Weakening Isaac may deliver some moisture to SW Virginia on the rebound
Hurricane Isaac has hit pretty hard in the parishes (what Louisiana calls counties) south and southwest of New Orleans, with some areas there reporting worse flooding than occurred during Katrina. About 600,000 are without power in the region. More on the storm and its ongoing effects linked here from the Associated Press.
There is no “Tropical Landfall for Dummies” book that tropical systems can follow once they make it to shore. Every inland trek of a former tropical system is different. Some wash out almost entirely soon after landfall, becoming barely recognizable. Others continue well inland as an enormous rain producer, but not much else. Some spawn lots of tornadoes, most spawn a few, but others spawn very few or none away from the immediate coast. Some maintain a recognizable circulation for several days, sometimes regenerating if the circulation happens to get back over an ocean (Camille did this over the Atlantic in 1969, after its almost inconceivable dump of terrain-altering rain on central Virginia.) A few line up just right along a boundary between warm and 
cold air and successfully make the transition into a powerful extratropical low-pressure system, capable of producing hurricane-like winds far away from any ocean — the Galveston Hurricane of 1900, Hazel in 1954, Opal in 1996, Ike in 2008 are a few examples of that. Perhaps the most common thing a tropical system will do inland is slowly see its moisture sheared off from the circulation center, which then kind of dawdles around and slowly dies, cut off from any meaningful energy source. That appears to be the likely fate of Hurricane Isaac. Slowly and surely, it will wobble northward up the Mississippi River Valley, its moisture gradually becoming more unwound from its circulation center, and eventually pulled loose along a cold front sinking southeastward into the Upper Midwest and the Ohio Valley. The C-shaped pattern of the Hydrometerological Prediction Center forecast map shows the expected area of heaviest rains during the next 5 days, coming directly over some of the driest agricultural lands in the country, where many rivers are at near record lows and not expected to flood even if these amounts verify. At first, the rain will be closely connected to the circulation center of Isaac, but eventually, more of it will get pulled loose ahead of the cold front.
As the front advances south and east and possibly stalls across the Ohio/Tennessee Valley, central Appalachians and Mid-Atlantic, it is possible that some of Isaac’s moisture will find its way to Southwest Virginia. The HPC map even suggests an inch or so of rain may be possible in some of our region by late in the weekend and early next week (Yes, Hokie fans, there may be a chance of Isaac-inspired showers for the season opener with Georgia Tech in Blacksburg on Monday night — hopefully not the stormy mess of 2000 when the same two teams tried to open the season at Lane Stadium.) The HPC weather map for Sunday morning still shows the remnant low of Isaac centered over Illinois, weakening but riding the front. While this front will likely not provide a sharp enough boundary to help Isaac spin into a powerful inland low, the former Isaac may have enough rotation left to keep spinning southwest winds along the front and over the mountains, bringing some warm, moist Gulf of Mexico air that can be squeezed out by the front and any upper-level impulses that move along it. The short answer to whether Isaac will affect our weather is that it will not directly impact us the way Frances, Ivan and Jeanne did in 2004 or Tropical Storm Lee did last September, moving right at us from the coast with heavy rain and a tornado threat, but a little of what it once was may get mixed up in our atmosphere by late in the Labor Day weekend and enhance our chance of showers.
Until then — more seasonable, mostly dry days with highs in the 80s and lows in the 60s. Perhaps a little better chance of showers by Thursday and Friday as Gulf moisture starts building a bit.
August 29, 2012 - 10:48 PM
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I suppose it should be noted that the new “cone of uncertainty” on Isaac’s remnant low over the next 5 days edges right to about the I-81 corridor in Virginia.
http://www.nhc.noaa.gov/graphics_at4.shtml?5-daynl?large#contents
One very critical difference between Isaac and Camille, besides of course intensity at landfall (Cat 1 vs. extreme Cat 5), relative to flooding potential in Virginia: Isaac’s old circulation center is expected to be at its closest point to Virginia on Monday, 5 days from now, and probably not in the state. Camille hit the Gulf Coast on Aug. 17 and crossed Virginia on Aug. 19, just 2 days later. Each passing day between landfall and arrival somewhere inland reduces its tropical characteristics.
