To coin the cliché "A year and a day"

By: sullivanweather , 3:15 PM GMT on August 21, 2012

Current watches, warnings and advisories.

Eastern US current watches/warnings
Current watches, warning and advisories issued by the National Weather Service. Courtesy of NOAA.


Tropical Update

Barring the unlikely rapid development of 95L in the western Gulf of Mexico, Tropical Depression Nine in the central Atlantic will be upgraded to Tropical Storm Isaac later today (and will be referred as such throughout this blog). Every so often, a tropical wave moves off Africa and perks the interest of every and any observer of weather near or far. It screams out, "You better watch me closely," as if we didn't already notice its presence; a large, well-defined circulation accompanied with strong convection moving off the coast of Africa. Model guidance need not apply to aid in the forecast of the development of the particular wave into a tropical cyclone because there's that certainty that's there - this one is going to develop. And it isn't just that. Our weird sixth sense kicks in and infers to us this isn't going to be the typical storm but something much worse.

Tropical Depression Nine, in its entirety, is currently displaying a stunning satellite presentation for being just a tropical depression. The center of circulation is displaced slightly to the west of the massive overall circulation envelope almost 800 miles in diameter, covering a huge region of the central Atlantic Ocean basin. Several banding features are becoming well-defined as the storm breaks away from the ITCZ. In addition to the impressive presentation of the depression itself, a large arc of Saharan dust extends for some 2,500 miles from the northwest of the storm and trailing off into the eastern Atlantic, distinctly showing the extremely large amplitude of the wave spawning Isaac.

Tropical Depression Nine visible satellite image 12:15UTC. Courtesy NOAA

The forecast for Isaac is quite foreboding, as it should begin to make its first presence felt over the Leeward Islands in about 24 hours as a strengthening tropical storm. The official NHC forecast from then takes the storm over the northern Caribbean Sea where it will strengthen to a hurricane, skirting to the south of Puerto Rico and Hispaniola, then taking a turn toward the northwest in the general direction of the Florida Straits by early next week. On this track Isaac would affect all of the Greater Antilles with tropical storm conditions at the very least and be on track to affect the US mainland next week. However, for reasons I will explain, my reasoning is Isaac will move north of the HNC projected path and set a course for a potential historical impact along the East Coast of the United States.

Official NHC track for Tropical Depression Nine as of 8/21 8AM EDT.

The big picture is always important to take note of when forecasting tropical cyclones. A trough ten-thousand miles away over eastern Russia might become what ultimately determines the fate of a tropical cyclone in the Atlantic so it's very important to identify all potential features which may interact with the storm. As it currently stands, the strong +590dm 500mb ridge anchored over the Sargasso Sea driving Isaac west will begin to build toward the northeast in response to the deep trough slowly progressing eastward over the eastern United States. Several shortwave disturbances are clearly defined within the overall trough, aiding in the maintenance of such a deep August trough. Also of note is a broad southwest-northeast oriented tropical upper-tropospheric trough (TUTT), the base of which is centered around 75°W over Cuba. The erosion/displacement of the center of the 500mb ridge to the north and east combined with southwesterly upper flow emanating from the TUTT should allow Isaac to add a more northerly component to its track starting later today as it approaches the Leeward Islands.

As Isaac moves through the northeastern Caribbean Sea Wednesday evening into the day on Thursday toward the general direction of Hispaniola the TUTT to the west of Isaac will yield little ground and reorient itself on more of a north-south axis. This feature greatly factors in my belief of this storm gaining latitude as the expected more-vertical storm will feel greater effects from the developing mid/upper southerly flow over the central Caribbean.

0600UTC GFS depicting lingering TUTT over the western Caribbean, inducing southerly upper flow over the central Caribbean Wednesday evening.

One of the first effects Isaac will feel of the stagnant upper pattern ahead of the storm will be a slowing of the forward speed. This will allow for Isaac to be more easily influenced to the upper-level steering patterns, which should pull the storm northward. Additionally, due to the aforementioned large circulation of the storm, should the storm move into Hispaniola most of the storms angular momentum will lie on the Atlantic side of the island by that time, possibly allowing for the center to 'jump' north of Hispaniola and into the Atlantic basin. With this expected interaction with the terrain of Hispaniola Isaac may emerge as a large, disorganized minimal tropical storm but with plenty of warm water and a favorable upper environment Isaac should quickly take advantage and reorganize.

