The National Weather Service at Blacksburg has not reset its storm total radar composite (linked here) since Saturday, so it gives a good picture of the spotty nature of rains we have experienced with the remnants of Hurricane Isaac. My house is in one of the light blue areas under 0.30 inch. This picture has changed some even Wednesday — most of the green 1-2-inch area just north of Roanoke was colored in Wednesday evening in a stalled squall that led to a flash flood warning for southwest Botetourt and northeast Roanoke counties for a while. Overnight, the color scheme may change a little bit, as a disturbance works in from the west with scattered showers and maybe a few storms, slowly diminishing remnants of what was once a fairly stout squall line in the Ohio Valley earlier today.
We can finally stop talking about former Hurricane Isaac — and start talking about possible tropical storm Nadine. The chip off the old block is (as of late Wednesday evening) given a 50 percent chance of becoming a tropical cyclone in the Gulf of Mexico. Being a tropical cyclone doesn’t necessarily mean it will be named — it may only become a depression — but the National Hurricane Center on its Facebook page already has a rather lengthy explanation of why it would be given the name Nadine and not regain the name of the former hurricane from which it sprang. The hurricane center is expected to send some surveillance flights into the storm on Thursday afternoon to ascertain its organization and strength. Its likely the system will be shunted eastward toward the Florida peninsula as new cold fronts and a southerly dip in the jet stream by the weekend nudge it along. Out farther in the Atlantic are hurricanes Leslie and Michael. Leslie, now poking along, will sweep near or over Bermuda and then speed rapidly in the general direction of Newfoundland. Michael will stay with the fishes in the open Atlantic.
That dipping jet stream and Leslie’s circulation are going to team up to pull down some significantly cooler, drier air from Canada early next week. This temperature anomaly map from the 12Z run of the European model shows blue over much of the East, indicating cooler than normal temperatures by Tuesday morning. Lows in the 50s and highs in the 70s will be widespread, and it may go a little cooler than that in some of the normally cooler spots around, especially if we can get a clear night with calm winds next week. The normal high has dipped below 80 at Blacksburg, with normal lows dropping into the low 50s by next week, and Roanoke’s norms are around 80/60 the next several days, so this is not great chill we’re talking about, just a little taste of fall. When the cold front starts cutting into this leftover tropical moisture, thunderstorms will likely develop, and some of them could be strong to severe. After whatever showers and storms we get overnight, we may get a break in the daily rounds of showers for a couple of days — they will probably be fewer in number over Southwest Virginia on Thursday afternoon, and maybe very isolated or non-existent by Friday afternoon, as high pressure builds in with warmer and somewhat drier air. That high will lead to summerlike temperatures, possibly reaching or exceeding 90 in Roanoke and points south and east one or both of the next 2 days, especially Friday. I’m not about to call this summer’s last stand, but it will be a brief encore performance.