Note this is a multi-part review of Arthur, with the focus in this post on the validation of marine wind gust forecasts.
Earlier this summer Jonathan posted an analysis of Hurricane Arthur’s Wind Gust Factors for land locations in an effort to evaluate the performance of CSTAR related research to operations activities. This post addresses wind gust factors for marine locations using data from nine buoys off the Southeast, Mid-Atlanitic, and Southern New England coasts (see map below).
Data for this analysis were obtained from the National Data Buoy Center and follow the methodology outlined in a previous post titled “A Wind Gust Factor Database of Marine Observations from 10 Tropical Cyclones.” As a reminder, only observations in which wave data were available with the wave heights less than 5 meters were included. This was done to remove any uncertainty in the quality of the wind observations in large waves. High sea states associated with high surface winds can shelter the buoy and reduce the buoy’s wind sampling (Skey et al. 1995). Also worth noting is that large waves may change the vertical wind profile in the boundary layer. In addition, in strong winds, tethered buoys may be shifted out of the vertical and tilted downwind likely making the wind data unrepresentative.
A total of 331 gust factors were computed for Hurricane Arthur The average gust factor was 1.23 with a median of 1.22. The standard deviation was just 0.06 around the mean of 1.23. The wind speeds ranged from 10 to 44 knots and the wind gusts ranged from 11 to 58 knots.
A key point from this analysis is that the average marine gust factor of 1.23 closely matches the database of 10 tropical cyclones which also found a marine wind gust factor of 1.23 across the study area. Marine gust factors from Hurricane Irene were 1.24, also very similar to the values observed with Hurricane Arthur, which is interesting given the larger wind field with Irene versus the small wind field of Arthur. Future analysis comparing large vs. small wind fields may yield different results and should be explored. However, at this time these results give credence to the default gust factor value of 1.25 in the CSTAR Wind Gust smart tool for marine locations. Hurricane Arthur also demonstrated a notable CSTAR research to operation success of the new CSTAR motivated wind gust forecast methodology.