In a previous post, Jonathan discussed a climatological look at gust factors as a function of wind speed for recent storms affecting the study region. The results of the analysis are currently being used to help develop wind gust forecasts for Sandy (2012) in several of the WFOs participating in the CSTAR project. As a quick check to see how these gust factors align with Sandy (2012), I quickly downloaded hourly wind data for Norfolk VA (KORF) for 10/27/08z – 10/29/13z. The wind data represents winds from various directions as the storm continues to track to the north and north west. The image below shows the calculated gust factor as a function of sustained wind speed value (mph).
Consistent with recent results of the CSTAR project, gust factors appear to have a very strong correlation with sustained wind speed, with gust factors gradually leveling off to a value near 1.2 for sustained wind speed values over 30 mph. At wind speeds below 15 mph, these gust factors grow to as high as near 3.0. The general shape of the data closely corresponds to the curve plotted with the climatological data.
I also quickly calculated averages of gust factors as a function of wind direction. Based on the three wind directions represented in this data set, I calculated the following gust factors:
Northerly Wind: 1.47
North easterly Wind: 1.38
North westerly wind: 2.31
This is also consistent with some of the recent results of the CSTAR project, which indicate values near 1.2-1.4 for maritime flow gradually increasing to values over 2.0 for significant fetches over land.