Friday afternoon through the weekend will be the time period in which Isaac will begin garnering the attention of the national media. It will be during this time frame in which Isaac will strengthen into a large formidable hurricane as it tracks west-northwest to northwest through The Bahamas around 10-12kts. The deep trough, doing its part of lift Isaac north, will be in the process of lifting out to be replaced by a transient ridge riding rather far to the north over southeastern Canada and northern New England to open next week. This should keep Isaac on a path that will bring it very close to the Carolinas by Tuesday. One saving grace might be due to the transient nature of the ridge quickly moving through westerlies to be replaced by a broad through over the eastern US by the middle of next week. This may act to recurve Isaac out to sea quickly, unlike Irene from last year which churned slowly up the entire stretch of the East Coast, dumping copious amounts of rain. The irony of this potential East Coast storm to last year's Irene is freakish. Both will be the "I" storm moving up the East Coast almost exactly a year apart (a year and a day to be precise). Just like the huge circulation Irene sported last year, Isaac is expected to be equally as large. This carries with it all the same issued Irene presented last year - a greater potential for coastal storm surge, a greater potential for inland flooding and the potential Isaac may not pack the expected punch in the wind department. Although the potential wind impact will ultimately be determined by the inner structure of the storm which is practically impossible to forecast just a few hours hence, let alone a week in the future.

This is just my preliminary forecast reasoning based on what I'm "seeing" might be potential important factors later on down the line at this very early stage. I will be here to track this storm and the one following it, currently developing southwest of the Cape Verde Islands. This, too, has the potential to become another storm to watch next weekend into the following week but should pose more of the threat to Bermuda and Atlantic Canada.


Radar: Northeast Region Loop

NE radar
Radar loop of the Northeast region. Courtesy of Weather Underground.


Northeast SST's
Sea-surface temperatures off the Northeast Coast. Courtesy of NOAA.

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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36. TheShovler3
2:53 PM GMT on September 06, 2012
My garden at my house is 18x20 feet, at my parents is 30x50 and i'm putting in a new one for next year i think 64x80 for just melons and pumpkins as they just overwhelmed a lot of things even with just a few plants where ever they rerooted in the soil they went nuts. I tried to tame them by cutting them back but i had no luck! We had a lot of rain over night tues-wed but it didn't do a whole lot for how far behind we are on the rain. We really need about a weeks straight of steady rain before fall.
Member Since: December 31, 1969 Posts: Comments:
35. listenerVT
4:21 PM GMT on September 05, 2012
We got 3" of rain here last night! It's a good thing, too, as it will quell any leftovers from the fire atop Mount Mansfield, for which 14 fire crews had to carry water in on their backs!

Check this out (be sure to read the embedded original story)... d-wildfire-extinguished
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34. listenerVT
5:45 AM GMT on September 05, 2012
Shovler, that's amazing!! How large is your garden?

We are having such loud, heavy rain I can't sleep! Radar shows red!
I keep thinking of that line from Rainy Night in Georgia:
"I feel it's raining all over the world."

Wish I could send some to the areas in drought!
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33. TheShovler3
3:54 AM GMT on September 05, 2012
Garden was great this year had some setbacks because of two hail storms but all in all a great year picked 30-40 cukes a day for about 2 months made relish and lots and lots of pickles. Lots of zuchinni and white patty pans, watermelons were pretty decent and I finally figured out how to tell when they're ripe. Cantaloupe were pretty good but not very sweet. Pumpkins are going crazy and tomatoes are just getting to peak harvest. Great year overall!
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32. originalLT
7:00 PM GMT on September 04, 2012
Hi Sully, hope you are OK and checking your blog from time to time. Like to get your feelings on Leslie, and the active period coming up with tropical systems, that is projected by the GFS and other models. Thanks. LT
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31. libertygirl
10:03 AM GMT on September 03, 2012
Oh YAY! Sully you're are back?! Thank the snowy heavens above! I am back in Liberty for the long haul. I am so happy to be back up here and more so, to see you back at the underground. I look forward to winter snow reports! Welcome back. :))
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30. listenerVT
1:59 PM GMT on September 02, 2012
It was chilly here this morning!
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29. listenerVT
1:59 PM GMT on September 02, 2012
Quoting TheShovler3:
oh man! you're back fantastic news!!!! hope all is well and i look forward to the fall and winter months. have you had a chance to put into a garden this year?

