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Abstract
Results from this multihurricane study suggest that the criticality of the oft-cited 26°C hurricane threshold linked to hurricane maintenance may be more closely associated with atmospheric thermodynamic conditions within the inner core than previously believed. In all cases, a positive sea–air contrast was observed within the storm inner core (i.e., surface ocean temperature greater than surface air temperature), despite the fact that 6% of the hurricanes exhibited sea surface temperatures (SSTs) less than the 26°C. For the storms sampled in this study, inner-core surface dewpoint temperatures never exceeded 26.5°C. This finding may provide an alternate explanation as to the criticality of the 26°C threshold since SSTs above 26°C would, in almost all instances, be associated with a positive enthalpy flux condition. Analyses from this study also illustrate that high wind SSTs fluctuate as a function of storm latitude, while inner-core near-surface dewpoint temperatures are much less sensitive to this parameter. As a result, and assuming all other factors to be equal, low-latitude hurricanes would, on average, be expected to experience surface moisture fluxes ~1/3 greater than storms located farther to the north. For systems sampled within the deep tropics, inner-core SST was found to fluctuate much less than surface dewpoint temperature, suggesting that the atmosphere, not the ocean, is more likely to influence the key thermodynamic parameter controlling surface moisture flux for this subset of hurricanes.
Abstract
Results from this multihurricane study suggest that the criticality of the oft-cited 26°C hurricane threshold linked to hurricane maintenance may be more closely associated with atmospheric thermodynamic conditions within the inner core than previously believed. In all cases, a positive sea–air contrast was observed within the storm inner core (i.e., surface ocean temperature greater than surface air temperature), despite the fact that 6% of the hurricanes exhibited sea surface temperatures (SSTs) less than the 26°C. For the storms sampled in this study, inner-core surface dewpoint temperatures never exceeded 26.5°C. This finding may provide an alternate explanation as to the criticality of the 26°C threshold since SSTs above 26°C would, in almost all instances, be associated with a positive enthalpy flux condition. Analyses from this study also illustrate that high wind SSTs fluctuate as a function of storm latitude, while inner-core near-surface dewpoint temperatures are much less sensitive to this parameter. As a result, and assuming all other factors to be equal, low-latitude hurricanes would, on average, be expected to experience surface moisture fluxes ~1/3 greater than storms located farther to the north. For systems sampled within the deep tropics, inner-core SST was found to fluctuate much less than surface dewpoint temperature, suggesting that the atmosphere, not the ocean, is more likely to influence the key thermodynamic parameter controlling surface moisture flux for this subset of hurricanes.
Abstract
Scientists at NOAA's Hurricane Research Division recently analyzed the inner-core upper-ocean environment for 23 Atlantic, Gulf of Mexico, and Caribbean hurricanes between 1975 and 2002. The interstorm variability of sea surface temperature (SST) change between the hurricane inner-core environment and the ambient ocean environment ahead of the storm is documented using airborne expendable bathythermograph (AXBT) observations and buoy-derived archived SST data. The authors demonstrate that differences between inner-core and ambient SST are much less than poststorm, “cold wake” SST reductions typically observed (i.e., ∼0°–2°C versus 4°–5°C). These findings help define a realistic parameter space for storm-induced SST change within the important high-wind inner-core hurricane environment. Results from a recent observational study yielded estimates of upper-ocean heat content, upper-ocean energy extracted by the storm, and upper-ocean energy utilization for a wide range of tropical systems. Results from this analysis show that, under most circumstances, the energy available to the tropical cyclone is at least an order of magnitude greater than the energy extracted by the storm. This study also highlights the significant impact that changes in inner-core SST have on the magnitude of air–sea fluxes under high-wind conditions. Results from this study illustrate that relatively modest changes in inner-core SST (order 1°C) can effectively alter maximum total enthalpy (sensible plus latent heat) flux by 40% or more.
The magnitude of SST change (ambient minus inner core) was statistically linked to subsequent changes in storm intensity for the 23 hurricanes included in this research. These findings suggest a relationship between reduced inner-core SST cooling (i.e., increased inner-core surface enthalpy flux) and tropical cyclone intensification. Similar results were not found when changes in storm intensity were compared with ambient SST or upper-ocean heat content conditions ahead of the storm. Under certain circumstances, the variability associated with inner-core SST change appears to be an important factor directly linked to the intensity change process.
