Standardization and Assimilation of Surface Wind Observations During Land-falling Tropical Cyclones

Standardization and Assimilation of Surface Wind Observations During Land-falling Tropical Cyclones

Marty J. Bell, Director of Research and Modeling, WeatherFlow, Inc. mbell@weatherflow.com, (970) 818-7635, Corresponding author Forrest J. Masters, Associate Professor of Civil and Coastal Engineering, University of Florida, masters@ce.ufl.edu, (352) 294-7792

Submission to the 32nd Conference on Hurricanes and Tropical Meteorology 18 – 22 April 2016 San Juan, PR

Abstract

Despite more than a half century of advancements in boundary layer research and anemometric technology, surface wind speed data collected by ASOS, AWOS, NDBC and other mesonet systems are widely used without any correction for variations in site conditions and hardware configurations. The consequence of overlooking the effects of observation height, upwind fetch (terrain and topography), instrument response characteristics, and data acquisition methods can be significant. For example, the literature has shown that ‘raw' gust measurements measured at airports can under-predict equivalent values for true open exposure conditions by as much as 40% (Powell et al., 1996; Masters et al., 2010). Such biases limit the ability to assimilate these observations into numerical models. This paper describes the joint efforts of the Florida Coastal Monitoring Program (FCMP) and WeatherFlow to improve weather informatics, specifically as it relates to analyzing surface weather conditions in terrestrial and near-shore environment during landfall of Atlantic tropical cyclones.

The FCMP is a joint university consortium that deploys adaptive mesonets in the path of land-falling Atlantic Tropical Cyclones to conduct wind engineering and boundary layer research (Balderrama et al., 2011). The current focus of the program is to collect high-fidelity wind speed measurements in suburban and urban terrain to better characterize turbulence conditions in the built environment. WeatherFlow owns and operates the second largest private mesonet in the CONUS, including a network of 400+ coastal stations, 89 of which are in its hurricane hardened network (HurrNet) designed to withstand extreme wind loading. Data are ingested into WeatherFlow's StormPrint model, an application of the WRF-ARW numerical weather prediction model and the Gridpoint Statistical Interpolation (GSI) data assimilation tools, to produce fine-mesoscale surface wind fields. Raw data are processed in real-time using the objective estimation technique described in Masters et al. (2010). Directional roughness lengths are estimated from several years of historical records from permanent weather stations (i.e. gusts and mean wind speed reports) and high-resolution time series data from the adaptive mesonets. Data are then converted to a prescribed metadata format (i.e., height, terrain, and short duration average). This approach is fully automated and can be applied to a wide range of surface weather station types located in a large region.

This paper will explore the value of its tool in operational forecasting, emergency management, and meteorological and wind engineering research. The common data collection procedures applied in adaptive and fixed weather station networks will be reviewed, followed by a detailed discussion about the operational logistics for deployment and analysis. Case studies from recent hurricanes will be presented to demonstrate the efficacy of this approach to produce accurate representations of the surface wind field. Finally, we will explore the state of observing technology in a practical context and describe a path forward to unify research and operations across multiple fields.

References

Balderrama, J.A., F.J. Masters, K.R. Gurley, D.O. Prevatt, L.D. Aponte-Bermudez, T.A. Reinhold, J.-P. Pinelli, C.S. Subramanian, S.D. Schiff, and A.G. Chowdhury, 2011: The Florida Coastal Monitoring Program (FCMP): A review. Journal of Wind Engineering and Industrial Aerodynamics, 99(9), 979-995.

Masters, F.J., P.J. Vickery, P. Bacon, and E.N. Rappaport, 2010: Toward objective, standardized intensity estimates from surface wind speed observations. Bulletin of the American Meteorological Society, 91, 1665-1682.

Powell, M. D., S. Houston, and T. A. Reinhold, 1996: Hurricane Andrew's landfall in South Florida. Part I: Standardizing measurements for documentation of surface wind fields. Wea. Forecasting, 11, 304–328.