Larry Brown at our office put together some interesting statistics from Irene here is his post.
For more specifics and detail see the attached graphs, but as an overall summary what verified was a gust factor of about 1.4 to 1.65 over land sites (with little change in the gust factor for varying wind directions at RIC….to a much more significant change in gust factor with wind direction at NGU. At NGU…the gust factor was generally 1.3 to 1.4 when winds were NE…then 1.6 to 2.0 when winds shifted to the WSW. At the true marine site RPLV2, there was basically no change in gust factor with wind direction, generally remaining a rather low factor of 1.15 to 1.20 throughout the event. At CHYV2 the gust factor was very dependent upon wind direction…a significantly higher factor (1.5-2.0) (although not necessarily higher wind speeds) when the wind direction was off land late in the event (NW to SW)…and significantly lower factor (1.2-1.35) when the wind direction was off the water (NE).Note that most of our land sites, outside of perhaps ECG and points twds the coast in NC, sustained tropical storm force winds/40 mph+ were almost non-existent (or only lasted for a few hrs) which would suggest TCM wind grids (even those issued during the day Sat) required about a 40-50% reduction factor over land to verify (in some cases even more). However, a high gust factor was required since peak gusts at most places reached 60 mph or higher.
I have not shown graphs from Isabel here but overall conditions were not that much different with respect to gust factor (a bit lower but still fairly high over land). The track was different and therefore winds never really shifted to a westerly direction during the event. Once again though, sustained winds over land were barely into the tropical storm forec range…while peak gusts were to 75 mph or higher across most of our inland CWA.