Abstract
Scientists at NOAA's Hurricane Research Division recently analyzed the inner-core upper-ocean environment for 23 Atlantic, Gulf of Mexico, and Caribbean hurricanes between 1975 and 2002. The interstorm variability of sea surface temperature (SST) change between the hurricane inner-core environment and the ambient ocean environment ahead of the storm is documented using airborne expendable bathythermograph (AXBT) observations and buoy-derived archived SST data. The authors demonstrate that differences between inner-core and ambient SST are much less than poststorm, “cold wake” SST reductions typically observed (i.e., ∼0°–2°C versus 4°–5°C). These findings help define a realistic parameter space for storm-induced SST change within the important high-wind inner-core hurricane environment. Results from a recent observational study yielded estimates of upper-ocean heat content, upper-ocean energy extracted by the storm, and upper-ocean energy utilization for a wide range of tropical systems. Results from this analysis show that, under most circumstances, the energy available to the tropical cyclone is at least an order of magnitude greater than the energy extracted by the storm. This study also highlights the significant impact that changes in inner-core SST have on the magnitude of air–sea fluxes under high-wind conditions. Results from this study illustrate that relatively modest changes in inner-core SST (order 1°C) can effectively alter maximum total enthalpy (sensible plus latent heat) flux by 40% or more.
The magnitude of SST change (ambient minus inner core) was statistically linked to subsequent changes in storm intensity for the 23 hurricanes included in this research. These findings suggest a relationship between reduced inner-core SST cooling (i.e., increased inner-core surface enthalpy flux) and tropical cyclone intensification. Similar results were not found when changes in storm intensity were compared with ambient SST or upper-ocean heat content conditions ahead of the storm. Under certain circumstances, the variability associated with inner-core SST change appears to be an important factor directly linked to the intensity change process.
Abstract
Midlatitude cyclones develop off the Carolinas during winters and move north producing gale-force winds, ice, and heavy snow. It is believed that boundary-layer and air-sea interaction processes are very important during the development stages of these East Coast storms. The marine boundary layer (MBL) off the mid- Atlantic coastline is highly baroclinic due to the proximity of the Gulf Stream just offshore.
Typical horizontal distances between the Wilmington coastline and the western edge of the Gulf Stream vary between 90 and 250 km annually, and this distance can deviate by over 30 km within a single week. While similar weekly Gulf Stream position standard deviations also exist at Cape Hatteras, the average annual distance to the Gulf Stream frontal zone is much smaller off Cape Hatteras, normally ranging between 30 and 100 km.
This research investigates the low-level baroclinic conditions present prior to observed storm events. The examination of nine years of data on the Gulf Stream position and East Coast winter storms seems to indicate that the degree of low-level baroclinicity and modification existing prior to a cyclonic event may significantly affect the rate of cyclonic deepening off the mid-Atlantic coastline. Statistical analyses linking the observed surface-pressure decrease with both the Gulf Stream frontal location and the prestorm coastal baroclinic conditions are presented. These results quantitatively indicate that Gulf Stream-induced wintertime baroclinicity may significantly affect the regional intensification of East Coast winter cyclones.
Abstract
Midlatitude cyclones develop off the Carolinas during winters and move north producing gale-force winds, ice, and heavy snow. It is believed that boundary-layer and air-sea interaction processes are very important during the development stages of these East Coast storms. The marine boundary layer (MBL) off the mid- Atlantic coastline is highly baroclinic due to the proximity of the Gulf Stream just offshore.
Typical horizontal distances between the Wilmington coastline and the western edge of the Gulf Stream vary between 90 and 250 km annually, and this distance can deviate by over 30 km within a single week. While similar weekly Gulf Stream position standard deviations also exist at Cape Hatteras, the average annual distance to the Gulf Stream frontal zone is much smaller off Cape Hatteras, normally ranging between 30 and 100 km.
This research investigates the low-level baroclinic conditions present prior to observed storm events. The examination of nine years of data on the Gulf Stream position and East Coast winter storms seems to indicate that the degree of low-level baroclinicity and modification existing prior to a cyclonic event may significantly affect the rate of cyclonic deepening off the mid-Atlantic coastline. Statistical analyses linking the observed surface-pressure decrease with both the Gulf Stream frontal location and the prestorm coastal baroclinic conditions are presented. These results quantitatively indicate that Gulf Stream-induced wintertime baroclinicity may significantly affect the regional intensification of East Coast winter cyclones.
