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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3099. Prgal
Good morning! I see we have TD7 already.
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He was being sarcastic
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That is some tasty vorticity with TD 7

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WOuldn't be completely surprised if 96L went directly to TS status. It looks that good.
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Quoting Tazmanian:
TD 7 is gone from the navy site heh


may be they are re nameing it


Click on any link on the Navy page, it will show up again.
Member Since: September 23, 2005 Posts: 15 Comments: 11341
you should start a surf forecast LOL can you post the current steering map?
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Quoting Thundercloud01221991:
Has anyone thought there is the possibility that Danielle and Earl will get close enough to each other to cause the (cant remember the name about rotating around each other) affect and will cause both of the storms at one time or another ot move westward and then southward and cause an impact on US that way


In case someone did not answer this: When 2 cyclones "orbit" around each other it's called the Fujiwhara Effect.
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I find it amazingly funny on how the GFS shifted west and the GFDL and HWRF models were on the eastern model guidance and now this morning the GFDL and HWRF have shifted west and the GFS shifted east
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1964: 'E' storm not until Sept 4th. 5th storm was Hurricane Cleo, named on Aug 20th. [Approaching 4-1-1; 12-6-6 by end].

1988: 'E' storm not until Sep 3rd. [3-0-0; 12-5-3 by end.]

1998: 'E' storm - coincidentally Earl (of Sandwich) - named on Aug 31st. [Approaching 4-2-1; 14-10-3 by end.]

2007: 'E' storm on Aug 14/15th. [5-1-1; 15-6-2 by end.]
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3086. NASA101
STORMW:

What do you make of recently designated PGI36L at 10W - 10N - definitely lots of convection West of the AOI with moderate vorticity!!

Thanks SIR...

http://cimss.ssec.wisc.edu/tropic2/predict/predict.php#
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So what do the models say about the wave over Ethiopia? Rumor has it that the GFS shows recurvature over central Chad. ;-)

Seriously though...interesting model split at the end of the run for Hurricane Danielle.
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TD 7 is gone from the navy site heh


may be they are re nameing it
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3081. Bonedog
Im baaaaack

Hey everyone =)
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4 of the 6 models on this graphics now hook Danielle back west very close to Bermuda. Those include the GFDL and HWRF. Only the UKMET and GFS sharply curve Danielle out. This should be monitored VERY closely.
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Quoting AllStar17:
Either the blog is eating a lot of posts or it is oddly quiet. I understand there is school, but I did not think that many on this blog were that young.

Many of our younger bloggers especially in the South are back at school.
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DANIELLE..... even with all the models so close together
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Quoting StormW:
Sure glad the season is slow:



StormW being a bit sarcastic again this morning:)
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3074. RJT185
Quoting Relix:

It has eaten twice mine =P


Seems like a trend this morning!
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3072. Sting13
Why are some of the models now shifting back west at end of run, is there an unforeseen high building in? Kind of runny just a few days ago this was going out to sea in middle of ocean.
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Quoting StormW:
Here's a nice one:

DANIELLE


She's a stuborn one. She just doesnt want to go north of 20? Nice intensity
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Quoting StormW:


Taz...don't let the cat out of the bag!



or the cat may get you


run
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storm you nailed it AGIAN
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3067. divdog
Quoting AllStar17:
Either the blog is eating a lot of posts or it is oddly quiet. I understand there is school, but I did not think that many on this blog were that young.
no current u.s threats seems to slow things down. subject to change as always
Member Since: August 22, 2008 Posts: 0 Comments: 755
3065. angiest
Quoting AllStar17:
Either the blog is eating a lot of posts or it is oddly quiet. I understand there is school, but I did not think that many on this blog were that young.


Seems to be eating posts again.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
3064. Relix
Quoting AllStar17:
Either the blog is eating a lot of posts or it is oddly quiet. I understand there is school, but I did not think that many on this blog were that young.

It has eaten twice mine =P
Member Since: August 3, 2006 Posts: 0 Comments: 2741
3063. angiest
Quoting StormW:
Sure glad the season is slow:



Take 2 on this.

Looks like there are even some future waves currently out in Indian Ocean.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting Jeff9641:


LOL! Morning StormW. Looks like we are going to be spitting off CV storms left and right. I am concerned though in like the 8 to 10 day period as it looks like a maasive ridge is going to setup in the east. If that happens then we could very well see some of these systems target the US.
I was viewing the same thing which is why I am discounting some of the model guidance on 96L
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Either the blog is eating a lot of posts or it is oddly quiet. I understand there is school, but I did not think that many on this blog were that young.
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Quoting StormW:


Yes sir!



are you JFV?



heh heh heh this playing
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I've wondered about this each time I see it.. what is that red coloring that shows up on satellite imagery (shortwave) from time to time - you can see it at the end of this run at what I think is 40W/5N?:

Link
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3055. RJT185
Quoting AllStar17:
It's important to note that several of the computer models take TD 7 immediately to the west-northwest. However, it really has been moving due west for the past 12 hours or so, so more left shifts in those tracks would seem likely:


Intensity will be the key in how soon/late TD7 would begin embracing the northernly components the current and future atmospheric setup would offer.
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TD 07L 30kts-1007mb-142N-303W

Visible picture.





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It's important to note that several of the computer models take TD 7 immediately to the west-northwest. However, it really has been moving due west for the past 12 hours or so, so more left shifts in those tracks would seem likely:
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Quoting StormW:
Sure glad the season is slow:

LOL
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3049. RJT185
Thanks for the MJO data Storm, it'll be a HECK of a September for forecasters!
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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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