Kevin, you have given us an absolutely sane, objective, historically accurate summary of what becomes of tropical systems over land. This is the best statement I have ever seen. You tell us so much in so few words. You have described exactly how it has been and is going to be, and you have injected no emotional overtones. This is how weather reporting and forecasting ought to be done. Bless you.
Three observations from one who is still shaken by frightful memories of Camille:
1. The “cone of uncertainty” is huge this morning. This may be the largest diameter I have ever seen drawn by the NHC.
2. This morning’s model tracks have turned to mush. While the BAMS continues to steer Isaac’s remnants over southwest Virginia, all the others spiral into meaninglessness.
3. The NHC stands out with its insistence upon a more northernly route.
http://www.skeetobiteweather.com/picservice.asp?t=m&m=09&av=4
Meanwhile – looking at the Atlantic visible satellite image – what is at 15 North and 45 West? Is that Kirk? or a new storm?
Thanks, Lexingtonian.
I’ve seen tropical systems go to both extremes — folks eagerly expecting inland rain in dry areas getting disappointed when it suddenly dissipates into nothing, and extreme flooding in locations that weren’t expecting it when the system resurges or tracks differently or interacts differently with an inland feature than what was projected. So we have to keep a close eye on Isaac and what’s left of it. I don’t think it will be a Camille (1969) or a Juan (1985) and have a sudden burst of flooding downpours over Virginia, or an Agnes (1972) and spread a wide swath of extreme rain over several states, or an Ivan (2004) and spin off more than 100 tornadoes, but we don’t know that yet.
Kirk is farther north than that, Doppler Carol. You’re likely seeing the system circled in red that is given a high chance of development … quite likely the future Leslie. It has a chance to move closer to the U.S. than Kirk, so it’s worth a watch, though most early indications are it too will curve out to sea.
http://www.nhc.noaa.gov/gtwo_atl.shtml
HPC has shifted its core of heaviest rainfall just a tad southward in the Ohio Valley, a little closer to us, sort of angling southeastward a bit. Expecting Isaac’s moisture to be wrung out along a stalling front in that area. Folks familiar with 1985 flooding that killed 10 in the Roanoke Valley may remember that was what happened with Juan’s moisture in this area. The Ohio Valley, though, is far, far from saturated like our area was in ’85.
http://www.hpc.ncep.noaa.gov/tropical/qpf/tcqpf.php?sname=Isaac
It was a dry August at my house…….about 1.50. I’ll need a good September to make up for that, and to ensure some good fall colors.
My daughter’s third birthday party is Saturday afternoon. Should I expect Isaac rains to be an uninvited guest ?
Isaac shouldnt have much effect on us by Saturday, but there may be a few normal late summer pop-up storms as humidity begins to build. Happy 3rd birthday to your daughter from the father of a 2 1/2 year old son!
My hubby and I are leaving this evening, bound for Atlanta for the Chick-Fil-A kickoff game. At this point, should we expect to run into any rain as we head south? We are making our way back to Virginia early Saturday in hopes of avoiding the drenching rains.
I was watching television at some point today (how weak is that? I cannot remember if it was before DVGC at Oh-Dark-30, or at Draper when I stopped by the clubhouse a couple of times, or who knows?), but I saw that NOAA has now named Leslie as a 40 MPH trop storm.
BTW, and you may have mentioned this above KM, I looked at the link to the AP story about the effects of Isaac, and the number of folks …. check that, “homes and businesses” …. without electricity had risen to 900K. And that was just in Louisiana. In the 22nd paragraph. But if most or even many of those outages are simply from downed transformers (as opposed to snapped lines, poles, or worst of all, heavily damaged substations), perhaps a lot of those outages can be repaired fairly quickly, as in 2-3 days. And the power companies hopefully had time and the foresight to get the crews in safe proximity (unlike Mr. Derecho of June 29th) so that once the rains and floodwaters subside, repairs can begin.
Comments, folks. Somebody who drops in here once in a long while — and he is a beloved (by Sam Oakey and me, at least) “snow hater,” too — can add his experience and expertise on the above.
