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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
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
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
in the TCI dataset, as well as to examine the updrafts and downdrafts observed by the XDDs. Hock and Franklin (1999) used RD-93 dropsondes to derive vertical velocity from GPS fall speeds and a single drag force estimate presumed to be representative for all individual sondes. This method is now routine, but more recent studies use a hydrostatic pressure-derived fall speed rather than the GPS fall speed (e.g., Wang et al. 2015 ). Sonde-derived vertical velocities have been used to examine the
in the TCI dataset, as well as to examine the updrafts and downdrafts observed by the XDDs. Hock and Franklin (1999) used RD-93 dropsondes to derive vertical velocity from GPS fall speeds and a single drag force estimate presumed to be representative for all individual sondes. This method is now routine, but more recent studies use a hydrostatic pressure-derived fall speed rather than the GPS fall speed (e.g., Wang et al. 2015 ). Sonde-derived vertical velocities have been used to examine the
-level forcing mechanism), and this study identifies and quantifies a set of key common features for this class of TCs. The analyses in this study primarily rely on satellite observations, since these data typically provide the most complete spatial and temporal coverage over the storms, given that aircraft observations of TCs are rare in the eastern North Pacific (EPAC) and western Pacific (WPAC; Knabb et al. 2008 ). Without in situ reconnaissance data, intensity estimations and analyses are primarily
-level forcing mechanism), and this study identifies and quantifies a set of key common features for this class of TCs. The analyses in this study primarily rely on satellite observations, since these data typically provide the most complete spatial and temporal coverage over the storms, given that aircraft observations of TCs are rare in the eastern North Pacific (EPAC) and western Pacific (WPAC; Knabb et al. 2008 ). Without in situ reconnaissance data, intensity estimations and analyses are primarily
,c,e,f , 9b–f ). In addition, the “DA without VI” can cause large initial errors for MSW ( Figs. 8f , 9f ), indicating that the enhanced AMVs data only are not enough to force the storm intensity to match the observed intensity for this case. However, it is worth noting that the assimilation of enhanced AMVs in the inner-core region produces smaller average MSLP and MSW errors over the whole 72-h forecasts in most of the cases (e.g., the blue numbers at the top of each panel in Figs. 8b,c , 8e,f , and
,c,e,f , 9b–f ). In addition, the “DA without VI” can cause large initial errors for MSW ( Figs. 8f , 9f ), indicating that the enhanced AMVs data only are not enough to force the storm intensity to match the observed intensity for this case. However, it is worth noting that the assimilation of enhanced AMVs in the inner-core region produces smaller average MSLP and MSW errors over the whole 72-h forecasts in most of the cases (e.g., the blue numbers at the top of each panel in Figs. 8b,c , 8e,f , and
–pressure relationship of TC vortices approximately satisfies the gradient wind balance. In this subsection, we evaluate the impact of increasing resolution during DA on wind–pressure relationship in the analyzed vortices for an initial-hurricane case. The metric used is the net radial force field F as defined by Smith et al. (2009) , Pu et al. (2016) , and Lu and Wang (2019) . A closer-to-zero value of F indicates a better approximation to the gradient wind balance. Figure 10 shows the net radial force
–pressure relationship of TC vortices approximately satisfies the gradient wind balance. In this subsection, we evaluate the impact of increasing resolution during DA on wind–pressure relationship in the analyzed vortices for an initial-hurricane case. The metric used is the net radial force field F as defined by Smith et al. (2009) , Pu et al. (2016) , and Lu and Wang (2019) . A closer-to-zero value of F indicates a better approximation to the gradient wind balance. Figure 10 shows the net radial force
). This stable stratification is a necessary ingredient for adiabatic subsidence to warm the eye. Regardless of the forcing mechanisms, the strong upper-tropospheric warming between 22 and 23 October was enough to completely eliminate the TIL within the eye, allowing the tropopause height and temperature to increase dramatically. Fig . 10. Vertical cross sections of (a),(b) storm-relative radial and (c),(d) tangential velocity (m s −1 ) and the cold-point tropopause height (green lines) in Hurricane
). This stable stratification is a necessary ingredient for adiabatic subsidence to warm the eye. Regardless of the forcing mechanisms, the strong upper-tropospheric warming between 22 and 23 October was enough to completely eliminate the TIL within the eye, allowing the tropopause height and temperature to increase dramatically. Fig . 10. Vertical cross sections of (a),(b) storm-relative radial and (c),(d) tangential velocity (m s −1 ) and the cold-point tropopause height (green lines) in Hurricane
