http://www.nola.com/hurricane/index.ssf/2012/08/tropical_storm_isaac_continues_2.html

Tropical Storm Isaac is taking aim on the northern Gulf Coast. The National Hurricane Center is calling Isaac a significant storm and says surge and freshwater flood threat is expected. The 10 p.m. forecast from the Hurricane Center predicted that Isaac would arrive on the coast as a Category 1 storm, with maximum winds at 90 mph.

NOAA imageTropical Storm Isaac is forecast to strike the Louisiana coast Tuesday afternoon as a Category 1 hurricane.

Isaac is a large tropical cyclone. A dangerous storm surge, heavy rainfall and strong winds extend well away from the center and are expected to affect a large portion of the northern Gulf Coast. The threat of heavy rainfall and flooding is also expected to spread inland over the lower Mississippi Valley region during the next few days.

The storm continues to have trouble organizing. Despite some strong bands of convection that may indicate the formation of an eyewall, dry air in the northeast quadrant of the storm appears to be limiting faster development of the storm. Winds and pressure have not increased significantly over the past several hours.

At 10 p.m., the center of Tropical Storm Isaac was near latitude 27.1 north, longitude 87.0 west. Isaac is moving toward the northwest near 10 mph. This general motion with some decrease in forward speed is expected during the next day or two.

On the forecast track, the center of Isaac will move over the central Gulf of Mexico tonight and approach the coast of southeastern Louisiana and Mississippi on Tuesday afternoon or Tuesday night.

Maximum sustained winds are near 70 mph, with higher gusts. Strengthening is forecast, and Isaac is expected to become a hurricane tonight or early Tuesday, and continue to strengthen until landfall occurs along the northern Gulf Coast.

Tropical storm-force winds extend outward up to 205 miles from the center. The latest minimum central pressure was 979 mb, 28.91 inches.

http://pjmedia.com/weathernerd/2012/08/28/isaac-stubbornly-refuses-to-become-a-hurricane/

Isaac Stubbornly Refuses To Become A Hurricane

August 28, 2012 - 12:10 am - by Brendan Loy

[NOTE: check the blog homepage and follow me on Twitter for the very latest.]
* * * * *

For the third consecutive advisory, the belief that Isaac might imminently become a hurricane was not vindicated at 11:00 PM EDT, as the storm’s winds were held at 70 mph, just shy of hurricane strength — even as the pressure dropped to 979 millibars, which is usually more typical of a borderline Category 1/Category 2 hurricane.

In this sense, Isaac is reminiscent of a poor man’s Hurricane Ike, which at one point had a pressure of 944 mb, typical of a borderline Category 3/Category 4 hurricane, yet its winds refused to budge from 100 mph (borderline Category 1/Category 2). People kept insisting that Ike’s winds would inevitably “catch up” to the pressure, in a burst of rapid strengthening that was always just around the corner. There was also fear that the pressure, plus the storm’s immense size, would lead to an epic storm surge well out of proportion to the winds and category. Similar fears are being expressed with Isaac. Yet Ike’s winds never did “catch up” with its pressure, and the surge underwhelmed — it was a hive, not a pimple.

Likewise, another “I” storm — last year’s Hurricane Irene — at one point had a pressure of 942 mb, typical of a Category 4, but winds of 110 mph that never “caught up” with the pressure. Indeed, Irene eventually weakened to a minimal hurricane, 75 mph, with a pressure of 958 mb (typical of a mid-range Category 3), and then to a tropical storm, 60 mph, with a pressure of 966 mb (typical of a high-end Category 2). Irene, too, produced fears of a storm surge vastly out-of-proportion to its wind and category — yet the reality again underwhelmed.

I’m not saying that Isaac is Ike redux or Irene redux — every storm is different — and I certainly think folks in surge-prone areas should prepare for the worst (or, more precisely, should already have prepared for the worst), including by evacuating if appropriate. But the parallels do give me some pause about the current storm-surge predictions. We shall see.

