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 engine112:
So this will be my last post on the main blog page. I came home this morning after working 12hrs. in florida, in the rain, taking care of the sick and injured. I read up on the updates and posted three questions. I know I am not a meterologist but I like to learn things, so I ask questions. When I wake up later today I waded through 150 or more post only to find alot of people whinning and moaning. It's like recees time in the fourth grade on here. All I wanted was a few scientific minded responses and the blog is so over loaded with BS (that's not bachlor in science either) that I can't even see my original post---

This blog has lost its value to me.

Have a good day and remember, threat your neighbor the way you would want them to treat you! (some people may due well to remember this rule - remember the golden rule)


haha i think "threat your neighbor" is almost as funny as "we are doom" !
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Quoting Krycek1984:
I am just a naturally curious person that likes to "know". The existing parameters for an above-average season are already well known: La Nina conditions, high SST anomalies, lower-than average basin-wide shear, vigorous African lows, some overall pattern positives, etc.

But what are the negatives? The world is not black and white, it is in grey. I know we had a lot of ULL's this year. But why? That is the important question to me. I can see with my own eyes they were there. But the question to me once again is why? And what can we learn from that unexpected development, insofar as future forecasting goes?


Take two (blog ate take 1)

We do not fully understand tropical cyclogenesis yet, though we are getting better at it.

Forecasting mesoscale and smaller features, such as ULLs more than a few days out is still rather difficult (look at the praise given to GFS for forecasting Danielle 2 weeks out).

Now, we know some of the large scale features necessary for tropical cyclogenesis, and those are met this year. But perhaps we do not yet understand the large scale features that have lead to the persistent ULLs across the basin this season. So in the coming years people are likely to study this, and perhaps they will discover what has caused these negative features to be so prevalent in the early part of the season this year. This will, in turn, give us better seasonal forecasts.

I have been saying for awhile now, the early part of this year is likely to teach us a lot.
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495. DestinJeff 5:31 PM GMT on August 24, 2010

Problem is most people are saying both, so it really does not matter much
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Say it isn't so!

Big shift from the NOGAPS at 12z...hints that the ridge could still do tricky things, but recurvature east of the US is still most likely.

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Quoting JRRP:
OH oh ¬¬
Link

That is scary
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Quoting jasoniscoolman2010x:
LOOK AT THE RED WHERE INVEST 96L is.


And look at the hollow "TS" symbol on Danielle. It hasn't been a hurricane all morning....should be downgraded next advisory.
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492. JRRP

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storm is a good guy, and he offers a lot of experience and information to all of us. i have been a member of this blog for a few years now and i have never seen such disrespect,bickering, and childishness. everyday in this blog people are treating others like crap. reporting,poofing, and calling people trolls for asking questions, and offering opinions. all of these actions are ignorant. you can not call someone a troll and not be a troll yourself. you can not offer an opinion of your own, and turn around and say everyone else's opinion is crap. if your gonna poof someone for being a troll why do you have to engage in an argument by posting that you poofed that person and calling for others to do the same. this is all childish behavior and trollish in nature. all these issues are very easy to deal with. simply ignore those you don't agree with. if your not looking for a argument you won't feel the need to post your poof, and ask other to do the same. just ignore and move on. don't comment to post that aggravate you. personally i like to read all post and enjoy the difference of opinion. we are all throwing darts in here as mother nature is unpredictable.
Danielle seems to be falling apart, or just not as well defined as it was yesterday. wonder why?
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490. JRRP
OH oh ¬¬
Link
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Blog ate my post again.
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notice the direction in the TWO W
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Quoting Eagle101:


Thanks Levi...great work as always.

v/r

Jon
very good again
Member Since: October 19, 2005 Posts: 0 Comments: 234
Quoting sailfish01:
Levi - love your updates...kept them comimg


Thanks :)
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Quoting K8eCane:
I cant think of a single instance that the NHC wound up being wrong....just sayin


Ike....Frances....Katrina....Lili....Chris....list goes on. They are wrong just as many times as a lot of other people, but they do a great job most of the time.

If you can't think of a time they were wrong then you haven't been around long lol.
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Glad that Danielle has weakened a little, and it looks as if she continues to weaken. But! is that good? For it's future course I mean. Would have a little more of a "pole" bias if it stayed a Cat 2. Or was a Cat 3?
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471. DestinJeff 5:23 PM GMT on August 24, 2010

Right but it is fair to call it a loss in the 3rd inning like many try to do?

I think not, calling the season a bust now is just like saying your team is going to lose because they are losing in the 3rd inning.
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Here is one person that really appreciates Storm W. and his blog. I find it to be extremely informative and written in a way that us laymen can understand. Your knowledge of tropical systems and hard work is very much appreciated. Keep up the good work.
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Quoting FLdewey:
Awww.. now the "I'm leaving forever" posts are starting.