Hiya Shovler!
How's your own garden? We got a late start here and are just about to finally have tomatoes. Mostly, we're putting in a new fence, so have flower gardens to move and replant.
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28. TheShovler3
1:56 PM GMT on August 29, 2012
oh man! you're back fantastic news!!!! hope all is well and i look forward to the fall and winter months. have you had a chance to put into a garden this year?
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27. listenerVT
2:23 AM GMT on August 29, 2012
Ahm heer awl bah mahseff. :-(
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26. listenerVT
6:39 AM GMT on August 28, 2012
Any chance that's a complete eyewall I see?
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25. listenerVT
3:00 AM GMT on August 28, 2012
Quoting jerseycityjoan:
Can't be believe that this might end up hitting New Orleans and surrounding area. Also that it's speed is expected to slow down around landfall, so it will linger and dump rain for hours.

And just in time for the anniversary of Katrina, too. :-(
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24. jerseycityjoan
10:59 PM GMT on August 27, 2012
Can't be believe that this might end up hitting New Orleans and surrounding area. Also that it's speed is expected to slow down around landfall, so it will linger and dump rain for hours.

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23. listenerVT
5:31 PM GMT on August 27, 2012
How do folks Imagine Isaac will affect weather once it makes it's way to the middle of the country?
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22. crowe1
2:14 PM GMT on August 26, 2012
Holy cow, great to see you back Sully!
I've been absent for a bit too, lurking I guess.
Anyway, the biggest weather news around these parts is, of course, no rain. Mature trees are starting to brown and drop leaves already! We also had a rotating storm pass overhead about 2 weeks a go that produced gusts of 66 mph!
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21. listenerVT
1:40 AM GMT on August 26, 2012
Yesterday the Republicans were telling convention goers not to worry because Isaac will pass a hundred miles or more out at sea. Today they decided to postpone the convention by a day. I guess they finally looked at the satellite map! :-)

BTW, Sully, I notice that Isaac has emerged on the north side of Cuba, as you predicted!
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20. listenerVT
3:57 AM GMT on August 25, 2012
Ah, Sully, thanks for the comfortable words!

18' above flood stage is hard to wrap your mind around! How often has the Delaware flooded? I think the hardest part about the devastation in Vermont is that it was unprecedented in many of the areas it hit. There was one hillside we came upon that had large stones all down it, where obviously the rushing waters had flowed. And at the bottom was a broken sugar house, with a sign saying "We lost everything but plan to rebuild. Donations appreciated." And here it was a year later with no sign of rebuilding under way. You don't expect a small mountain to turn into a river, crash into your sugar house and carry away your house!

I hope the folks down south get more drought relief than destruction!

And thanks again for being here...especially this week. ♥
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19. sullivanweather
2:11 AM GMT on August 25, 2012
Good evening, Listener!

I think we are in the clear here in the Northeast for this storm. The flow across the northern tier of the country is going to be too zonal to allow Isaac to penetrate any further north than the Mason-Dixon line.

It is now obvious Isaac won't be moving into the Dominican side of Hispaniola, so center reformation to the north of the island won't be happening; this storm will maintain its original center. Isaac should now take a line about 100-150 miles west as a result so that takes the storm path through eastern Cuba and through the southernmost Bahamas. On this path, even though it goes through land, the land Isaac travels over are the thinner peninsulas where some portion of the center might remain over water so Isaac won't be weakening much and I think once it clears Cuba it should become a hurricane within 12-18 hours.