Meanwhile, I still suspect Isaac will become a hurricane overnight — but I can’t help but wonder, what if my Thursday-morning post, “Might Isaac Never Become A Hurricane?,” turns out to be accurate? I had given up on the notion days ago, but with less than 24 hours until landfall, the storm is running out of time!

In any case, it makes little difference — a 70 mph tropical storm and a 75 mph hurricane are basically the same thing. The question isn’t whether Isaac will become a minimal hurricane, but whether it will have the type of overnight/morning rapid intensification phase, just before landfall, foreseen by the GFS earlier today. It still may. And intensification at landfall would make the storm feel like much more of a beast, as I explained earlier. But every time you think this storm is about to go “rapid,” dry air keeps interfering. That’s very good news for New Orleans & environs, and although I feel a certain dread about the inevitable cries of “OVERHYPE!!!1!” if that good luck continues, it’s obviously best for everyone if it does.

I’ll try to post an update in the morning sometime around 8:00 AM Eastern. Maybe Isaac will finally be a hurricane by then. Stay tuned, as they say.

P.S. One final note. Up until now, talk of various worst-case scenarios, or at least of very-bad scenarios, has been justified and proper, because of the forecast uncertainty and the very real possibilities of calamity that existed. Several people have asserted to me that there was “no evidence” Isaac would become a major hurricane, but that’s just categorically false: multiple reliable computer models had multiple consecutive runs showing a Category 3 or stronger hurricane making landfall on the Gulf coast. Those models weren’t invented by TV pundits or weatherbloggers. They were real, and they were scary. Moreover, although this storm has proven to lack intensity, it’s taking a horrific track from NOLA’s perspective, and if it weren’t for several very persistent dry-air entrainments — something that just can’t be predicted with any degree of certainty — we really could be looking an extremely dire situation right now. This was a close-run thing. The large-scale conditions for strengthening to a major hurricane (good outflow, low shear, warm waters) were nearly perfect; only hard-to-predict small-scale features (dry air, core structure) prevented Isaac from reaching its potential. Meteorologically speaking, particularly in light of the track, this was closer to a disaster than the overhype-troll crowd will ever understand.

However.

Barring significant overnight intensification, the media must dial back the “hype” in the morning. Unless we all wake up to an exploding Isaac that’s finally worked out its dry-air and inner-core issues and is seriously ramping up just before landfall, the worst-case scenarios in terms of intensity will no longer be valid or relevant. So it’ll be time to stop talking about them, and indeed, to explicitly acknowledge that they’re now off the table. Yes, there will still be a significant (though, let’s not kid ourselves, probably not catastrophic) storm surge, plus major threats in terms of inland flooding (that one COULD be catastrophic) and perhaps inland winds, power outages, etc., etc. But those concerns are of a different order from the apocalyptic fears many of us justly felt when we saw model maps like this. It insults readers’ and viewers’ intelligence to treat “ordinary” storm impacts, like typical coastal flooding, downed trees, widespread power outages, gas station roofs blowing in the wind, etc., as epic events of grave significance on par with the sort of impacts we originally feared. This is where media gets hurricanes wrong: not by discussing worst-case scenarios early on, when they’re still plausible and in fact the public needs to be aware of them, but by failing to back off the “hype” once it’s clear that the worst isn’t happening. There’s a reason you’ve seen this blog steadily backing off the worst-case talk today: I always try my best to “keep it real,” and call it like I see it — and it’s become increasingly clear to me that this storm, while very serious (all hurricanes, and near-hurricanes, are!), isn’t going to be an epic catastrophe, after all. It could have been, but now it’s very likely not going to be. I try to make sure my coverage reflects that once it becomes clear. I hope the MSM will do so too.

http://rapidrefresh.noaa.gov/hrrrconus/displayMap.cgi?keys=hrrr:&runtime=2012082720&plot_type=cref_t6sfc&fcst=15&time_inc=60&num_times=16&model=hrrr&ptitle=HRRR%20Model%20Fields%20-%20Experimental&maxFcstLen=15&fcstStrLen=-1&domain=t6&adtfn=1&wjet=1

