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 Levi32:


I believe he's referring to that which you were posting about...lol.
You got it Levi. I have my little list and neither of you are on it.
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431. DestinJeff 5:11 PM GMT on August 24, 2010

Based on what?

The agencies said an above-average season; nowhere in there forecasts do they say we should have 8 or 9 storms by now just because they forecasted an above-average season

Lets save the bashing of the forecasters until after the season is over; you know when we have the full set of storms so we can compare their numbers to the actual

To do it in any way on August 24th doesn't make sense
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I wonder what the 2pm outlook has for us. I wonder if the disturbance off of Africa is a depression yet? could be interesting.
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Link

Hurricane101, this shows that 96L is looking better and better. Also shows the other waves within the wave train or the AEWs.

StormW, is a well respected, well educated man when it comes to weather forecasting. It doesn't mean people can't disagree with him, just do it politely and back up your statements with some evidence on why you think that way and not because your gut says so. Pattern is becoming increasingly favorable for 96L to miss the break in the A/B and East Coast Highs and will head westward perhaps skirting the Lesser NE most Antilles islands. Right now though it is best to not get overly concerned given that the percentages are not very high that 96L makes it all the way across the Atlantic. 96L should become a TD by this evening and TS Earl by tomorrow morning given the very good appearance it has on satellite imagery and the rather moist canopy it is located in right now. Also wind shear is a moderate 10-20 knots and SSTs are near 27-28C so slow, gradual strengthening process looks to be underway. I think this system threatens the US east coast and percentages are placed at 30% do to continuity and modeled pattern change as a ridge of high pressure at 500mb noses and strengthens northeastward from the OV. As well as the A/B high building southwestward with time.

Danielle has become weaker in time do to dry air and modest wind shear affecting the core of the system as well as outflow restricted as well as CDO convective development on the western side of the circulation. The COC has become exposed and further weakening is possible the next 6-12 hours. Also conditions are expected to become more favorable for development thereafter so slow but steady strengthening is possible after the immediate weakening for the next 12 hours as she mixes out the dry air and shakes off the wind shear from the WNW. She has time to strengthen and appears to remain a non threat to Bermuda at this time. Will monitor progress of this storm and will mention of the possibilities of any landfall when needed.
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12z GFS shifted west towards Bermuda....they should still be watching very closely.

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440. IKE
Quoting DestinJeff:


You sound like that JFLORIDA dude. The season is a bust "idea" is based on the real-time correlation of date to storms.

Based on pre-season expectations ... this 2010 has, thus far, been a Bust. 4 on Aug 24 is incongruent with expectations.

As conditions change -- namely, some storms develop -- then perhaps teh season can begin to recover some of its lost expectation.


Hmmm....could it be? Nah...no way?
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Quoting Levi32:
Heck....12z NOGAPS has Danielle getting caught under the ridge...



This was that scenario I said would be a LOW, under 10% chance, still possible.
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Quoting Levi32:


I believe he's referring to that which you were posting about...lol.


oh ok lol, that was a bit confusing

but I dont consider Krycek a troll either; if I did I would not be responding to him
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437. IKE
Quoting IKE:
Danielle.....appears center at 17N and 47W.


The first advisory on Danielle, issued at 5pm EDT Saturday, the NHC had the 72hr coordinates at....

72HR VT 24/1800Z 17.5N 47.5W 85 KT

NHC is within 40 miles of where it is now....it's just moved a little faster.

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Quoting Levi32:


Nice!



Beautiful! Thank you!
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Quoting Levi32:


I believe it is only a scheduled thing where they turn it on for a designated hour. I have not found it available in real-time.


Noticed it is from the most recently launched satellite which is still in the testing phase.
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Quoting Hurricanes101:
424. ShenValleyFlyFish 5:09 PM GMT on August 24, 2010

You must be joking lol

I dont think either one of us are trolls, we were just having a discussion


I believe he's referring to that which you were posting about...lol.
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Heck....12z NOGAPS has Danielle getting caught under the ridge...

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424. ShenValleyFlyFish 5:09 PM GMT on August 24, 2010

You must be joking lol

I dont think either one of us are trolls, we were just having a discussion
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Quoting MississippiBoy2:
no matter what type of degree or etc.,mother nature is in control.