Abstract
Composite analyses of marine surface observations from 37 hurricanes between 1975 and 1998 show that the difference between the sea surface temperature and the surface air temperature significantly increases just outside the hurricane inner core. This increase in the sea–air contrast is primarily due to a reduction in surface air temperature and is more likely to occur when sea temperatures are at least 27°C. Results show that 90% of the observed cooling occurs 3.25°–1.25° latitude from the hurricane center, well outside the region of strongest surface winds. Since surface pressure only decreases 3 mb over this interval, the ∼2°C drop in air temperature is not a result of adiabatic expansion.
For the subset of observations that contained moisture measurements, surface specific humidity decreased 1.2 g kg−1 4.5°–1.75° latitude from the storm center. This finding suggests that the observed reduction in surface air temperature is not simply a result of near-surface evaporation from sea spray or precipitation. An alternate explanation may be that outside the hurricane inner core, unsaturated convective downdrafts act to dry and evaporatively cool the near-surface environment.
Between 3.25° and 1.25° radius, composite analyses show that low-level inflow is not isothermal, surface moisture is not constant, and the near-surface environment is not in thermodynamic equilibrium with the sea. Calculations based on these observations show that θ e decreases between 4.0° and 1.25° radius and then quickly rises near the inner core as surface pressures fall and specific humidity increases. Surface fluxes of heat and moisture are also observed to significantly increase near the inner core. The largest increase in surface sensible heat flux occurs radially inward of 1.5°, where surface winds are strong and sea–air temperature contrasts are greatest. As a result, the average Bowen ratio is 0.20∼0.5° radius from the composite storm center. This increase in sensible heat flux (in conjunction with near-saturated conditions at low to midlevels) may help explain why average surface air temperatures inside 1.25° radius remain relatively constant, despite the potential for additional cooling from evaporation and adiabatic expansion within the high wind inner core.
Abstract
Composite analyses of marine surface observations from 37 hurricanes between 1975 and 1998 show that the difference between the sea surface temperature and the surface air temperature significantly increases just outside the hurricane inner core. This increase in the sea–air contrast is primarily due to a reduction in surface air temperature and is more likely to occur when sea temperatures are at least 27°C. Results show that 90% of the observed cooling occurs 3.25°–1.25° latitude from the hurricane center, well outside the region of strongest surface winds. Since surface pressure only decreases 3 mb over this interval, the ∼2°C drop in air temperature is not a result of adiabatic expansion.
For the subset of observations that contained moisture measurements, surface specific humidity decreased 1.2 g kg−1 4.5°–1.75° latitude from the storm center. This finding suggests that the observed reduction in surface air temperature is not simply a result of near-surface evaporation from sea spray or precipitation. An alternate explanation may be that outside the hurricane inner core, unsaturated convective downdrafts act to dry and evaporatively cool the near-surface environment.
Between 3.25° and 1.25° radius, composite analyses show that low-level inflow is not isothermal, surface moisture is not constant, and the near-surface environment is not in thermodynamic equilibrium with the sea. Calculations based on these observations show that θ e decreases between 4.0° and 1.25° radius and then quickly rises near the inner core as surface pressures fall and specific humidity increases. Surface fluxes of heat and moisture are also observed to significantly increase near the inner core. The largest increase in surface sensible heat flux occurs radially inward of 1.5°, where surface winds are strong and sea–air temperature contrasts are greatest. As a result, the average Bowen ratio is 0.20∼0.5° radius from the composite storm center. This increase in sensible heat flux (in conjunction with near-saturated conditions at low to midlevels) may help explain why average surface air temperatures inside 1.25° radius remain relatively constant, despite the potential for additional cooling from evaporation and adiabatic expansion within the high wind inner core.
Abstract
The relationship between deep-layer environmental wind shear direction and tropical cyclone (TC) boundary layer thermodynamic structures is explored in multiple independent databases. Analyses derived from the tropical cyclone buoy database (TCBD) show that when TCs experience northerly component shear, the 10-m equivalent potential temperature θe tends to be more symmetric than when shear has a southerly component. The primary asymmetry in θe in TCs experiencing southerly component shear is radially outward from 2 times the radius of maximum wind speed, with the left-of-shear quadrants having lower θe by 4–6 K than the right-of-shear quadrants. As with the TCBD, an asymmetric distribution of 10-m θe for TCs experiencing southerly component shear and a symmetric distribution of 10-m θe for TCs experiencing northerly component shear was found using composite observations from dropsondes. These analyses show that differences in the degree of symmetry near the sea surface extend through the depth of the boundary layer. Additionally, mean dropsonde profiles illustrate that TCs experiencing northerly component shear are more potentially unstable between 500- and 1000-m altitude, signaling a more favorable environment for the development of surface-based convection in rainband regions. Analyses from the Statistical Hurricane Intensity Prediction Scheme (SHIPS) database show that subsequent strengthening for TCs in the Atlantic Ocean basin preferentially occurs in northerly component deep-layer environmental wind shear environments whereas subsequent weakening preferentially occurs in southerly component wind shear environments, which further illustrates that the asymmetric distribution of boundary layer thermodynamics is unfavorable for TC intensification. These differences emphasize the impact of deep-layer wind shear direction on TC intensity changes that likely result from the superposition of large-scale advection with the shear-relative asymmetries in TC structure.