HRRR Model Fields - Experimental - Tuesday morning 11:00 Central time

and.....

http://pjmedia.com/weathernerd/2012/08/27/isaac-uncertainty-still-reigns/

Just a quick additional note, as an addendum to my post below. There still remains a remarkable amount of uncertainty regarding the details of Isaac’s track, given that we’re only 24-48 hours from landfall. Check out this “4-panel plot” showing the 48-hour positions of the Euro (top left), GFS (top right), HWRF (bottom left) and GFDL (bottom right) models, courtesy of Dr. Ryan Maue and Weather Bell Models:

This particular forecast is, as Maue says, a nightmare. There’s just been much more uncertainty than with most hurricanes, and that remains true, even at this late date.

As an aside, it looks like Isaac may be upgraded to a hurricane — or else very, very nearly one — at 5:00 PM Eastern. Stay tuned.

P.S. Dr. Jeff Masters has some excellent analysis on the potential storm surge from Isaac:

Storm surge is the primary damage threat from Isaac. Isaac is a huge storm, with tropical storm-force winds that extend out 205 miles from the center. For comparison, Hurricane Katrina at landfall had tropical storm-force winds that extended out 230 miles from its center. Isaac’s large size will enable it to set a large area of the ocean into motion, which will generate a large storm surge once the storm approaches land on the Gulf Coast. Water levels at Shell Beach, Louisiana, just east of New Orleans, were already elevated by 1′ this morning. Conversely, water levels have fallen by 2′ this morning at St. Petersburg, Florida, where strong offshore winds due to Isaac’s counter-clockwise circulation have carried water away from the coast. The latest 6:30 am EDT Integrated Kinetic Energy analysis from NOAA’s Hurricane Research Division put the destructive potential of Isaac’s winds near 0.6 on a scale of 0 to 6, but the destructive potential of Isaacs’s storm surge was 2.1 on a scale of 0 to 6. I expect this destructive potential will rise above 3 by time Isaac makes landfall, making Isaac’s storm surge similar to that generated by Category 2 Hurricane Gustav of 2008, which followed a path very similar to Isaac’s predicted path. Gustav brought a storm surge characteristic of a Category 1 hurricane to New Orleans: 9.5′ to Lake Borgne on the east side of the city. A higher Category 2-scale surge occurred along the south-central coast of Louisiana, and was 12.5′ high in Black Bay, forty miles southeast of New Orleans. Recent model runs indicate Isaac may slow down to a forward speed under 5 mph on Tuesday evening and Wednesday morning, close to the coast. If Isaac is just offshore at this time, the coasts of Southeast Louisiana, Mississippi, Alabama, and the Florida Panhandle will be exposed to a large storm surge with battering waves for two high tide cycles. This sort of extended pounding will be capable of delivering more damage than the storm surge of Hurricane Gustav of 2008.

I’m a bit wary of this sort of forecast — likely Category 1 hurricane to produce uncommonly devastating surge due to its size! — because similar predictions regarding Irene in 2011 and Ike in 2008 were not fully borne out by the reality of what occurred. However, the analogy to Gustav seems apt in this case. We shall see. Certainly, if you live in a storm surge zone, take no chances. Get the Hell out; go to higher ground.

Dr. Masters also has a good overview of the surge’s likely impact on New Orleans, including a handy map of the newly upgraded levees. Read the whole thing, as they say.

