Officially estimated sustained wind speeds around the eye wall of Hurricane Isaac are 80 mph very early this Wednesday morning. You probably remember that Roanoke’s maximum wind gust in the June 29 derecho was 81 mph. I alluded in the last post to the similarity of wind speeds just to give at least some idea of comparison how the wind was blowing. But let’s resist the temptation to go beyond that in comparing the storms. Roanoke’s 81 mph gust was just that — a gust, not a sustained wind speed. It was the highest officially recorded in Southwest Virginia, and all of National Weather Service-Blacksburg’s forecast area, during the derecho. Wind gusts at Blacksburg and Lynchburg did not break severe criteria of 58 mph. (Scroll down about halfway in the NWS-Blacksburg’s official report on the derecho linked here to see local wind gust reports.) There were certainly much higher gusts away from the official instruments during the derecho, likely 80-100 mph, based on damage (blue dots on the inset map above mark damage or wind measurements of severe force, 58+ mph; black dots are those comparable to hurricane force, 75+ mph). Let’s also remember that when we see gusts reported at various official sites in Louisiana that seem lower than the National Hurricane Center estimates. There aren’t going to be many recording stations where the winds around the eye wall are greatest in the southern Louisiana bayous. Also, while the derecho was 15-45 minutes of straight-line winds out of the northwest, the hurricane will give hours of similar to greater sustained winds shifting from one direction to another. And we didn’t have 1-2 feet of rain and any ocean surge in the derecho. We shouldn’t downplay our derecho — it was a very severe storm system with widespread impact we won’t soon forget — but let’s not try to say our storm was worse than what Louisiana is experiencing. They’re different species, let them live in different meteorological cages.
There’s certainly no comparison between weather in Louisiana and Southwest Virginia this week. A cold front that sank south on Tuesday has reinforced our temperatures with a bit more dryness. Expect highs in the 80s and lows in the 60s, near late August norms, through the end of the week, with little or no chance of rain. The Hydrometerological Prediction Center special map for Hurricane Issac and its remnants, posted Tuesday evenings, shows the heaviest rain curving well west and north of our region. But it also shows rainfall of around 1/2 to 3/4 inch nosing into Southwest Virginia over the next 5 days. This would be related to a weekend cold front that may push some moisture related to Isaac into our region. We are not going to get the brunt of Isaac’s inland rains — parts of Arkansas, Missouri and Illinois will most likely be in the core of that, where it is so dry there is next to no concern about large-scale flooding despite forecasts of 2-5 inches of rain. But we may get a little bit of Isaac’s moisture, eventually.