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Evolution of the water vapor budget from the tropical wave stage to the tropical cyclone stage is examined using a high-resolution numerical model simulation. The focus is on a time window from 27 h prior to genesis to 9 h after genesis, and the diagnoses are carried out in the framework of the marsupial paradigm. Analysis shows that the vertically integrated inward moisture flux accounts for a majority of the total condensation and that its fractional contribution increases from the tropical wave stage to the tropical cyclone stage. The fractional contribution of the local evaporation is much smaller and decreases from the tropical wave stage to the tropical cyclone stage. It is also shown that the radial moisture flux above 850 hPa is rather weak prior to genesis but increases significantly after genesis because of the deepening of the inflow layer. The decrease in the fractional contribution of the local evaporation, or the increase in the fractional contribution of the vertically integrated inward moisture flux, is due to the strengthening of the low-level convergence associated with the secondary circulation. The intensification of the secondary circulation can be attributed to the organized convection and concentrated diabatic heating near the circulation center. The results suggest that the local evaporation and its positive interaction with the primary circulation may not be as important as generally appreciated for tropical cyclone development. By contrast, the increase in the fractional contribution by the inward moisture flux with the storm intensification implies the importance of the positive feedback among the primary circulation, the secondary circulation, and convection for tropical cyclone development.

The radius of maximum wind (RMW) defines the location of the maximum winds in a tropical cyclone and is critical to understanding intensity change as well as hazard impacts. A comparison between the Hurricane Analysis and Forecast System (HAFS) models and two statistical models based off the National Hurricane Center official forecast is conducted relative to a new baseline climatology to better understand whether models have skill in forecasting the RMW of North Atlantic tropical cyclones. On average, the HAFS models are less skillful than the climatology and persistence baseline and two statistically derived RMW estimates. The performance of the HAFS models is dependent on intensity with better skill for stronger tropical cyclones compared to weaker tropical cyclones. To further improve guidance of tropical cyclone hazards, more work needs to be done to improve forecasts of tropical cyclone structure. Plain Language Summary The radius of maximum wind (RMW) is a key structural parameter of tropical cyclones that describes how far the strongest winds are from the storm's center. The RMW is closely tied to significant hazards such as wind, storm surge, and rainfall. However, little forecast guidance is provided for the RMW resulting in forecasters using climatological estimates to help communicate hazard risk. In order to better forecast the RMW, we need to understand the performance of the few guidance techniques available. We compare RMW forecasts from the Hurricane Analysis and Forecast System (HAFS) to two statistical models and a climatological estimate. Forecasts of the RMW from HAFS are not competitive with statistical derivations of the RMW with marginally better to comparable skill for stronger tropical cyclones. The results indicate that there is a strong need for future improvements to better predict tropical cyclone structure in addition to track and intensity. Key Points Forecasting the radius of maximum wind (RMW) is important for forecasting tropical cyclone hazards A RMW climatology and persistence model is created to determine forecast skill Statistical RMW forecasts are skillful and outperform dynamical model guidance

The impacts of dry air on tropical cyclone formation are examined in the numerical model simulations of ex-Gaston (2010) and pre-Fay (2008). The former, a remnant low downgraded from a short-lived tropical cyclone, can be regarded as a nondeveloping system because it failed to redevelop, and the latter developed into a tropical cyclone despite lateral dry air entrainment and a transient upper-level dry air intrusion. Water vapor budget analysis suggests that the mean vertical moisture transport plays the dominant role in moistening the free atmosphere. Backward trajectory analysis and water budget analysis show that vertical transport of dry air from the middle and upper troposphere, where a well-defined wave pouch is absent, contributes to the midlevel drying near the pouch center in ex-Gaston. The midlevel drying suppresses deep convection, reduces moisture supply from the boundary layer, and contributes to the nondevelopment of ex-Gaston. Three-dimensional trajectory analysis based on the numerical model simulation of Fay suggests that dry air entrained at the pouch periphery tends to stay off the pouch center because of the weak midlevel inflow or gets moistened along its path even if it is being wrapped into the wave pouch. Lateral entrainment in the middle troposphere thus does not suppress convection near the pouch center or prevent the development of Tropical Storm Fay. This study suggests that the upper troposphere is a weak spot of the wave pouch at the early formation stage and that the vertical transport is likely a more direct pathway for dry air to influence moist convection near the pouch center.