Btw,Storm and all the rest I still value your expertise,keep up the good work.
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I earned my 1st degree in being a man in the USMC...then a BSBM with a 3.76GPA at Oklahoma...and then...A Masters and PhD in Awesome Big Sexy Environmentalist Redneck Pseudo-Hipness from Floodman...point is am I the same?...no. No matter where you are planted, you will grow...so those extra years of study...yeah, they have a formative impact. Oh and check the pay stubs, there will be a difference there as well.
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I've gotta say, all of the arguing about whether or not a PhD is importance is making me want to be sick on my keyboard. I'm a scientist from the biological sciences, and frankly have heard this argument a ton in my field as well. The fact of the matter is that sure, the PhD provides ample opportunity for structured learning and testing yourself in a very challenging endeavor, but it is not the guarantee of a successful scientific career, nor is it the guarantee that someone is a brilliant scientist. I've known plenty of non-PhDs that can't hold their own against some brilliant folks without an advanced degree. Sure, book smarts and understanding how to think like a scientist is huge, but not everyone needs to go to school to have those qualities, and some that do get an advanced degree may not have the common sense to apply their education in the real world. Why are people looking at this as being a concrete argument? There is alot of gray here, and frankly with interesting stuff percolating in the Atlantic who cares?
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415. Krycek1984 5:06 PM GMT on August 24, 2010

The ULLs have been well documented by everyone who feels the season will be active, but in all honesty this season has had several systems very close to get a name, but just fell short. TD 2 was very close to being a TS before it made landfall in Mexico; we have also had 4 invests that had TS force winds but were never designated because they fell just short of what the NHC felt was necessary for classification

So if those 5 systems are named, and we are up to 9 storms; is anyone questioning how slow the season is? I would think the answer is no, but really it does not matter.

With 4 named storms, 2 depressions and several strong invests, there has been plenty to track this season

2009 repeat? Hardly
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423. JRRP
12z NGP... 120 hrs
Link
watch out Bermuda !
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Quoting nrtiwlnvragn:


That is an awesome loop. is it available in real time?


I believe it is only a scheduled thing where they turn it on for a designated hour for research purposes. I have not found it available in real-time.
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Hey Storm
All those who are questioning you are the first one that are always asking for your next update with the hope of actually understanding what is going on. Just continue doing what you do and don't worry about it. There are quite a few of us that look up to you and really appreciate what you do here on this blog.
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Quoting teammc:
StormW, why is everybody after you today. I for one think are one of the best forecasters, I have ever seen. You have alot of questions on your blog today.




I like Storm W. Too. He does add a lot to this forum. For the past few days people have been bickering about this and that. Hello, we have a cat. 1 storm in the atlatic and another that is following behind. Someone mentioned a disturbance off the coast of the East Coast! now can we all get back to the tropics, please.
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no matter what type of degree or etc.,mother nature is in control.
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So the conditions in the Caribbean (wind shear, MJO, etc.) still too unfavorable to worry about "blobs" in that area, right? Storm? Anyone?
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Quoting Buzzit:
I have been a longtime lurker on this board and only got around to registering a couple of days ago. I am based in the UK and closely follow the Atlantic Hurricane Season and then swap over to the Europe winter..

There are a number of people on this blog who provide a real service to people like me who wish to learn and understand the fascinating world of meteorology ! (and pass it on to friends)

I lament many of the new services like twitter because it only reinforces the soundbite and sensationalism that many people seem to think equals news or intelligent debate - very sad indeed.. You see the result of this in ever increasing amounts on this board and in real life

It would be great if there was an ability to see a list of all users that anyone has chosen to ignore during the last week / month and the quantity of people who have chosen to ignore them in total - and then be able to integrate that into your own ignore list.

In any case I hope to be posting relevant information to this board soon

Kind regards
Buzzit



Thank you, Buzzit. I look forward to good feedback from all members.
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Quoting Hurricanes101:
395. Krycek1984 4:58 PM GMT on August 24, 2010

I agree with most of your statement, but I ask you this

If it is ok for those who feel this season will be a bust to question all the agencies that forecasted an above-average season; then why is it not ok to disagree with the NHC?

Seems to me the same folks who question the agencies are the same ones that bash people for questioning the NHC

hypocritical much?


