A Nightmare Scenario

By: Bryan Norcross , 3:07 AM GMT on August 27, 2012

What a horrendous confluence of events. Tropical storms never get on people's radar, and the fact that Isaac passed Key West with less effect than a gusty afternoon thunderstorm made the situation worse. Even with a Cat 1 hurricane, will people take action tomorrow that may save their life Tuesday night?

Isaac's extremely large circulation is one of the factors that should make it intensify relatively slowly, and a track that misses the high heat-content pools in the Gulf should help in that direction as well. Plus it has less than two days over the water before landfall. But, the water ahead is still plenty warm - over 85 degrees - and the atmospheric pattern looks very favorable for strengthening. Taken together, the NHC's Cat. 2 forecast looks reasonable, though preparations should be made for a Cat. 3, given the lack of skill inherent in intensity forecasting.

In any case, that same large circulation will move a lot more water toward the coast than an average hurricane. The entire Hurricane Warning area - from Louisiana to the western Panhandle - is extremely vulnerable to storm surge flooding. The NHC is forecasting 6 to 12 feet of water ABOVE THE GROUND in spots along that stretch of coast.

Normally, the exact amount of surge will be dependent on the exact track and where in the tide cycle the storm comes in. In Isaac's case, however, there will be such a long duration of onshore winds, due to the storm's size and slow forward speed, the water may stay high for more than one tide cycle.

In fact, that size and slow forward speed will make this a hurricane experience like none in memory, if it comes together as forecast. The weather will deteriorate tomorrow (Monday) in the Florida Panhandle, and tomorrow night across the rest of the northern Gulf coast. Then Tuesday the storm approaches the coast and a whole day later it is just inland on the current timetable. Even Thursday there is still onshore wind over part of the coast.

People will experience strong, howling winds and torrential rain for 24 to 36 hours or more in this scenario. They will be trapped at home, many without power.

And then there's New Orleans. The storm as currently forecast should NOT exceed the capabilities of the new super-strong levees, but what if the storm comes in stronger? What a decision to have to make! Should they call an evacuation or not? In addition, there are populated areas outside of the levee-protection system.

Tomorrow (Monday) will be a day for big decisions from Louisiana to the Florida Panhandle. With life-threatening storm surge expected well away from the landfall point, widespread evacuation orders are likely.

And then there's the inland flood threat from the torrential rain.

Unless something unexpected happens, it's truly a nightmare scenario.

Continuing coverage, of course, on The Weather Channel.

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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8. jerseycityjoan
8:38 AM GMT on August 27, 2012
Thanks for making the situation clearer.

Obviously we still don't know what will happen exactly but I didn't realize, for example, how long the storm would take to pass over the coast at landfall.

I hope the media gets the word out about how serious this storm may be and that people listen.
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7. thankssomuch
7:26 AM GMT on August 27, 2012
So glad that there is a weather person out there that is telling people what is really going to happen for the most. Now that this has hit the warm water its going to get jiggy with it and agree on the cat 3 possiblities.
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6. redagainPatti
5:19 AM GMT on August 27, 2012
I wonder if this storm is going to run the eye right over NO or worse yet... landfall just west of the city.... Been thinking this for a while... just have bad feelings about this storm.
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5. Grothar
4:46 AM GMT on August 27, 2012
Strange storm. Thanks for the updates. A lot of people don't know you are here yet. They don't want to miss your input. I can't wait for your opinion on the next system I see that may bring some system again near the Antilles.
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4. originalLT
4:35 AM GMT on August 27, 2012
Thanks for the new blog. Like you guys said on TWC., as soon as Isaac gets away from the influence of that ULL near the Yucatan, it probably start to intensify fairly rapidly--not RI.
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3. CosmicEvents
3:18 AM GMT on August 27, 2012
Thank you Bryan.
A nightmare scenario indeed.
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2. palmettobug53
3:17 AM GMT on August 27, 2012
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1. TheDewd
3:16 AM GMT on August 27, 2012
Thanks, and we all hope that people listen. Floyd in 1999 never even made landfall on the Outer Banks, but it sat off of the coast for three days and the surge and debris in the surf destroyed my grandparents' cottage in Nags Head. I fear the slow-movers more than any other kind.
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