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Charles N. Helms and Lance F. Bosart

tropical disturbances of interest to NHC forecasters. The NHC Invest positions are produced as part of the Automated Tropical Cyclone Forecast system (ATCF, Sampson and Schrader 2000 ) and, as a purely operational product, are not revised during the postseason reanalysis performed by NHC; the 2013 NHC Invest archive can be accessed via the link provided in the data availability section of this paper. Gabrielle first appeared in HURDAT2 at 1800 UTC 4 September 2013. Prior to 1800 UTC 4 September, the

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Alan Brammer, Chris D. Thorncroft, and Jason P. Dunion

sensitivity to the initial AEW trough characteristics and synoptic-scale environmental characteristics highlight the potential difficulties for operational numerical forecasts of tropical cyclogenesis. Komaromi and Majumdar (2015) showed that forecasts of tropical cyclogenesis were sensitive to both the predictability of the forecasted environment as well as the strength and location of the pregenesis disturbances. The eastern Atlantic has also been shown to be a region of high false alarm rates for

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Hui Christophersen, Altug Aksoy, Jason Dunion, and Kathryn Sellwood

1. Introduction Unmanned aircraft systems (UAS) have emerged as an alternative method of collecting weather observations to improve understanding of the tropical cyclone (TC) environment and the accuracy of TC forecasts ( Braun et al. 2016 ; Cione et al. 2016 ), particularly in hazardous conditions where it is too dangerous to operate manned reconnaissance aircraft. The Global Hawk (GH) is one such aircraft that can fly for up to 24 h at an altitude of 60 000 ft (18 288 m) and was first

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Erin B. Munsell, Jason A. Sippel, Scott A. Braun, Yonghui Weng, and Fuqing Zhang

-EnKF intensity forecasts initialized during this period performed poorly, the reasons for intensity error are explored through an analysis of the sensitivity to the sea surface temperature (SST) field and through comparisons between the ensemble simulations and observational data. Section 2 describes the WRF-EnKF setup and operational data utilized, while section 3 presents the composite analyses of Nadine’s track and intensity forecasts with comparisons to the HS3 observations. Finally, section 4

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Erin B. Munsell, Fuqing Zhang, Scott A. Braun, Jason A. Sippel, and Anthony C. Didlake

composite groups of 10 according to their RI-onset time (GOOD: blue; GOOD_EARLY: green; GOOD_LATE: magenta; and POOR: red) and have been extended to 7-day forecasts (the operational real-time system only produces 126-h forecasts). The composite means [thick; positions marked every 12 h in (a)], the NHC best track [black; positions marked every 12 h in (a)], and the 5-day APSU deterministic forecast (orange) are also plotted. The remaining ensemble members not classified in composite groups (other: cyan

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Sergio F. Abarca, Michael T. Montgomery, Scott A. Braun, and Jason Dunion

storm growth ( Maclay et al. 2008 ), there is great interest in developing secondary eyewall forecasting tools. Today, the valuable and sophisticated forecasting tools tend to rely on empirical relationships (e.g., Kossin and Sitkowski 2009 ) and do not necessarily directly incorporate the physical processes of secondary eyewall formation. Secondary eyewall formation dynamics have been the subject of intense contemporary research and contrasting views of the azimuthally averaged dynamics prevail

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Zhining Tao, Scott A. Braun, Jainn J. Shi, Mian Chin, Dongchul Kim, Toshihisa Matsui, and Christa D. Peters-Lidard

Unified Weather Research and Forecasting (NU-WRF) modeling system ( Peters-Lidard et al. 2015 ; Tao et al. 2016 ) to investigate the 24–25 August SAL outbreak. The radiative and microphysical effects of dust and other aerosols on the SAL structure are analyzed. The paper is organized as follows: section 2 provides a brief description of the observational data and model used in this study, section 3 describes briefly the SAL event, section 4 describes the model configuration and experiment setup

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