Ok, Rick, I’ll be rooting for you to get abundant (but not flooding) rains in the next few weeks. I had no idea things had become that dry for you and perhaps others down that way. I had close to 3 inches in August, thanks to 1.3 inches on the 19th and an extra 0.7 some time between that evening and the 21st. I could use some more rain, but the ol’ lawn looks an awful lot better now than 365 days ago.
Draper overall looked OK, but I could not get a good feel for how the non-watered parts of the golf course and the lawns of homes nearby looked, because it was so foggy. Visibility was about 1/3rd mile when I arrived and for the first few holes, but then got thicker!! By the time I played 8th, 9th, and 10th I could see where long shots started off, but could not see them land. But then things improved. Got sunny on the 18th hole. The creeks had water in them, but were not flowing very well.
Here comes the cool spell……………though you must wait at least another week.
http://www.cpc.ncep.noaa.gov/products/predictions/814day/814temp.new.gif
Look at this.
Now most of the model runs aim the remnant of Isaac at Virginia. Even the NHC has moved its blue line down to our direction. Instead of pointing toward PA, it is pushing through WV to us.
Of course, the thing may have rained itself out before it gets this far.
http://www.skeetobiteweather.com/picservice.asp?t=m&m=09&av=4
Rather than rain itself out, it probably will just stretch the rain out.
The fact that it may be interacting with a stationary front is something to watch. Tropical systems bumping up against stationary fronts have a history of some locally intense downpours.
Looks like we get a heat spike on Friday, with a day of high pressure parked overhead and light westerly downslope winds. Low-mid 90s Roanoke and east; mid-upper 80s to west, below 3,000 feet.
Also looking more and more like we have our second Labor Day in a row dealing with tropical remnants. Tropical Storm Lee soaked us — and spawned a tornado that damaged a gas station in Carroll County — last Labor Day.
Have us for 95 tomorrow and 90 on saturday! Blah, thought this crap was over with! Glad to see that cool weather moving in on the 10 day outlook! Kevin, are we looking at possible temperatures in the 50s for us here in central Virginia when that moves in? Hopefully that will finally put an end to the chances of these 90 degree days.
National Hurricane Center has issued its last public advisory on Isaac at 4 p.m. The last “cone of uncertainty” has our part of Virginia near the center 5 days out, with the projected location of Isaac’s remnant low in West Virginia.
http://www.nhc.noaa.gov/graphics_at4.shtml?5-daynl#contents
Jared: 90-degree weather is usually not over at the end of August. Roanoke averages 4 90-plus days each September, and has had at least 1 in about three-quarters of its Septembers dating to 1912. I would suspect Greene County would have similar numbers.
Any below-normal air mass moving down from Canada now would deliver widespread 50s, perhaps some 40s, for lows. Let’s see what that looks like in a few days after we get past the Isaac invasion over Labor Day.
A few comments. First, tomorrow. WAHH!!! Nick alertly pointed out that often WSLS-10 is more “optimistic” about temps, forecasting warmer highs than “7″ and “13.” Not so tomorrow, although it could be because Ms. Corfont did the WSLS forecast instead of Jeff H. Per “10″: ROA high of 91. WDBJ7: 95!!! Are you kidding me? BOOOO. NWS: 94!!
According to R. Reed, the hot temps will increase the chances of t-storms. Rick, may you and anyone else who is getting really dry get one manana. There is a t-storm just south of clarkdocvet right now, just west of Galax (or did it hit you, Veterinary Man?)
Shifting to the Plains, Kans. City was at 98 degrees a few minutes ago. Could all that hot air increase the chance of tornados once Isaac’s moisture reaches that far north?
I just had a recollection. Back many Septembers ago, probably the ridiculously wet Sept. 2004, all that wetness (from the remnants of several hurricanes) introduced so much moisture into SW Virginia that the low temps that month were very high, and even the sunny days were very muggy. Autumn was very late, whichever year it was. Whichever year it was, the first date with a high in the low 50s here in Roanoke was very late.
Just consulted one of my bookmarks, “Daily Climate Data,” and sure enough it was the autumn of 2004. First day in ROA that had a high below 55? Nov. 10th. First day with a high below 50? Nov. 26th, with a high of 49. I also think that was still another year with very little snow here in ROA.
