Danielle a hurricane; TD 7 forming off coast of Africa

By: Dr. Jeff Masters , 2:18 PM GMT on August 24, 2010

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Hurricane Danielle has stopped intensifying and is now looking a bit ragged this morning, but remains a respectable Category 1 hurricane with 80 mph winds. The intensity of Danielle's heavy thunderstorms has waned in the past few hours, and the organization of the storm is less impressive. This is probably due do strong upper-level winds out of the west that are creating a moderate 10 - 20 knots of wind shear, and injecting some of the dry air from the Saharan Air Layer (SAL) that surrounds Danielle. Danielle is over warm 28°C water, but is far from any land areas.


Figure 1. Morning satellite image of Tropical Storm Danielle (left side of image) and the forming Tropical Depression Seven (right side of image.)

Forecast for Danielle
A powerful trough of low pressure over the mid-Atlantic Ocean will begin to pull Danielle more to the northwest by Wednesday, keeping Danielle well to the east of Bermuda. Most of the models predict that this trough will be strong enough to fully recurve Danielle out to sea. It is possible that Danielle could eventually threaten Newfoundland, Canada, but it currently does not appear that any other land areas will be at risk from this storm. History suggests that a storm in Danielle's current location has only a 20% chance of making landfall on the U.S. East Coast. If Danielle passes east of Bermuda, as forecast, these percentages drop to less than 5%. As far as intensity goes, it is looking unlikely that Danielle will attain major hurricane status (115+ mph winds.) There is enough dry air and wind shear affecting the storm today that it will take several days for the storm to recover its strength, making it less likely the storm can hit Category 3.

The formation of Danielle is remarkable in this it was successfully forecast by the GFS model nearly two weeks in advance. The ECMWF and NOGAPS models also did a good job of predicting Danielle's formation a week in advance. The models are getting better and better each year at forecasting genesis of tropical cyclones, though a successful 1-week forecast of genesis is still a rarity. For example, none of the models foresaw the development of 96L until just 3 - 4 days ago.


Figure 2. Plot showing historically the percent chance of a tropical cyclone in a given location impacting the U.S. East Coast. For storms in Danielle's current position (orange hurricane symbol), about 20% of them go on to hit the U.S. East Coast. For storms in 96L's current location (red circle with a "?" in it), the odds are also 20%. Image credit: Bob Hart, Florida State University.

96L (soon to be Tropical Depression Seven)
Satellite images suggests that a tropical wave (96L) that emerged off the coast of Africa yesterday morning has developed a closed circulation, low-level spiral bands, and an increasing amount of heavy thunderstorms. While this morning's ASCAT pass does not show a clear closed circulation, satellite estimates of 96L's strength support calling this a 30 mph tropical depression. It is likely that this storm will be designated Tropical Depression Seven later today. 96L is already bringing heavy rain and strong, gusty winds to the southern Cape Verde Islands. Winds were sustained at 26 mph at Mindelo in the northwest Cape Verde Islands this morning, and 24 mph at Praia, the station closest to the center of 96L. Both stations were reporting widespread dust, due to strong winds blowing Saharan dust from the coast of Africa. However, water vapor satellite images show that only a modest amount of dry air is accompanying this dust, and dry air is currently not a major detriment to 96L. Wind shear is about 10 - 20 knots, and sea surface temperatures are warm, 28°C.

Forecast for 96L/Tropical Depression Seven
Wind shear is predicted to remain low, 5 - 10 knots, for the next four days. SSTs will cool a bit to 27°C by Thursday, but this is still above the 26.5°C threshold for hurricane development. Dry air will probably be the main inhibiting factor for 96L. Most of the intensity forecast models bring 96L to hurricane strength by four days from now, and this is a reasonable forecast. 96L should become Tropical Storm Earl later today or on Wednesday, and will probably bring sustained winds of 40 mph to the southernmost Cape Verdes Islands tonight and Wednesday.