The primary source of guidance used by the Storm Surge Unit (SSU) at the National Hurricane Center (NHC) for issuing storm surge watches and warnings is the Probabilistic Tropical Storm Surge model (P-Surge). P-Surge is an ensemble of Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model forecasts that is generated based on historical error distributions from NHC official forecasts. A probabilistic framework is used for operational storm surge forecasting to account for uncertainty related to the tropical cyclone track and wind forcing. Previous studies have shown that the size of a storm’s wind field is an important factor that can affect storm surge. A simple radius of maximum wind (RMW) prediction scheme was developed to forecast RMW based on NHC forecast parameters. Verification results indicate this scheme is an improvement over the RMW forecasts used by previous versions of P-Surge. To test the impact of the updated RMW forecasts in P-Surge, retrospective cases were selected from 25 storms from 2008 to 2020 that had an adequate number of observations. Evaluation of P-Surge forecasts using these improved RMW forecasts shows that the probability of detection is higher for most probability of exceedance thresholds. In addition, the forecast reliability is improved, and there is an increase in the number of high probability forecasts for extreme events at longer lead times. The improved RMW forecasts were recently incorporated into the operational version of P-Surge (v2.9), and serve as an important step toward extending the lead time of skillful and reliable storm surge forecasts.

In support of the National Science Foundation Pre-Depression Investigation of Cloud-systems in the tropics (NSF PREDICT) and National Aeronautics and Space Administration Genesis and Rapid Intensification Processes (NASA GRIP) dry run exercises and National Oceanic and Atmospheric Administration Hurricane Intensity Forecast Experiment (NOAA IFEX) during the 2009 hurricane season, a real-time wave-tracking algorithm and corresponding diagnostic analyses based on a recently proposed tropical cyclogenesis model were applied to tropical easterly waves over the Atlantic. The model emphasizes the importance of a Lagrangian recirculation region within a tropical-wave critical layer (the so-called pouch), where persistent deep convection and vorticity aggregation as well as column moistening are favored for tropical cyclogenesis. Distinct scenarios of hybrid wave–vortex evolution are highlighted. It was found that easterly waves without a pouch or with a shallow pouch did not develop. Although not all waves with a deep pouch developed into a tropical storm, a deep wave pouch had formed prior to genesis for all 16 named storms originating from monochromatic easterly waves during the 2008 and 2009 seasons. On the other hand, the diagnosis of two nondeveloping waves with a deep pouch suggests that strong vertical shear or dry air intrusion at the middle–upper levels (where a wave pouch was absent) can disrupt deep convection and suppress storm development. To sum up, this study suggests that a deep wave pouch extending from the midtroposphere (~600–700 hPa) down to the boundary layer is a necessary condition for tropical cyclone formation within an easterly wave. It is hypothesized also that a deep wave pouch together with other large-scale favorable conditions provides a sufficient condition for sustained convection and tropical cyclone formation. This hypothesized sufficient condition requires further testing and will be pursued in future work.

The Pre-Depression Investigation of Cloud-systems in the Tropics (PREDICT) field experiment successfully gathered data from four developing and four decaying/nondeveloping tropical disturbances over the tropical North Atlantic basin between 15 August and 30 September 2010. The invaluable roles played by early career scientists (ECSs) throughout the campaign helped make possible the successful execution of the field program's mission to investigate tropical cyclone formation. ECSs provided critical meteorological information—— often obtained from novel ECS-created products——during daily weather briefings that were used by the principal investigators in making mission planning decisions. Once a Gulfstream V (G-V) flight mission was underway, ECSs provided nowcasting support, relaying information that helped the mission scientists to steer clear of potential areas of turbulence aloft. Data from these missions, including dropsonde and GPS water vapor profiler data, were continually obtained, processed, and quality-controlled by ECSs. The dropsonde data provided National Hurricane Center forecasters and PREDICT mission scientists with real-time information regarding the characteristics of tropical disturbances. These data and others will serve as the basis for multiple ECS-led research topics over the years to come and are expected to provide new insights into the tropical cyclone formation process. PREDICT also provided invaluable educational and professional development experiences for ECSs, including the opportunity to critically evaluate observational evidence for tropical cyclone development theories and networking opportunities with their peers and established scientists in the field.