This is a little like that day in late July … July 26, to be precise … when we had a 1-day heat spike, all the way to 98 in Roanoke, bracketed by 2 days of low 90s on either side. It’s a single day when conditions are lining up for hotter weather, especially the light westerly downslope wind (which may work against the daytime heating on storm chances — kind of a push and pull there).
On radar now: A narrow line of storms moving north west of Jackson Kentucky is connected to Isaac’s circulation. In fact, it is an outer band of Isaac..
Arkansas gets ready..
But i dont think you-ll have to hoard Rice Crispies.
http://in.reuters.com/article/2012/08/30/us-markets-isaac-rice-idINBRE87T14J20120830
also here is a view of historical tracks of remnants over our pal Kevins
Home Weather Grounds..
http://localtvkfsm.files.wordpress.com/2012/08/tracks1.jpg
and this.
http://nwahomepage.com/fulltext-news?nxd_id=361112
Yep,Doug it poured down in Galax late this afternoon,but at my house east of the city by 6miles,not a drop!! Fickle mother nature she is…
Doug: 2004-05 was a middling winter, 16 inches for Roanoke, about half of it in the Feb. 27-28 snowstorm that winter, and another 3 inches in March. So it was definitely a slow-starting winter.
Joe: Thanks for the story on rice farming in Arkansas. My father was a parts/inventory supervisor for a large rice mill for 2 decades (before that, he did hard manual labor, throwing heavy sacks of rice hulls and such). Interesting that the drought has been good for rice farmers — the rice is flooded by water pumped from underground aquifers to limit insect infestations, and it grows nicely in the hot sun. Now they’re racing against the drought-busting rains and the unwelcome tropical breezes.
I’ve heard that heavy rain may actually destroy what little corn crop there is farther north in Illinois, too. Always too much or too little rain when it comes to farming. If my father had pursued his first career instincts, he might have been a farmer, and I would have inherited the acreage today, either directly overseeing it or hiring/renting it out to others.
New HPC rainfall estimates from Isaac/frontal interaction for our region: 2-3 inches next 5 days.
http://www.hpc.ncep.noaa.gov/tropical/qpf/tcqpf.php?sname=Isaac
It would be great to see u guys get a couple days of
steady rains..
Pretty those trees up for my visit..
and loosen up that red clay for a salad patch.
..and Kevin..you are quite welcome.
I guess we do the work thats around us.
Hats off to your dad for hanging with it.
My back wouldnt have lasted with the sacks of rice.
Carrying shingles and lumber gavce me the gait I have now.
There could be a localized disaster about to happen. FOX NEWS just told of a dam at the southern end of Lake Tangipahoa (no, it is not in Hawaii — although it sure sounds like a Hawaiian word) in SW Mississippi, just west of the town/city of McComb. There is real fear that that dam may break, which would spell disaster for everyone down river, especially the towns of Kentwood and Roberts, Louisiana (just south of the border). I think they reported that some waters have already escaped from the dam (overflowed?), but for now the dam is holding.
FOX is also reporting from Slidell, LA, just east of New Orl’ns. They were victims of the storm surge in Katrina, but the flooding is worse from Isaac. Earlier today I saw a great map on TWC that showed estimated rainfall totals throughout Ark., Louisiana, and Miss., and there were two areas that were shown in white, meaning 15+ inches had fallen. One was tiny in Slidell, and the other area was actually wider and was just a few miles east of Biloxi, MS.
Kevin …. or Joe, or Quags if you are back in the USA now …. any chance of showing one of those accumulated rainfall maps for that part of the US either later tonight or tomorrow? Meaning Louisiana, Mississippi, coastal ‘Bama, and Arkansas at least.
The 18Z GFS goes bonkers with rain in Virginia, through next 5 days (120 hours).
http://tinyurl.com/9rusor8
I found a track map for Camille. Everything I had seen before bedtime that night pointed straight north. This unexpected turn to the east by a remnant made history.
This is why I shuddered when I saw the earliest projections of Isaac’s track several days ago.
http://www.nhc.noaa.gov/outreach/history/camille_1969_map.gif
Well, actually: Looking on the hurricane tracker map below dating back to 1851 (I used Roanoke as the target location), Camille is really the only fairly close analog for the projected track of Isaac.
http://www.csc.noaa.gov/hurricanes/#
Tropical systems don’t typically curve from the central U.S. east or southeast toward SW Virginia. Usually if they get as far north as St. Louis’ latitude, they are swept NE into Canada. The front is going to block this one from doing that.