The long range fate of 96L remains unclear. The storm is being steering by the same ridge of high pressure steering Danielle, and will initially follow a track similar to Danielle. 96L may encounter the cold waters stirred up by Danielle at times this week, inhibiting development. As 96L approaches the central Atlantic five days from now, the storm will encounter the same mid-Atlantic trough that will be steering Danielle, and 96L should turn more to the northwest. It is unclear at this point whether this trough will be strong enough to fully recurve 96L out to sea, east of Bermuda. This will, in part, depend upon how strong Danielle gets. A stronger Danielle is likely to create more of a break in the ridge of high pressure steering 96L, encouraging the storm to turn north and recurve out to sea. A weaker Danielle will make 96L more likely to miss recurvature, and follow a track to the west or west-northwest towards the U.S. East Coast early next week. History suggests that a storm in 96L's current location has only a 20% chance of making landfall on the U.S. East Coast.

When will the Caribbean and Gulf of Mexico get active?
The large scale atmospheric circulation over the Caribbean and Gulf of Mexico currently features relatively dry, stable, sinking air. This is due, in part, to the Madden-Julian oscillation (MJO). The Madden-Julian oscillation is a pattern of enhanced rainfall that travels along the Equator from west to east. The pattern has a wet phase with large-scale rising air and enhanced thunderstorm activity, followed by a dry phase with large-scale sinking air and suppressed thunderstorm activity. Each cycle lasts approximately 30 - 60 days. When the Madden-Julian oscillation is in its wet phase over a hurricane-prone region, the chances for tropical storm activity are greatly increased. The latest MJO forecast from the GFS model calls for the wet phase of the MJO to move into the Caribbean during the first week of September. However, keep in mind that forecasts of MJO activity 1 - 2 weeks in advance are not very skillful. The GFS model forecast of MJO activity made two weeks ago did fairly well for the first week, but poorly for the second week of the forecast.

Tropical Storm Frank spares Mexico
Over in the Eastern Pacific, Tropical Storm Frank has moved away the coast far enough from the Mexican coast to no longer pose a heavy rainfall threat, and all tropical storm warnings have been dropped.

"Hurricane Haven" airing again this afternoon
Tune into another airing of my live Internet radio show, "Hurricane Haven", at 4pm EDT today. Listeners will be able to call in and ask questions. The call in number is 415-983-2634, or you can post a question in the comments area on my blog during the show. You can also email the questions to me today before the show: jmasters@wunderground.com. Be sure to include "Hurricane Haven question" in the subject line. I'll focus on Danielle, Earl, and Frank, and discuss the possibilities of a hyperactive Atlantic hurricane period coming during the first week of September.

Today's show will be 30 - 45 minutes, and you can tune in at http://www.wunderground.com/wxradio/wubroadcast.h tml. The show will be recorded and stored as a podcast.

Jeff Masters

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Quoting extreme236:


Somethings bound to tap into that at some point.
And when it does, it's going to be ugly.
Member Since: September 2, 2009 Posts: 130 Comments: 21091
never took my eyes off her just left the room and came back to find comp models updated and saw now we are possible targets
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I bet the NHC is going to discount the GFS in their next advisory, call it an anomaly. In all honesty we need the 0z runs to come out to see if this trend continues.
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1996. unf97
Quoting Levi32:


I'd say possible but not probable. While she make a run in that direction, I think ultimately she will recurve offshore. It's rather hard to say at this point whether she will make a run like the 18z GFS/NOGAPS, or recurve straight out east of Bermuda, but either way Bermuda should be on the lookout, as well as New England just in case, but I think it's more likely to recurve east of the US.


I agree with your rationale Levi. Although Bermuda really is going to get a close call with Danielle for sure.
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Quoting StormW:


I think what is happening is, if you back to your loop, the way it appears to be setting up, if you look on the east coast at the trof, and the ridge directly to its east, then look a little NE of there, which appears to be another ridge center, and the ridge near Danielle, you can pretty much see it setting up to "split" in the middle of that. That is supposed to be her "out". Just isn't happening very quick.