***

and some data ( Wind speed , rainfall and surge probabilities ) - check forecast for Wednesday ( 36 hour to 1 am Wed ) .... for chances of either Cat 2 ( 21 percent ) and Cat 3 ( 11 percent ) .... as noted above , a lot of uncertainty abounds

Maximum 1-minute Wind Speed Probability Table

Click image to zoom in

[Table of probable wind speed intensity range]

120-Hour Day 1-5 Forecast
Updated: 5:48 PM EDT Monday August 27, 2012
Valid: 8:00 PM EDT Monday August 27, 2012 - 8:00 PM EDT Saturday September 1, 2012

http://www.nhc.noaa.gov/refresh/graphics_at4+shtml/212348.shtml?gm_esurge#contents

Tropical Cyclone Storm Surge Heights
That Have a 1 in 10 Chance of Being Exceeded (NGVD-1929)
Tropical Storm Isaac (2012) Advisory 27
For the 77 hours from 05 PM EDT Mon Aug 27 to 10 PM EDT Thu Aug 30

Select Level:

Map

Satellite

Hybrid

Lat: 45.8288 Lon: -80.6836

Disclaimer

Historical Data:
NHC this storm
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MDL

Description: This application shows storm surge height in feet, above normal tide levels, such that there is an N percent chance of exceeding it, where N ranges from 10 to 90 in intervals of 10 percent. The 10 percent exceedance height, for example, is the storm surge height, above normal tide levels, such that there is a 10 percent chance of exceeding it.

This graphic is based upon an ensemble of Sea, Lake, and Overland Surge from Hurricanes (SLOSH) model runs using the National Hurricane Center (NHC) official advisory and account for track, size, and intensity uncertainty from historical errors. Additional information on the SLOSH model can be found at:http://www.nhc.noaa.gov/ssurge/ssurge_slosh.shtml.

The emergency management community is the primary target audience. However, this product will also be widely used by other federal, state, and local government agencies; the media; maritime interests; and the general public.

Backup Availability and Archive: In the event NHC has difficulty creating the storm surge images, theMeteorological Development Laboratory's Probabilistic Hurricane Storm Surge website maintains the same information. An archive of storm surge products is also available from the MDL website.

Note: You may also read the full description for the Probabilistic Storm Surge Exceedance product at MDL's web page.

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Page last modified: Monday, 27-Aug-2012 21:26:15 UTC

http://www.wunderground.com/tropical/tracking/at201209_5day.html

Five Day Forecast Map

9687

and.....

http://www.nola.com/hurricane/index.ssf/2012/08/isaac_now_forecast_to_hit_new.html

Isaac forecast to hit New Orleans as Category 2 hurricane Wednesday morning, but models still uncertain

Published: Sunday, August 26, 2012, 11:00 PM Updated: Sunday, August 26, 2012, 11:25 PM

By Mark Schleifstein, The Times-Picayune
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Tropical Storm Isaac is on a path that will take it up the Mississippi River on Tuesday and Wednesday through the New Orleans area as a Category 2 hurricane with maximum sustained winds of 100 mph, according to the 10 p.m. forecast of the National Hurricane Center. On this path, Isaac would arrive at the mouth of the Mississippi River on Tuesday at 7 p.m, and slowly move northwest, reaching a point on the north-central edge of Lake Pontchartrain at 7 p.m., with sustained winds of 80 mph.

National Hurricane CenterNew forecast shows Isaac cutting across New Orleans area as Category 2 hurricane

Center forecasters warned, however, that there's still significant uncertainty in Isaac's ultimate landfall that will likely remain until the storm becomes better organized and the steering effects of a high pressure system building west from the Atlantic Ocean become more clear.

The forecasters said a number of computer models used to predict Isaac's path have diverged in identifying its landfall, and the present forecast again nudges it towards those predicting a stronger turn to the west. But further changes in the forecast could occur on Monday.

The forecast path places much of the New Orleans area in the eastern quadrant of the hurricane as it crosses the area, meaning the effects of storm surge also are likely to be moved westward into the New Orleans area. The center's forecast calls for that surge to be between 6 and 12 feet. The more westerly track also increases the chance that surge could have more impact on West Bank communities such as the Lafitte area and portions of Lafourche and Terrebonne parishes.

"Hurricane force winds are expected to last many hours," said a 10 p.m. update from the Slidell office of the National Weather Service. On its present path, maximum winds are forecast at 65 to 80 mph, with gusts to 105 mph, and storm surge will result in worst-case flood inundation of 6 to 9 feet above ground level in low-lying areas and outside hurricane levees. The storm is likely to bring average rainfall of 8 to 12 inches, with isolated locations approaching 20 inches. The forecast also warned that Isaac could spawn isolated tornadoes as it approaches the coast and moves inland.