The GFS seems to be wanting to pump up the rains on the east side of the Blue Ridge as it approaches. 2-3 feet of rain in 6 hours isn’t at all likely — considered a 1,000-year event. But it’s never smart to take one’s eyes off tropical systems, even if they fade out a day or two (which this one isn’t expected to do).
Camille’s rainfall wasn’t all that impressive coming through Tennessee and Kentucky, as this map shows.
http://www.encyclopediavirginia.org/media_player?mets_filename=evm00000985mets.xml
One thing that’s important to remember with inland tropical systems: Strength at landfall isn’t a very good indicator of potential flooding inland. Agnes in 1972 was a Category 1 hurricane and caused immense and widespread flooding in much of the East. Juan in 1985 was a Category 1 hurricane and eventually triggered the severe flooding in western Virginia and vicinity. Katrina, an enormous Category 5 hurricane before dropping off to Category 3 at landfall, really wasn’t exceptional once it got inland. So Isaac “only” being a Category 1 doesn’t really mean much with respect to rainfall inland.
Kevin if we end up getting 5 inches like, any thoughts on timing and stretching out. For instance 1″ on Sun, 2″ on Mon, 2″ on tues. Or 3 on Mon, 2 on Tues. or 5″ in 24 hr period. Or 1 incheach day?
Bulk of it appears targeted for Monday-Tuesday right now. That’s about as precise as it can be pinpointed at this point.
Yessir, Lexingtonian, about a week ago I used a link that KM provided here (and made it one of my bookmarks) that allows a person to choose any city in the eastern USA and it will show the tracks and years and names of all hurricanes that have gone within a specified number of nautical miles of that city (65 is the default setting). So I clicked on ROA of course, and found that one totally weird storm track that was Camille that “invaded” from the west. I too was shocked that some early estimates of Isaac’s track mimicking Camille, but then the past few days tracks have showed it going into Illinois, Indiana, etc. But starting about yesterday some have showed it doing a Camille, at least with its rainfall. This link that the champion “Link-Man” (KM, of course) posted at 7:53 is a shocker. I am hopeful that it won’t verify THAT much. Like lots of us, I would be glad to get 2 to even 4 inches from the remnants of Isaac, but what that showed is too much. We will just have to wait and see.
But I doubt that it would be anything near as bad as the once-in-ten-generations type of event that Camille was. As KM pointed out, Camille got to here in Virg. in just two days after landfall. And it was the most powerful hurricane to make landfall in the lower 48 since at least the 1935 Florida Keys hurricane, I am pretty sure. Category 5 at landfall.
3 quick notes perusing the Euro model:
(1) By Monday there really isn’t any discernible circulation from the former Isaac, it just washes out in the Ohio Valley and gets pulled into the front/low-pressure trough. It does pull winds around to south and southeast for a considerable period of time, though, which would build moisture.
(2) The cool air push from Canada is quite apparent about 8-10 days out.
(3) It brings what is now Tropical Storm Leslie very close to Cape Cod/Maine 10 days out.
Kevin, does the Euro show the projected path that Leslie might take? Does it basically travel west to just short (east) of the Bahamas, then head roughly due north to New England, never making landfall until then? Because that was the path of the Great New England Hurricane of September 1938.
Could we have two hurricanes in 2012 that followed the paths of two of the most historic hurricanes in U.S. history? Doubtful. And even if one of them does do the mimic thing, here is hoping that it is nowhere as destructive and lethal as the originals.
The 12Z Euro has Leslie tracking much farther east than what you described, Doug, then getting pulled closer to New England by the same upper-level trough bringing down the cooler air from Canada into the central/eastern U.S. You can see it on the link below, the tight circles east of New England.
http://blogs.roanoke.com/weatherjournal/files/2012/08/LeslieDay10.gif
Thanks again, Kevin. Unless that hurricane were tracking NW, it looks like it would smash into Halifax, Nova Scotia. But of course the odds are it won’t go anywhere near there anyway.