Yes sir i see that too....and your right it is slow to develop if it does....but, you can clearly see also how strong the High is just north of Puerto Rico as well.
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Quoting MiamiHurricanes09:
Ouch?



Somethings bound to tap into that at some point.
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Ouch?

Member Since: September 2, 2009 Posts: 130 Comments: 21091
Quoting StormW:


Thanks for that loop and your input BTW!


LMAO
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1989. Levi32
The big trough basically pushes the high that is currently northwest of Danielle off to the north of her (turning her slightly more west for a time), but once the high is pushed out of the way she will either recurve straight out or get trapped under the 2nd ridge for a time.
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Quoting Levi32:


The weakness currently along the Carolina coast yes, but a bigger trough is digging in behind over the northern US and that's the one that will recurve Danielle. That trough will break down the ridge to her northwest altogether.


Man I have a lot to learn lol!
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Quoting weathercrazy40:
ok what happened i left the comp for a litle only to come back and see big change in comp models so im taking it sitting here in south eastern mass just north of cape cod we now have to keep and eye on danielle


You should never have taken your eye off Danielle till the storm dissipates... and that is for everyone in the basin
Member Since: August 1, 2006 Posts: 28 Comments: 3716
Evening, all.

WELL! What a difference 12 hrs can make! It was very startling to see the TS symbol for Danielle on the NHC site just now. I guess there really WAS a dry slot after all.........

I'm really going to be watching this one now... I'm rather expecting MUCH more of a threat to the Bahamas, TC, FL than I did yesterday about this time.... Not saying it's going to hit, but a better chance of getting further west before it recurves seems more likely. I also not that Bermuda is smack dab in the middle of the cone....
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1983. Levi32
Quoting troy1993:
So Levi32 i know its not likely but is it possible that Danielle has a chance of going towards the Northeast coast because I hear that the ridge of high pressure is suppose build over the Northeast by the weekend.


I'd say possible but not probable. While she make a run in that direction, I think ultimately she will recurve offshore. It's rather hard to say at this point whether she will make a run like the 18z GFS/NOGAPS, or recurve straight out east of Bermuda, but either way Bermuda should be on the lookout, as well as New England just in case, but I think it's more likely to recurve east of the US.
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ok what happened i left the comp for a litle only to come back and see big change in comp models so im taking it sitting here in south eastern mass just north of cape cod we now have to keep and eye on danielle
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Next, or not? PGI36L isn't the impressive blob approaching the coast, but rather the mass over Nigeria/Benin, which doesn't appear to have much of a chance for development as it's too far south. Hmmm...

Click for larger image:
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Aqua/Terra satellite image of 96L from this morning.

Member Since: September 2, 2009 Posts: 130 Comments: 21091
Quoting StormW:


I basically see a stationary mid to upper trof, and a ridge to its east.


It appears to also that the Low has now stopped coming South and is now about to move to the North and ride up and over the Ridge in the trough. Will that cause the Trough to move out with the Low and cause high pressure to build in behind it before Danielle gets there?
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1977. Levi32
Quoting doorman79:
Another basic one lol! Isn't the two highs(one over midwest, and one to her nw) pushing the weakness north? Sorry trying to learn!


The weakness currently along the Carolina coast yes, but a bigger trough is digging in behind over the northern US and that's the one that will recurve Danielle. That trough will break down the ridge to her northwest altogether.
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So Levi32 i know its not likely but is it possible that Danielle has a chance of going towards the Northeast coast because I hear that the ridge of high pressure is suppose build over the Northeast by the weekend.
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1973. palmpt
Quoting srada:


I come on in the evening and Models are trending to the west now..even some west of bermuda? this aint looking too good for the conus


Fish!
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Another basic one lol! Isn't the two highs(one over midwest, and one to her nw) pushing the weakness north? Sorry trying to learn! (bad grammar sorry!!!)
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Just bloggin'..but looking at the longer ranges of the GFS, I wonder if were not seeing a hint of a Fujiwhara effect between Danielle and TD7...one that might shift either or both onto the coast beyond day-6.
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1970. Levi32
Quoting TampaSpin:
StormW and all Look at this loop and look at the Low on the East Coast and tell me what you see.....I DON'T LIKE IT!