Recent concerns regarding herbicide spray drift, its subsequent effect on the surrounding environment, and herbicide efficacy have prompted applicators to focus on methods to reduce off-target movement of herbicides. Herbicide applications are complex processes, and as such, few studies have been conducted that consider multiple variables that affect the droplet spectrum of herbicide sprays. The objective of this study was to evaluate the effects of nozzle type, orifice size, herbicide active ingredient, pressure, and carrier volume on the droplet spectra of the herbicide spray. Droplet spectrum data were collected on 720 combinations of spray-application variables, which included six spray solutions (five herbicides and water alone), four carrier volumes, five nozzles, two orifice sizes, and three operating pressures. The laboratory study was conducted using a Sympatec laser diffraction instrument to determine the droplet spectrum characteristics of each treatment combination. When averaged over each main effect, nozzle type had the greatest effect on droplet size. Droplet size rankings for nozzles, ranked smallest to largest using volume median diameter (Dv0.5) values, were the XR, TT, AIXR, AI, and TTI nozzle with 176% change in Dv0.5 values from the XR to the TTI nozzle. On average, increasing the nozzle orifice size from a 11003 orifice to a 11005 increased the Dv0.5 values 8%. When compared with the water treatment, cloransulam (FirstRate) did not change the Dv0.5 value. Clethodim (Select Max), glyphosate (Roundup PowerMax), lactofen (Cobra), and glufosinate (Ignite) all reduced the Dv0.5 value 5, 11, 11, and 18%, respectively, when compared with water averaged over the other variables. Increasing the pressure of AIXR, TT, TTI, and XR nozzles from 138 to 276 kPa and the AI nozzle from 276 to 414 kPa decreased the Dv0.5 value 25%. Increasing the pressure from 276 to 414 kPa and from 414 to 552 kPa for the same nozzle group and AI nozzle decreased the Dv0.5 value 14%. Carrier volume had the least effect on the Dv0.5 value. Increasing the carrier volume from 47 to 187 L ha−1 increased the Dv0.5 value 5%, indicating that droplet size of the herbicides tested were not highly dependent on delivery volume. The effect on droplet size of the variables examined in this study from greatest effect to least effect were nozzle, operating pressure, herbicide, nozzle orifice size, and carrier volume. Nomenclature: Clethodim; cloransulam; glufosinate; glyphosate; lactofen. Recientemente ha habido preocupación por la deriva producto de la aplicación de herbicidas, su subsecuente efecto en el ambiente de los alrededores, y la eficacia del herbicida, lo que ha obligado a los aplicadores a enfocarse en métodos para reducir el movimiento de herbicidas a zonas fuera del objetivo deseado. Las aplicaciones de herbicidas son procesos complejos, y como tales, se han realizado pocos estudios que consideren múltiples variables que afectan el espectro de gotas producto de la aspersión del herbicida. Los objetivos de este estudio fueron elucidar los efectos del tipo de boquilla, el tamaño del orificio, el ingrediente activo del herbicida, la presión, y el volumen de aplicación sobre el espectro de gotas de la aspersión del herbicida. Los datos del espectro de gotas fueron colectados para 720 combinaciones de variables de aplicación-aspersión, las cuales incluyeron seis soluciones de aspersión (cinco herbicidas y agua sola), cuatro volúmenes de aplicación, cinco boquillas, dos tamaños de orificio, y tres presiones de operación. El estudio de laboratorio fue realizado usando un instrumento Sympactec de difracción láser para determinar las características del espectro de gotas para cada combinación de tratamientos. Al promediar los resultados por efecto principal, el tipo de boquilla tuvo el mayor efecto en el tamaño de gota. El ranking de tamaño de gota para boquillas, de más pequeña a más grande, usando valores de diámetro medio (Dv0.5), fue XR, TT, AIXR, AI, y TTI con 176% de cambio en los valores de Dv0.5. En promedio, el incrementar el tamaño del orificio de la boquilla de un orificio 11003 a uno 11005 aumentó los valores Dv0.5 en 8%. Cuando se comparó con el tratamiento con agua, cloransulam (FirstRate) no cambió el valor de Dv0.5. Clethodim (Select Max), glyphosate (Roundup PowerMax), lactofen (Cobra), y glufosinate (Ignite) redujeron los valores de Dv0.5 en 5, 11, 11, y 18%, respectivamente, cuando se compararon con agua al promediarse sobre las otras variables. El incrementar la presión de las boquillas AIXR, TT, TTI, y XR de 138 a 276 kPa y la boquilla AI de 276 a 414 kPa disminuyó el valor de Dv0.5 en 25%. El aumentar la presión de 276 a 414 kPa y de 414 a 552 kPa para el mismo grupo de boquillas y la boquilla AI disminuyó Dv0.5 en 14%. El volumen de aplicación tuvo el menor efecto en el valor de Dv0.5. Al aumentar el volumen de aplicación de 47 a 187 L ha−1 se incrementó el valor de Dv0.5 en 5%, indicando que el tamaño de gota de los herbicidas evaluados no fue altamente dependiente del volumen de aplicación. El efecto sobre el tamaño de gota de las variables examinadas en este estudio de mayor a menor efecto fue: boquilla, presión de operación, herbicida, tamaño del orificio de la boquilla, y el volumen de aplicación.

