UPDATE 3:40 PM, 8/28: Westward track shift with Isaac would mean less chance of direct effects in Southwest Virginia
UPDATE 3:40 PM: Isaac has been a hurricane — barely, with 75 mph winds — since midday. It will come ashore this evening or early Wednesday likely as a minimal hurricane … but that will still bring hours of wind comparable to our June 29 derecho for those in the eyewall. All indications remain that Isaac’s remnants will track well west of our region Showers and storms this afternoon and evening will be spotty with a passing cold front END UPDATE
UPDATE 7:30 AM, 8/28: Isaac still hasn’t gained his hurricane stripes this morning, rated as a strong tropical storm with 70 mph winds as of this update. That could change at some point today, but as you can see from the satellite photo at left, Isaac’s structure is far from textbook. There is an obvious eye-like structure, but it’s open on the north side. Isaac has been sucking in a bit too much dry air to develop a full eyewall structure that would enable rapid development. There is still time before it runs into Louisiana later today, and even as a strong tropical storm/minimal hurricane, storm surge and some wind damage will be a problem. Plus, Isaac may slow down some upon landfall, causing torrential rainfall over the same location before its remnant low makes a track northward through the drought-stricken central U.S., where his arrival will be heralded, not scorned . Closer to home, we have a weak cold front pushing through today is already triggering a few showers. With some daytime heating, and even a bit of moisture blowing in from the southeast aided by Isaac’s circulation, a few sporadic storms may develop during the afternoon. END UPDATE
UPDATE 10 PM: As of this update, Isaac still isn’t considered a hurricane. That may change soon, perhaps at the 11 p.m. update — click on the National Hurricane Center website linked here for the latest. It’s on track for a Louisiana landfall and, likely, a rather slow trip northward with its remnant low through through the Mississippi River valley, well west of us. If we get any moisture from Isaac, it will be second-hand, pushed our way by a cold front over the weekend or early next week. We’ll have a rather run-of-the-mill cold front on Tuesday that may trigger some showers. Highs in the 80s and lows in the 60s will continue most of this week. END UPDATE
At left is Sunday evening’s cluster of forecast tracks from various hurricane models used by the National Hurricane Center. The most notable thing is that only one track for Tropical Storm Isaac (very likely soon to be a hurricane) is as far east as Mobile, Ala., and only two others are east of New Orleans. Forecast guidance has mostly continued to shift westward today with the track of Isaac throughout Sunday. (The European model is an exception, depicting a direct hit on Mobile. Meanwhile, the GFS has the hurricane almost getting to the Texas-Louisiana border). This westward shift means a few things. (1) The Mississippi Gulf Coast, New Orleans and even the Louisiana coast west of New Orleans are having to prepare much more for a possible hurricane than it appeared they would just 24-48 hours ago. (2) The farther it goes westward, the longer it stays over the warm Gulf waters, and therefore the more chance it has for an explosion of development that could carry it into “major hurricane” status at Category 3 or above (111+ mph winds). Sunday evneing National Hurricane Center projections are for a Category 2 hurricane at landfall. (3) A landfall west of Mobile, combined with northwest movement at landfall, would likely carry the remnant low of Isaac farther west once inland, into Arkansas or even Oklahoma (areas with extreme to exceptional drought), and its eventual curve back eastward with a upper-level trough in the central U.S. may carry it well north of Virginia through the Ohio Valley. That would likely mean less chance of direct effects here, such as heavy rain and tornadoes — though there could be some indirect effects worth keeping an eye on. (4) The more westward track will carry it even more deeply into the nation’s oil extraction and production hotbed, and you know what that will mean at the gas pump.
Southwest Virginia weather is going to be benign, by comparison to the Gulf Coast, this week, as our weather is controlled mostly by high pressure. Expect highs mostly in the 80s, lows mostly in the 60s, near normal for late August, perhaps even creeping a little above normal. Shower/thunderstorm chances will be the typical sporadic afternoon stuff, though a weak cold front Tuesday may enhance those chances a bit. In general, we will be moving toward warmer and stickier weather this week after 2 weeks of mostly below-normal temperatures. I wouldn’t be surprised to see a 90-degree high at Martinsville or even Roanoke a day or two this week, perhaps even on Monday.