Significance Statement
This research investigates how the direction of the winds surrounding the storm impacts the strength of a tropical cyclone. Analyses from this study illustrate that when the winds come from the south the atmospheric boundary layer has a cool and dry side along with a warm and moist side. When the large-scale winds come from the north, temperature and moisture conditions are more uniform throughout the boundary layer. Consequently, results from tropical cyclone climatology show that winds observed to come from the north favor subsequent intensification. These relationships illustrate that tropical cyclone structure and intensity are directly influenced by their surrounding environments and that knowledge of the wind environment could help to improve future forecasts of tropical cyclone intensity change.
Abstract
The relationship between deep-layer environmental wind shear direction and tropical cyclone (TC) boundary layer thermodynamic structures is explored in multiple independent databases. Analyses derived from the tropical cyclone buoy database (TCBD) show that when TCs experience northerly component shear, the 10-m equivalent potential temperature θe tends to be more symmetric than when shear has a southerly component. The primary asymmetry in θe in TCs experiencing southerly component shear is radially outward from 2 times the radius of maximum wind speed, with the left-of-shear quadrants having lower θe by 4–6 K than the right-of-shear quadrants. As with the TCBD, an asymmetric distribution of 10-m θe for TCs experiencing southerly component shear and a symmetric distribution of 10-m θe for TCs experiencing northerly component shear was found using composite observations from dropsondes. These analyses show that differences in the degree of symmetry near the sea surface extend through the depth of the boundary layer. Additionally, mean dropsonde profiles illustrate that TCs experiencing northerly component shear are more potentially unstable between 500- and 1000-m altitude, signaling a more favorable environment for the development of surface-based convection in rainband regions. Analyses from the Statistical Hurricane Intensity Prediction Scheme (SHIPS) database show that subsequent strengthening for TCs in the Atlantic Ocean basin preferentially occurs in northerly component deep-layer environmental wind shear environments whereas subsequent weakening preferentially occurs in southerly component wind shear environments, which further illustrates that the asymmetric distribution of boundary layer thermodynamics is unfavorable for TC intensification. These differences emphasize the impact of deep-layer wind shear direction on TC intensity changes that likely result from the superposition of large-scale advection with the shear-relative asymmetries in TC structure.
Significance Statement
This research investigates how the direction of the winds surrounding the storm impacts the strength of a tropical cyclone. Analyses from this study illustrate that when the winds come from the south the atmospheric boundary layer has a cool and dry side along with a warm and moist side. When the large-scale winds come from the north, temperature and moisture conditions are more uniform throughout the boundary layer. Consequently, results from tropical cyclone climatology show that winds observed to come from the north favor subsequent intensification. These relationships illustrate that tropical cyclone structure and intensity are directly influenced by their surrounding environments and that knowledge of the wind environment could help to improve future forecasts of tropical cyclone intensity change.
Abstract
A unique dataset obtained from the Coyote small uncrewed aircraft system (sUAS) in the inner-core boundary layer of Hurricane Maria (2017) is assimilated using NOAA’s Hurricane Ensemble Data Assimilation System (HEDAS) for data assimilation and Hurricane Weather Research and Forecasting (HWRF) system for model advances. The case of study is 1800 UTC 23 September 2017 when Maria was a category-3 hurricane. In addition to the Coyote observations, measurements collected by the NOAA Lockheed WP-3D Orion and U.S. Air Force C-130 aircraft were also included. To support the assimilation of this unique dataset, a new online quality control (QC) technique in HEDAS scales the observation–background difference by the total uncertainty during data assimilation and uses the interquartile range outlier method to identify outlier observations. Experimental setup includes various very frequent cycling scenarios for a control that does not assimilate Coyote observations, assimilation of Coyote observations in addition to the control observations, and the application of online QC. Findings suggest progressively improved analyses with more-frequent cycling, Coyote assimilation, and application of online QC. This applies to verification statistics computed at the locations of both Coyote and non-Coyote observations. In terms of the storm structure, only experiments that assimilated the Coyote observations were able to reproduce the double-eyewall structure that was observed at the time of the analysis, which is more consistent with the intensity of the storm according to the observations that were collected. Limitations of the study and future plans are also discussed.
