Typical late August weather in SW Virginia as we watch Isaac’s likely path shift west into Gulf of Mexico
Roanoke and Blacksburg were exactly 1 degree below normal for both high and low on Thursday (84/63 on Thursday at Roanoke, 80/57 at Blacksburg). August’s average temperature to date is running about half a degree below normal at both sites now, as the last week’s relative coolness have nudged the numbers down. Temperatures the next week or so are expected to ride amazingly close to normal, with some scattered showers and storms on most days as daytime heating, moisture, terrain effects and upper-level disturbances bubble a few up. A cold front may add some influence to the weather mix by Tuesday … and what is now Tropical Storm Isaac may add its influence by late next week.
Forecast models have come into reasonable agreement over the past 24 hours that the center of Tropical Storm Isaac is likely to travel west of the Florida Peninsula (though it may yet scrape the Florida Keys, perhaps the southwest peninsula, and even Tampa Bay isn’t out of the woods yet when Republicans gather next week), through the central and/or eastern Gulf of Mexico. There, it will find a weakness in high pressure ridging to the north, and also some extremely warm sea surface temperatures, approaching 90 degrees in spots (the reddest areas are up to 31.4 degrees C, or 88.5 F). The high may provide enough upper-level influence to really cut off any winds aloft that could shear the storm, and that may allow a burst of intensification as it moves past Hispaniola and Cuba into the Gulf of Mexico. Isaac hasn’t shown much intensification so far — flights into Isaac have not found an organized inner circulation — but that is expected to change slowly over the next couple of days, especially when the storm is more over water than over the larger Caribbean islands. Most models now do not raise Isaac’s winds into major hurricane territory above 110 mph, but that could change if it spends a lot of time over those warm waters and has favorably calm upper-level winds aloft. Potential effects on Southwest Virginia — heavy rain, tornado threat, maybe even some fairly gusty remnant winds — would likely be maximized if it makes more of a northerly or at least north-northwesterly turn into the Florida Panhandle. The more northwest it tracks, the farther west of about Mobile, Ala., it makes landfall, the less chance we have of heavier rain. However, many models do sweep Isaac’s remnants back to the east with a cold front and/or low-pressure trough late next week. Many details are still in flux before landfall, let alone afterward.