A synthesis of 93 hydrologic records from across North and Central America, and adjacent tropical and Arctic islands, reveals centennial to millennial trends in the regional hydroclimates of the Common Era (CE; past 2000 years). The hydrological records derive from materials stored in lakes, bogs, caves, and ice from extant glaciers, which have the continuity through time to preserve low-frequency ( > 100 year) climate signals that may extend deeper into the Holocene. The most common pattern, represented in 46 (49 %) of the records, indicates that the centuries before 1000 CE were drier than the centuries since that time. Principal component analysis indicates that millennial-scale trends represent the dominant pattern of variance in the southwestern US, northeastern US, mid-continent, Pacific Northwest, Arctic, and tropics, although not all records within a region show the same direction of change. The Pacific Northwest and the southernmost tier of the tropical sites tended to dry toward present, as many other areas became wetter than before. In 22 records (24 %), the Medieval Climate Anomaly period (800–1300 CE) was drier than the Little Ice Age (1400–1900 CE), but in many cases the difference was part of the longer millennial-scale trend, and, in 25 records (27 %), the Medieval Climate Anomaly period represented a pluvial (wet) phase. Where quantitative records permitted a comparison, we found that centennial-scale fluctuations over the Common Era represented changes of 3–7 % in the modern interannual range of variability in precipitation, but the accumulation of these long-term trends over the entirety of the Holocene caused recent centuries to be significantly wetter, on average, than most of the past 11 000 years.

Efforts to disseminate heat-related illness (HRI) prevention practices among Latino farmworkers represent a critical occupational safety strategy in Florida. Targeted initiatives, however, require understanding the workplace dynamics that guide agricultural safety behaviors. This article reports focus group data collected in 2018 from citrus harvesters in central Florida and provides an in-depth perspective on the workplace culture that shapes their implementation of heat safety measures. Results indicate that citrus harvesters regularly suffered HRI symptoms yet rarely reported or sought treatment for their injuries. In some cases, the risks of developing HRI were accepted as a facet of agricultural work and harvesters blamed themselves for their illnesses. Implementation of safety practices hinged less on knowledge than on the availability of water and rest breaks and the quality of employer-employee relations and exchanges. Thus, trust was a determinant of workers’ attitudes toward management that contributed to a harvesting operation’s safety climate. Results highlight the difficulties of putting into practice measures that are not rewarded by the workplace culture and suggest that the extent to which intervention strategies promote not only individual safety behaviors but organizational accountability may predict their effectiveness.

Holocene climate reconstructions are useful for understanding the diverse features and spatial heterogeneity of past and future climate change. Here we present a database of western North American Holocene paleoclimate records. The database gathers paleoclimate time series from 184 terrestrial and marine sites, including 381 individual proxy records. The records span at least 4000 of the last 12 000 years (median duration of 10 725 years) and have been screened for resolution, chronologic control, and climate sensitivity. Records were included that reflect temperature, hydroclimate, or circulation features. The database is shared in the machine readable Linked Paleo Data (LiPD) format and includes geochronologic data for generating site-level time-uncertain ensembles. This publicly accessible and curated collection of proxy paleoclimate records will have wide research applications, including, for example, investigations of the primary features of ocean–atmospheric circulation along the eastern margin of the North Pacific and the latitudinal response of climate to orbital changes. The database is available for download at https://doi.org/10.6084/m9.figshare.12863843.v1 (Routson and McKay, 2020).