Significance Statement
Findings from this study illustrate the significant impact difficult-to-obtain, near-surface observations can have on improving the accuracy of tropical cyclone structure and intensity. Adding these novel measurements in a way that also includes advanced cycling and quality control techniques in data assimilation has the potential to improve public forecasts that are reliant upon detailed depictions of storm strength and boundary layer structure prior to landfall. The results speak to the importance of parallel and consistent advancements in modeling, data assimilation, and observational capabilities to improve the depiction of the tropical cyclone inner-core structure in numerical models.
Abstract
A unique dataset obtained from the Coyote small uncrewed aircraft system (sUAS) in the inner-core boundary layer of Hurricane Maria (2017) is assimilated using NOAA’s Hurricane Ensemble Data Assimilation System (HEDAS) for data assimilation and Hurricane Weather Research and Forecasting (HWRF) system for model advances. The case of study is 1800 UTC 23 September 2017 when Maria was a category-3 hurricane. In addition to the Coyote observations, measurements collected by the NOAA Lockheed WP-3D Orion and U.S. Air Force C-130 aircraft were also included. To support the assimilation of this unique dataset, a new online quality control (QC) technique in HEDAS scales the observation–background difference by the total uncertainty during data assimilation and uses the interquartile range outlier method to identify outlier observations. Experimental setup includes various very frequent cycling scenarios for a control that does not assimilate Coyote observations, assimilation of Coyote observations in addition to the control observations, and the application of online QC. Findings suggest progressively improved analyses with more-frequent cycling, Coyote assimilation, and application of online QC. This applies to verification statistics computed at the locations of both Coyote and non-Coyote observations. In terms of the storm structure, only experiments that assimilated the Coyote observations were able to reproduce the double-eyewall structure that was observed at the time of the analysis, which is more consistent with the intensity of the storm according to the observations that were collected. Limitations of the study and future plans are also discussed.
Significance Statement
Findings from this study illustrate the significant impact difficult-to-obtain, near-surface observations can have on improving the accuracy of tropical cyclone structure and intensity. Adding these novel measurements in a way that also includes advanced cycling and quality control techniques in data assimilation has the potential to improve public forecasts that are reliant upon detailed depictions of storm strength and boundary layer structure prior to landfall. The results speak to the importance of parallel and consistent advancements in modeling, data assimilation, and observational capabilities to improve the depiction of the tropical cyclone inner-core structure in numerical models.
Abstract
Airborne Doppler radar reflectivity data collected in hurricanes on the NOAA P-3 aircraft between 1997 and 2021 were parsed into different modes of precipitation: stratiform precipitation, shallow convection, moderate convection, and deep convection. Stratiform precipitation was the most frequent precipitation mode with 82.6% of all observed precipitation while deep convection was the most infrequent at 1.3%. When stratified by 12-h intensity change, intensifying TCs had a greater areal coverage of total convection in the eyewall compared to weakening and steady-state TCs. The largest difference in the azimuthal distributions in the precipitation modes was in deep convection, which was mostly confined to the downshear-left quadrant in weakening and steady-state hurricanes and more symmetrically distributed in intensifying hurricanes. For all intensity change categories, the most symmetrically distributed precipitation mode was stratiform rain. To build upon the results of a recent thermodynamic study, the precipitation data were recategorized for hurricanes experiencing deep-layer wind shear with either a northerly component or southerly component. Like intensifying storms, hurricanes that experienced northerly component shear had a more symmetric distribution of deep convection than southerly component shear storms, which had a distribution of deep convection that resembled weakening storms. The greatest difference in the precipitation distributions between the shear direction groups were in major hurricanes experiencing moderate (4.5–11 m s−1) wind shear values. Consistent with previous airborne radar studies, the results suggest that considering the distribution of deep convection and the thermodynamic distributions associated with differing environmental wind shear direction could aid TC intensity forecasts.