Noreaster, nontropical.
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Quoting KEEPEROFTHEGATE:
06L/H/D/C1
MARK
18.13N/49.36W



Those are great animations...
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1968. unf97
Quoting extreme236:


Well thursday is 48 hours from now, hence the 90% chance within 48 hours lol


Yep. 96L I think will probably get upgraded to TD by this time tomorrow evening.
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1967. Levi32
Quoting GTcooliebai:

Hi Levi, I just took a look at the intensity models and in 5 days it has Danielle weaking & possibly just becoming a remnant low. Do you think that is the reason why some of the models have it going west towards the US East coast?


No, it wouldn't be dying if it headed towards the US east coast. In fact her strength may not have all that much to do with it....just the longwave pattern and whether the ridge is able to block her or not. She would likely be getting sheared a bit, but not to pieces. She would be a formidable storm.
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Quoting TampaSpin:
Looks like Dry Air and the ULL to Danielle's North will keep her from becoming a huge storm that i first thought.....given that...i don't believe she will now go much further West than models are showing....Just my Opinion.
just caught Cantore and Norcross on the weather channel (not on purpose was just flipping and they were on)...Brian just went over the new GFS run and showed why it has it scraping the NE CONUS, he says its the ULL to her north that will ultimately steer her that way (unfortunately the volume was down and I didn't here everything he was saying and my wife switched the channel so cant rewind the DVR...).
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Quoting StormW:


Well, technically...it's not...that's why the current stall, until the "weakness" strengthens.
just being funny, but how could weakness strengthen?
Member Since: August 5, 2007 Posts: 0 Comments: 679
Quoting Levi32:


Probably because of the model consensus slightly farther west, but they likely won't go towards the new GFS solution.

Hi Levi, I just took a look at the intensity models and in 5 days it has Danielle weaking & possibly just becoming a remnant low. Do you think that is the reason why some of the models have it going west towards the US East coast?
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Could anyone explain why there is dry air north of the Leeward Islands?
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1960. srada
Quoting jason2010xxxx:
three models jump to the west.


I come on in the evening and Models are trending to the west now..even some west of bermuda? this aint looking too good for the conus
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1959. Levi32
Quoting Hurricanes101:


I think TD 7 wont show up until Thursday, I feel the 90% is a bit too high right now


Well, it honestly has a better chance now and the next 48 hours than it has after that. By that time Danielle could be shearing it. If it overcomes the SAL and boosts up the convection it could quite easily get classified. 80-90% seems fine to me but we'll see.
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Quoting StormW:


Well, technically...it's not...that's why the current stall, until the "weakness" strengthens.


Thank you!
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Just sitting and watching the 2010 Parade Of Equatorial Waves:

Click for larger image:
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Quoting Levi32:
96L doesn't have a well-defined surface circulation yet, but it's getting there slowly.

Oops, didn't see the ASCAT pass, still has some minor work to do, likely will be a depression within the next 48 hours.
Member Since: September 2, 2009 Posts: 130 Comments: 21091
Quoting Hurricanes101:


I think TD 7 wont show up until Thursday, I feel the 90% is a bit too high right now


Well thursday is 48 hours from now, hence the 90% chance within 48 hours lol
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1953. tramp96
Quoting Levi32:


I could totally set him up to do it :)

That would be great. Watching your blog is a better learning experience than the written word.And with two blogs...well.
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1952. unf97
Good evening StormW
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1951. bappit
Danielle and Earl-to-be (?) from CIMSS MIMIC TPW. Last frames of gif animation.


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Quoting Levi32:
96L doesn't have a well-defined surface circulation yet, but it's getting there slowly.



I think TD 7 wont show up until Thursday, I feel the 90% is a bit too high right now
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Has anyone heard of who? If its somebody from the nhc its possible they are in a supporting role not a lead forecaster. Just saying...
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.