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Ali Tamizi, Ian R. Young, Agustinus Ribal, and Jose-Henrique Alves

Abstract

A very large database containing 24 years of scatterometer passes is analyzed to investigate the surface wind fields within tropical cyclones. The analysis confirms the left–right asymmetry of the wind field with the strongest winds directly to the right of the tropical cyclone center (Northern Hemisphere). At values greater than 2 times the radius to maximum winds, the asymmetry is approximately equal to the storm velocity of forward movement. Observed wind inflow angle (i.e., storm motion not subtracted) is shown to vary both radially and azimuthally within the tropical cyclone. The smallest observed wind inflow angles are found in the left-front quadrant with the largest values in the right-rear quadrant. As the velocity of forward movement increases and the central pressure decreases, observed inflow angles ahead of the storm decrease and those behind the storm increase. In the right-rear quadrant, the observed inflow angle increases with radius from the storm center. In all other quadrants, the observed inflow angle is approximately constant as a function of radial distance.

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Jose-Henrique G. M. Alves, Scott Stripling, Arun Chawla, Hendrik Tolman, and Andre van der Westhuysen

Abstract

Waves generated during Hurricane Sandy (October 2012) contributed significantly to life and property losses along the eastern U.S. seaboard. Extreme waves generated by Sandy propagated inland riding high water levels, causing direct destruction of property and infrastructure. High waves also contributed to the observed record-breaking storm surges. Operational wave-model guidance provided by the U.S. National Weather Service, via numerical model predictions made at NOAA’s National Centers for Environmental Prediction (NCEP), gave decision makers accurate information that helped mitigate the severity of this historical event. The present study provides a comprehensive performance assessment of operational models used by NCEP during Hurricane Sandy, and makes a brief review of reports issued by government agencies, private industry, and universities, indicating the importance of the interplay of waves and surges during the hurricane. Performance of wave models is assessed through validation made relative to western Atlantic NOAA/NDBC buoys that recorded significant wave heights exceeding 6 m (19.7 ft). Bulk validation statistics indicate a high skill of operational wave forecasts up to and beyond the 3-day range. Event-based validation reveals a remarkably high skill of NCEP’s wave ensemble system, with significant added value in its data for longer forecasts beyond the 72-h range. The study concludes with considerations about the extent of severe sea-state footprints during Sandy, the dissemination of real-time wave forecasts, and its impacts to emergency management response, as well as recent upgrades and future developments at NCEP that will improve the skill of its current wave forecasting systems, resulting in more reliable wave forecasts during life-threatening severe storm events in the future.

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