From there it's on to southeast Florida, around Miami, for what's looking like a cat2 strike. Plus that little high pressure area moving by to the north should bend Isaac back west-northwest. Comes off the coast around Punta Gorda as a strong tropical storm or minimal cat 1 cane and should grow back into a cat 2 before bending back to the north and hitting between Biloxi and Pensacola. It'll be a bad storm down there but it won't be a devastating storm. It'll recurve after that and move off the coast around North Carolina and head on off, caught in the westerlies. If anything, it should help to eliminate the remaining drought areas in the Southeast.

We took a rafting trip down the Delaware River yesterday and in some spots along the shore you can spot evidence of the flooding from prior years that's just amazing. You'll be standing on a rock ledge about 4' above the river stage and there's a large tree 10' above you with straw, branches, other tree trunks, etc. all wedged in where the limbs split off the trunk. That's like 17-18' above the current stage.
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18. listenerVT
12:16 AM GMT on August 25, 2012
I'm so grateful, Sully, for this blog this week, as Vermont prepares to face the anniversary of Irene's devastation. Last Sunday we drove down to the Weston Playhouse to see Fiddler on the Roof (excellent). It was a sobering drive, seeing how many areas had been washed out and rebuilt, and how many spots are still a still looking disheveled (even moved) and we wondered what's become of those people. We also stood out back of the Playhouse where the stream had become a rushing, mangling river torrent and marveled at how much they've recovered.

So I'd be grateful if Isaac would please not come up the coast. The people here are still too traumatised. I'm watching Isaac's progress closely. Since it's not out of the question that Isaac could reach Cat 2 or 3 status, what do you think might occur should Isaac enter the GOM and intensify? Would it have sufficient thrust to cross land, push past the trough, and come north? Given the intensity of the wave that formed Isaac, I think intensification after Cuba could be impressive.

And that freaks me out a little bit.
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17. NEwxguy
3:25 PM GMT on August 24, 2012
The wave train in in full swing right now,but the Atlantic just is not going to let them make it across the Atlantic.Joyce got ripped apart and 97L will probably die the same death.

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16. listenerVT
2:32 PM GMT on August 24, 2012

I'm on the run this morning, but will come by later today!!!

Utterly heartglad!!! ♥
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15. sullivanweather
2:21 AM GMT on August 24, 2012

Hey! How ya been?

Yeah, lots of new faces here. And new faces usually mean a younger, inexperienced and impressionable crowd. The wild swings start; the center's here, no it's here. It gets down to over-analyzing every latest image of a satellite loop, the different IR channels, which is crazy for a storm like this. These storms, which are huge and slow to get going, it's best to simplify, and pinpoint the macro-pattern. It's like forecasting a huge broad trough during the wintertime as opposed to a shortwave within the trough. The broad trough is much easier to forecast in terms of trough amplitude and axis instead of trying to nail down the position of a fast-moving shortwave and whether it not it's close enough to the coast to spin up a nor'easter. Isaac spawned from a tropical wave with one of the largest amplitudes I've ever seen from a AEW. Although a tropical cyclone within a wave is akin to a shortwave within a trough, knowing the nature of the tropical wave - it's amplitude, amount of SAL, etc., hints at the constraints of what's possible.
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14. NEwxguy
2:31 PM GMT on August 23, 2012
Great to have you back,was just in the main blog and random stuff is being thrown at the wall as if they are facts and saw you come in with a well thought out analysis with an explanation of your thoughts which blew away anything the others in there had to say.
Look forward to you thoughts as Isaac moves up.
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13. jerseycityjoan
2:22 AM GMT on August 23, 2012
I really hate to see poor, miserable Haiti under the gun again.

They need something like a 20-year or 50-year tropical storm moratorium, which of course they will not get.
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12. jerseycityjoan
4:05 PM GMT on August 22, 2012
Very glad to see you back. Hope you've been well since we last heard from you.

I recall this blog was very useful last year when Irene came along.

It's reassuring to know you'll be around this year too.

Take care and thanks for all your efforts.