I really couldn't care less who does or doesn't question the NHC, or why or why they don't question the NHC.

It's pointless bickering. All I am saying is if you are going to wear the crown of being "scientific" than make sure you are truly being scientific...I see these prognostications for a very active storm season...which I agree with...but I don't see any addendums or paragraphs at the end stating what, if any, limiting factors are in place this season.
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Quoting StormW:


And mine aren't? Because, a lot of people see "degree" or Ph.D, and right away, that's the law of the land, and heaven forbid of you disagree, or even sometimes, out perform them. And that's garbage.

1 StormW, plus I've always heard " a handful of commonsense is worth an armful of learning", also " experience is the greatest of all schools so that even the fools will learn" just my .02cents
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413. IKE
Danielle.....appears center at 17N and 47W.
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Quoting Hokie76:
GOES-15 Super Rapid Scan visible image of Danielle Link


That is an awesome loop. is it available in real time?
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Quoting Levi32:


Bingo....


and before he says it works both ways, it does not

we do not bash those who feel this season is a bust, we just constantly ask them to backup their reasoning; something they have yet to do.
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Quoting Levi32:
Tropical Tidbit for Tuesday, August 24th, with Video


Thanks Levi...great work as always.

v/r

Jon
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Quoting StormW:


And mine aren't? Because, a lot of people see "degree" or Ph.D, and right away, that's the law of the land, and heaven forbid of you disagree, or even sometimes, out perform them. And that's garbage.


Storm, just ignore that crap...
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Quoting Hokie76:
GOES-15 Super Rapid Scan visible image of Danielle Link


Nice!
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I have been a longtime lurker on this board and only got around to registering a couple of days ago. I am based in the UK and closely follow the Atlantic Hurricane Season and then swap over to the Europe winter..

There are a number of people on this blog who provide a real service to people like me who wish to learn and understand the fascinating world of meteorology ! (and pass it on to friends)

I lament many of the new services like twitter because it only reinforces the soundbite and sensationalism that many people seem to think equals news or intelligent debate - very sad indeed.. You see the result of this in ever increasing amounts on this board and in real life

It would be great if there was an ability to see a list of all users that anyone has chosen to ignore during the last week / month and the quantity of people who have chosen to ignore them in total - and then be able to integrate that into your own ignore list.

In any case I hope to be posting relevant information to this board soon

Kind regards
Buzzit
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Quoting Hurricanes101:
395. Krycek1984 4:58 PM GMT on August 24, 2010

I agree with most of your statement, but I ask you this

If it is ok for those who feel this season will be a bust to question all the agencies that forecasted an above-average season; then why is it not ok to disagree with the NHC?

Seems to me the same folks who question the agencies are the same ones that bash people for questioning the NHC

hypocritical much?


Bingo....
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402. Relix
Senseless bickering from some envious posters notwithstanding...

I see the Northern Antilles safe from any system for the next 10 days or so. Earl should miss is, Danielle will definitely miss us. The next wave off Africa could probably recurve as well. A more westward steering should be set by then but seeing some of the models they are predicting an awkward flow 144 hours out.
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395. Krycek1984 4:58 PM GMT on August 24, 2010

I agree with most of your statement, but I ask you this

If it is ok for those who feel this season will be a bust to question all the agencies that forecasted an above-average season; then why is it not ok to disagree with the NHC?

Seems to me the same folks who question the agencies are the same ones that bash people for questioning the NHC

hypocritical much?
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400. Relix
Senseless bickering from some envious posters notwithstanding...

I see the Northern Antilles safe from any system for the next 10 days or so. Earl should miss is, Danielle will definitely miss us. The next wave off Africa could probably recurve as well. A more westward steering should be set by then but seeing some of the models they are predicting an awkward flow 144 hours out.
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399. Skyepony (Mod)
Quoting nrtiwlnvragn:


I was somewhat suprised the UKMET Office called for tropical development off the east coast. Last I looked at some cyclone phase did not show that. Guess it is possible.

NEW TROPICAL STORM FORECAST TO DEVELOP AFTER 12 HOURS
FORECAST POSITION AT T+ 12 : 34.5N 74.9W


That ULL over NC/VA is kinda close to there. Lotta dry air too. But yeah slim chance, there & the GOM.
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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.

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