Significance Statement
This research investigates how the distribution of different types of precipitation are related to tropical cyclone (TC) intensity change. Even though deep convection—the tallest clouds—is the least frequent type of precipitation, it has the strongest relationship to intensity change with uniform distributions around the eyewall associated with intensification. Less significant relationships were noticed for shallower clouds and stratiform (lighter) rain. The study also analyzed how change in direction of the large-scale winds with height (wind shear) influences intensity change. When wind shear is northerly, there is a more symmetric distribution of deep convection compared to when wind shear is southerly. These relationships illustrate how wind shear direction influences TC convective structure and, in turn, TC intensity change.
Abstract
Airborne Doppler radar reflectivity data collected in hurricanes on the NOAA P-3 aircraft between 1997 and 2021 were parsed into different modes of precipitation: stratiform precipitation, shallow convection, moderate convection, and deep convection. Stratiform precipitation was the most frequent precipitation mode with 82.6% of all observed precipitation while deep convection was the most infrequent at 1.3%. When stratified by 12-h intensity change, intensifying TCs had a greater areal coverage of total convection in the eyewall compared to weakening and steady-state TCs. The largest difference in the azimuthal distributions in the precipitation modes was in deep convection, which was mostly confined to the downshear-left quadrant in weakening and steady-state hurricanes and more symmetrically distributed in intensifying hurricanes. For all intensity change categories, the most symmetrically distributed precipitation mode was stratiform rain. To build upon the results of a recent thermodynamic study, the precipitation data were recategorized for hurricanes experiencing deep-layer wind shear with either a northerly component or southerly component. Like intensifying storms, hurricanes that experienced northerly component shear had a more symmetric distribution of deep convection than southerly component shear storms, which had a distribution of deep convection that resembled weakening storms. The greatest difference in the precipitation distributions between the shear direction groups were in major hurricanes experiencing moderate (4.5–11 m s−1) wind shear values. Consistent with previous airborne radar studies, the results suggest that considering the distribution of deep convection and the thermodynamic distributions associated with differing environmental wind shear direction could aid TC intensity forecasts.
Significance Statement
This research investigates how the distribution of different types of precipitation are related to tropical cyclone (TC) intensity change. Even though deep convection—the tallest clouds—is the least frequent type of precipitation, it has the strongest relationship to intensity change with uniform distributions around the eyewall associated with intensification. Less significant relationships were noticed for shallower clouds and stratiform (lighter) rain. The study also analyzed how change in direction of the large-scale winds with height (wind shear) influences intensity change. When wind shear is northerly, there is a more symmetric distribution of deep convection compared to when wind shear is southerly. These relationships illustrate how wind shear direction influences TC convective structure and, in turn, TC intensity change.
Abstract
Recent enhancements to the tropical cyclone-buoy database (TCBD) have incorporated data from the Extended Best Track (EBT) and the Statistical Hurricane Intensity Prediction Scheme (SHIPS) archive for tropical cyclones between 1975 and 2007. This information is used to analyze the relationships between large-scale atmospheric parameters, radial and shear-relative air–sea structure, and intensity change in strengthening and weakening hurricanes. Observations from this research illustrate that the direction of the large-scale vertical wind shear at mid- to low levels can impact atmospheric moisture conditions found near the surface. Drier low-level environments were associated with northerly shear conditions. In a separate analysis comparing strengthening and weakening hurricanes, drier surface conditions were also found for the intensifying sample. Since SST conditions were similar for both groups of storms, it is likely that the atmosphere was primarily responsible for modifying the near-surface thermodynamic environment (and ultimately surface moisture flux conditions) for this particular analysis.
Abstract
Recent enhancements to the tropical cyclone-buoy database (TCBD) have incorporated data from the Extended Best Track (EBT) and the Statistical Hurricane Intensity Prediction Scheme (SHIPS) archive for tropical cyclones between 1975 and 2007. This information is used to analyze the relationships between large-scale atmospheric parameters, radial and shear-relative air–sea structure, and intensity change in strengthening and weakening hurricanes. Observations from this research illustrate that the direction of the large-scale vertical wind shear at mid- to low levels can impact atmospheric moisture conditions found near the surface. Drier low-level environments were associated with northerly shear conditions. In a separate analysis comparing strengthening and weakening hurricanes, drier surface conditions were also found for the intensifying sample. Since SST conditions were similar for both groups of storms, it is likely that the atmosphere was primarily responsible for modifying the near-surface thermodynamic environment (and ultimately surface moisture flux conditions) for this particular analysis.