Noticed that. Now, when are we going to see yours? ;-)
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Quoting weatherguy03:


LOL. Oh I think the NHC has done well with this one. Its easy when all the models agree!..LOL Intensity forecasts are another story, still very hard to judge.


It's hard to argue with model consensus like Danielle has had since it was 95L
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Quoting FLdewey:
Awww.. now the "I'm leaving forever" posts are starting.



Looks that way doesn't it.Lol
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Levi - love your updates...kept them comimg
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473. JLPR2
Danielle seems to be eating the dry air but doing so is weakening.
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Quoting IKE:


NHC has done a great job on track.

Props to you folks in Coral Gables.


But they're not in Coral Gables anymore; they moved out to FIU after Andrew. But I know what you mean... ;-)
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THE CENTER OF HURRICANE DANIELLE AT 24/1500 UTC IS NEAR 16.6N
46.5W...OR ABOUT 985 MI...1585 KM E OF THE LESSER ANTILLES
...MOVING WEST 17 KT. THE ESTIMATED MINIMUM CENTRAL PRESSURE IS
985 MB. THE MAXIMUM SUSTAINED WIND SPEEDS ARE 70 KT WITH GUSTS
TO 85 KT. DANIELLE HAS WEAKENED DURING THE PAST SIX HOURS BUT
RE-STRENGTHENING IS POSSIBLE DURING THE NEXT 48 HOURS. PLEASE
READ THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
MIATCMAT1/WTNT21 KNHC AND THE LATEST PUBLIC ADVISORY UNDER
MIATCPAT1/WTNT31 KNHC FOR MORE DETAILS. SCATTERED MODERATE TO
ISOLATED STRONG CONVECTION IS FROM 14N-18N BETWEEN 44W-48W.
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Quoting IKE:


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.



Good afternoon Ike...I would say 40 miles is great considering all the variables.

Looks like we are in for more boomer's this afternoon...

Take Care.

v/r

Jon
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467. Asta
Quoting Levi32:
Heck....12z NOGAPS has Danielle getting caught under the ridge...


If she does that- could she pull a "Betsy" and cross FLA?
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I cant think of a single instance that the NHC wound up being wrong....just sayin
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Quoting Levi32:
12z CMC....put an eye on the western Caribbean. As Danielle recurves out, mischief to her southwest is very possible, assuming Earl doesn't quickly dart west. This is the first time I've seen anything but the NOGAPS hint at mischief occurring all the way down in the Caribbean, but it's certainly possible.


Thanks.
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Quoting IKE:


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.



It doesn't get much better than that
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A nice loop of eyewall to its current... plight.
Member Since: August 23, 2008 Posts: 7 Comments: 5300
a degree doesnt guarantee successful forecasting
it does however guarantee that you will make more money at forecasting JMO
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12z CMC....put an eye on the western Caribbean. As Danielle recurves out, mischief to her southwest is very possible, assuming Earl doesn't quickly dart west. This is the first time I've seen anything but the NOGAPS hint at mischief occurring all the way down in the Caribbean, but it's certainly possible.
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So this will be my last post on the main blog page. I came home this morning after working 12hrs. in florida, in the rain, taking care of the sick and injured. I read up on the updates and posted three questions. I know I am not a meterologist but I like to learn things, so I ask questions. When I wake up later today I waded through 150 or more post only to find alot of people whinning and moaning. It's like recees time in the fourth grade on here. All I wanted was a few scientific minded responses and the blog is so over loaded with BS (that's not bachlor in science either) that I can't even see my original post---

This blog has lost its value to me.

Have a good day and remember, threat your neighbor the way you would want them to treat you! (some people may due well to remember this rule - remember the golden rule)
Member Since: Posts: Comments:
I am just a naturally curious person that likes to "know". The existing parameters for an above-average season are already well known: La Nina conditions, high SST anomalies, lower-than average basin-wide shear, vigorous African lows, some overall pattern positives, etc.

But what are the negatives? The world is not black and white, it is in grey. I know we had a lot of ULL's this year. But why? That is the important question to me. I can see with my own eyes they were there. But the question to me once again is why? And what can we learn from that unexpected development, insofar as future forecasting goes?
Member Since: Posts: Comments:
Quoting Levi32:
12z GFS shifted west towards Bermuda....they should still be watching very closely.



it also takes 96L right over Bermuda later in the run
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454. IKE
Quoting DestinJeff:


I made a similar post earlier that was met with limited air-time and response.

Even used the graphics!


NHC has done a great job on track.

Props to you folks in Coral Gables.
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NHC has done a very good job with the track of Danielle
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Levi, Bermuda is not out of the sweepstakes for a Danielle visit and should continue to monitor the progress of this category 1 hurricane.
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Quoting nrtiwlnvragn:


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


Not sure. I snagged it from a Facebook post by WTSP-TV in Tampa Bay.
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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.