The new forecast also makes it clear that much of the New Orleans area will see winds of 60 to 100 mph, with gusts to 120 mph.

State Department of Transportation and Development workers were preparing Interstate 10 for possible use of contraflow, where all lanes are used in one direction, in the event an evacuation is ordered on Monday. While some mandatory evacuations have been ordered in areas closer to the coast, including Plaquemines Parish, Grand Isle, Lafitte and St. Charles Parish, on Sunday night, New Orleans Mayor Mitch Landrieu has not called for evacuation, and Jefferson Parish President John Young has not recommended an evacuation of areas protected by the improved hurricane levee system.

NOAA GOES EAST SatelliteIsaac is moving away from Key West and toward New Orleans.

Despite the dire tenor of the forecast, at 10 p.m. the National Hurricane Center said Isaac remained disorganized with maximum sustained winds only near 65 mph. That's expected to change during the next 48 hours, as Isaac strengthens into a hurricane.

"Satellite imagery has shown an increase in the area of cold cloud tops near the center of Isaac," said Senior Hurricane Specialist Dan Brown in a forecast discussion message. "However, there has not been any significant change in organization in radar data from Key West this evening."

Brown said the storm still is expected to intensify, because of the warm water it will traverse in the Gulf, and an upper air pattern favoring strengthening.

"However, the lack of an inner core and a large wind field could continue to be impeding factors for significant strengthening in the short term," he said.

The storm remains large, with tropical storm-force winds extending out more than 200 miles.

Isaac has continued to slow, and now is moving at 14 mph to the west northwest, with a northwest turn and even slower movement expected during the next two days. At 10 p.m., it was 510 miles from the mouth of the Mississippi River.

South Florida Water Management DistrictComputer models still show a spread of possible landfalls along north Gulf Coast.

Brown said computer models continue to show a wide spread for their predictions of landfall, ranging from the Texas-Louisiana border on the west to the Alabama-Florida border on the east, which means there remains great uncertainty about the final track forecast.

"Throughout the period, it is important not to focus on the exact forecast track due to forecast uncertainties and the fact that significant hazards extend well away from the center," he said.

and.....

http://enenews.com/all-of-assumption-parish-called-on-to-evacuate-ahead-of-storm-state-working-to-secure-sinkhole-equipment

Title: State of emergency
Source: The Advocate
Author: Robert Stewart
Date: Aug 27, 2012

[...]

The parishes Jindal called on to evacuate are: Ascension, Assumption, Jefferson, Lafourche, Livingston, Plaquemines, Orleans, St. Bernard, St. Charles, St. James, St. John, St. Tammany, Tangipahoa, Terrebonne and Washington.

[...]

[Louisiana Governor Bobby] Jindal said he expects he will have to declare mandatory evacuations for the parishes after state officials meet again Monday morning.

State government offices in those 15 parishes will be closed Monday, the state Division of Administration said in a news release.

[...]

Jindal said the state Department of Natural Resources is working with Texas Brine Co. LLC of Houston to make sure equipment at the site and surrounding areas of a massive sinkhole in Assumption Parish are secure.

[...]

Catharsis Ours

Monday, August 27, 2012

Tropical Storm Isaac update - Monday August 27th .... tracking suggest Louisiana as landfall ( west of New Orleans ) ..... the good news is at the present , it looks like we just may have a Cat 1 hurricane , which is a good development

Isaac Stubbornly Refuses To Become A Hurricane

HRRR Model Fields - Experimental - Tuesday morning 11:00 Central time

Maximum 1-minute Wind Speed Probability Table

Isaac forecast to hit New Orleans as Category 2 hurricane Wednesday morning, but models still uncertain

Published: Sunday, August 26, 2012, 11:00 PM Updated: Sunday, August 26, 2012, 11:25 PM

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