the differences among NoDA, VM, and DA, the gradient wind balance (GWB) relationship within each experiment is investigated. Following Smith et al. (2009) , a net radial force (NRF) field defined as the difference between the local radial pressure gradient force and the sum of centrifugal force and Coriolis force is used to describe the GWB relationship. This NRF is calculated on the pressure coordinates following Pu et al. (2009
analysis of Patricia are presented in Part II. To further diagnose the differences among NoDA, VM, and DA, the gradient wind balance (GWB) relationship within each experiment is investigated. Following Smith et al. (2009) , a net radial force (NRF) field defined as the difference between the local radial pressure gradient force and the sum of centrifugal force and Coriolis force is used to describe the GWB relationship. This NRF is calculated on the pressure coordinates following Pu et al. (2009
between large-scale forcing (e.g., rising branch of the Madden–Julian oscillation and deep convection coupled with a Central American gyre) and mesoscale processes including a localized gap wind event ( Kimberlain et al. 2016 ; Bosart et al. 2017 ). Patricia reached tropical storm intensity 18 h after becoming a tropical depression, eventually becoming a hurricane 24 h later, near 0000 UTC 22 October. At this time, Patricia was located in a very favorable environment with anomalously warm ocean
between large-scale forcing (e.g., rising branch of the Madden–Julian oscillation and deep convection coupled with a Central American gyre) and mesoscale processes including a localized gap wind event ( Kimberlain et al. 2016 ; Bosart et al. 2017 ). Patricia reached tropical storm intensity 18 h after becoming a tropical depression, eventually becoming a hurricane 24 h later, near 0000 UTC 22 October. At this time, Patricia was located in a very favorable environment with anomalously warm ocean
hypothesis, referred to as active outflow , is that a source of upper-level forcing that acts to accelerate or otherwise enhance the TC outflow can ultimately drive changes in the strength or structure of the vortex below (e.g., Sadler 1976 ; Holland and Merrill 1984 ; Nong and Emanuel 2003 ). Here, we do not seek to determine whether outflow is more likely to be passive or active. Instead, we explore the hypothesis that active outflow may contribute to TC intensification under the right set of
hypothesis, referred to as active outflow , is that a source of upper-level forcing that acts to accelerate or otherwise enhance the TC outflow can ultimately drive changes in the strength or structure of the vortex below (e.g., Sadler 1976 ; Holland and Merrill 1984 ; Nong and Emanuel 2003 ). Here, we do not seek to determine whether outflow is more likely to be passive or active. Instead, we explore the hypothesis that active outflow may contribute to TC intensification under the right set of
ventilating TCs, inducing a potential vorticity–related spinup, and outright shearing of the TC, depending on the proximity of the upper-level synoptic forcing. Vertical wind shear (VWS) is generally a negative influence on TC intensification ( Merrill 1988b ; Wang and Wu 2004 ). Recent studies on wind shear’s negative effects have focused on the thermodynamic effects of VWS, such as the midlevel ventilation ( Tang and Emanuel 2010 ; Tang and Emanuel 2012 ; Ge et al. 2013 ) or the flushing of the
ventilating TCs, inducing a potential vorticity–related spinup, and outright shearing of the TC, depending on the proximity of the upper-level synoptic forcing. Vertical wind shear (VWS) is generally a negative influence on TC intensification ( Merrill 1988b ; Wang and Wu 2004 ). Recent studies on wind shear’s negative effects have focused on the thermodynamic effects of VWS, such as the midlevel ventilation ( Tang and Emanuel 2010 ; Tang and Emanuel 2012 ; Ge et al. 2013 ) or the flushing of the
not contribute to stronger tangential winds at the surface, which may be due to the periodicity of the forcing and its concentrated location outside of the RMW. Heating anomalies in the current study extend a large horizontal distance in the upper troposphere, nearly 300 km long at later times in the extensive anvil of the Nightonly simulations (not shown). The expansive area of heating anomalies could contribute to a larger enhancement more similar to that reported by Navarro and Hakim (2016
not contribute to stronger tangential winds at the surface, which may be due to the periodicity of the forcing and its concentrated location outside of the RMW. Heating anomalies in the current study extend a large horizontal distance in the upper troposphere, nearly 300 km long at later times in the extensive anvil of the Nightonly simulations (not shown). The expansive area of heating anomalies could contribute to a larger enhancement more similar to that reported by Navarro and Hakim (2016
can lead to more skillful intensity forecasts. A common theoretical and numerical framework employed to understand TC intensification is predicated on the balanced vortex model ( Eliassen 1951 ), whereby an axisymmetric vortex is assumed to continuously evolve in a state of gradient wind and hydrostatic balance in response to a specified (often time invariant) forcing. Within the balanced vortex framework, it has been shown that heating concentrated radially inward of the radius of maximum
can lead to more skillful intensity forecasts. A common theoretical and numerical framework employed to understand TC intensification is predicated on the balanced vortex model ( Eliassen 1951 ), whereby an axisymmetric vortex is assumed to continuously evolve in a state of gradient wind and hydrostatic balance in response to a specified (often time invariant) forcing. Within the balanced vortex framework, it has been shown that heating concentrated radially inward of the radius of maximum
nonintensifying TCs have no such link ( Merrill 1988a ). Recent research has further demonstrated that outflow tends to develop in regions where upper-tropospheric inertial stability is low, and stronger outflow tends to be associated with intensifying TCs ( Rappin et al. 2011 ; Barrett et al. 2016 ; Komaromi and Doyle 2017 ). Synoptic-scale forcing has been found to further reduce upper-tropospheric inertial stability, which favors intensification ( Rappin et al. 2011 ). Additionally, eddy flux convergence
nonintensifying TCs have no such link ( Merrill 1988a ). Recent research has further demonstrated that outflow tends to develop in regions where upper-tropospheric inertial stability is low, and stronger outflow tends to be associated with intensifying TCs ( Rappin et al. 2011 ; Barrett et al. 2016 ; Komaromi and Doyle 2017 ). Synoptic-scale forcing has been found to further reduce upper-tropospheric inertial stability, which favors intensification ( Rappin et al. 2011 ). Additionally, eddy flux convergence