Member Since: December 31, 1969 Posts: Comments:
11. originalLT
2:55 PM GMT on August 22, 2012
Thanks for the answer Sully. I am good, and at the end of this past June, into early july, my wife and I went on a trip to SE Alaska! It was incredible. Thought of you alot, I know it would be great if you could do that some day. (I'm 63, so it's taken me a long time to get to make this trip.) Our "launch point" was Seattle, and the flora there was tremendous, so beautiful. As to a hurricane coming up the coast, I see your point for this year, with the water temps so high. But I still maintain it would have to be moving pretty fast to maintain at least Cat2 status--not a slow pace like Irean of last year, because I think a "Slower Mover" will entrane continental air into it and start to weaken it. Anyway, again thanks.
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10. shoreacres
12:58 PM GMT on August 22, 2012
Good morning, Sully! Sure is good to see you, and to get your take on Isaac. I looked at the ecmwf this morning and got even more creeped out. I keep wondering if this storm named Isaac is going to turn into another "Isaac's Storm" and head over to Galveston for a replay of 1900. We'll certainly hope that's nothing more than my over-heated imagination!
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9. sullivanweather
12:36 PM GMT on August 22, 2012
Where you live, or course. =)

If you want to know when, I'm guessing winter really arrives the second week of December this year so start getting your hopes up after Thanksgiving, just 13 short weeks away.

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8. HeavySnow
12:10 PM GMT on August 22, 2012
Holy cow it's Sully! Where's my next snowstorm?
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7. sullivanweather
10:59 AM GMT on August 22, 2012
Good morning, Numberwise!

How's things been up your way?
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6. sullivanweather
10:55 AM GMT on August 22, 2012
Hey, LT! How ya been?

I think Isaac running though the length of Hispaniola and a portion of Cuba is a possibility. Hurricane Georges did that and unbelievably remained a hurricane the entire time. But that was a mature storm. Isaac is just getting its act together so the land interaction will be much more detrimental to development. However, as I hinted at in the discussion, due to how large the overall circulation of Isaac is should it come through Hispaniola and become disrupted the center of the vortex within the overall circulation could easily jump to the north side of the island. The overall circulation is huge but for a time yesterday afternoon the actual vortex center was exposed and void of convection. That vortex is still quite small, especially so in comparison to the overall system. This gives me the impression that center reformation has a greater than normal possibility if it should run into those high mountains on Hispaniola and I'm pretty confident the storm is heading in that direction.

As far as the storm's impact up the coast I don't think it would weaken as much as one would expect.

Check out the 25°C isotherm, it goes right up to New York City. That should easily be able to maintain the strength of Isaac up to 40°N with everything else remaining equal. There's 20°C+ waters in the Gulf of St.Lawrence and the ocean temps around Atlantic Canada is running 3-5°C above normal. This is absurdly high and it is these areas which produce stable, stratified maritime air over those colder ocean waters which chokes off instability of tropical cyclones and weakens them. With that influence much lessened due to how warm those SST's are there won't be as much stable air drawn into the storm north of 40°N as well.
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5. goofyrider
8:50 PM GMT on August 21, 2012
Hey Chief nice
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4. LettyS
6:13 PM GMT on August 21, 2012
Seeing this blog entry just made my day!

Will be following Isaac's development with great interest, and looking forward to you ushering us through it, Sully.

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3. NumberWise
4:31 PM GMT on August 21, 2012
Hello, hello! What a welcome surprise this blog is!
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2. originalLT
4:02 PM GMT on August 21, 2012
A couple of things on what should be Issac, could the vector of the storm have it run the entire gauntlet of Hispaniola and Cuba, there by really putting a "dent" in it?--really weaken and disrupt it. Also, just my thoughts on a Hurricane coming up the coast. I feel that if one should come up the coast, and still remain pretty powerful, like a Cat.2 even above 40 degree lat. , it would have to be moving North or NNE, pretty fast(like the 1938 storm, or even Donna of 1960,) otherwise if it moves relatively slowly, like Irean did last year, it will decay in the cooler waters(70'sF) And weaken because of land interaction. What do you feel about this? Thanks LT
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1. originalLT
3:49 PM GMT on August 21, 2012
"Love you Sully", welcome back! LT
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Thomas is an avid weather enthusiast, landscaper and organic gardener. This blog is dedicated to Northeast and tropical weather forecasting. Enjoy!

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