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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Hey, look, Sherlock Holmes is in the blog today...

Clearly.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting IKE:
If it follows the center of the track, the NHC has, Bermuda will be 150 miles west of where she goes. They'll survive.


Wow I was not aware that the center line was exactly where the storm was going to go

You did see the part where the NHC said their track shifted a full 2 degrees further west by day 5 right?

But whatever you know where the storm is going to go right? How about you just tell us from now on and we ignore the NHC?
Member Since: March 10, 2010 Posts: 1 Comments: 7818
Quoting IKE:


That should start up after Danielle passes Bermuda. Buckle up...the westcasting and slamming into Florida could get hot and heavy.


I'm sure it'll be annoying, but it can't be worse than NOLAcasters anytime storms pop up in the Carib and Gulf. They're both annoying
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1245. Max1023
General rule for 5 day forecasts: If you are right on the track line you are safe. Anywhere else and you are in trouble. lol

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Looks like we could have something brewing off the Carolina coast. CMC has been showing development for the past couple of days.

While it's likely to be sub-tropical, may be something that needs to be watched.

Link
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1243. Dakster
Quoting ElConando:


I'm still big, its the pictures that gotten small.


Thanks and true...
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Quoting belizeit:
To me it looks like Daniele is moving west again and if this keeps on going in this direction we should see the hurruicane hunters fly out on thursday to invest the sytem as it would be west of 55


The westerly bias has been right more times than not. Now she is back into the Bermuda box. Either way... it will be a body-surfing weekend at the beach.
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.
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Quoting IKE:


If it follows the center of the track, the NHC has, Bermuda will be 150+ miles west of where she goes. They'll survive.


It won't.
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Quoting ElConando:


I'm still big, its the pictures that gotten small.
Sure have in the funny pages section.
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1226. SFlKatCane5 9:37 PM GMT on August 24, 2010

What are you Ace Venduta blog detective?
Member Since: March 10, 2010 Posts: 1 Comments: 7818
Quoting IKE:


If it follows the center of the track, the NHC has, Bermuda will be 150+ miles west of where she goes. They'll survive.
the construction in bermuda is like puerto rico, everything is concrete, we are well prepared for storms
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1232. IKE
Quoting TopOfTheLakeFL:
im surprised there is not more talk about 96L and its forecast track.. despite it being early its still newsworthy.. especially if ev1 believes danielle just a fish storm.. maybe time to shift focus to the potential earl?? unless danielle isnt done yet.. the models seem to be shifting slightly westward..


That should start up after Danielle passes Bermuda. Buckle up...the westcasting and slamming into Florida could get hot and heavy.
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Quoting IKE:


If it follows the center of the track, the NHC has, Bermuda will be 150+ miles west of where she goes. They'll survive.


Yes but that doesn't really matter at 5 days out. Bermuda is in the cone now so they should start keeping tabs on in it in a couple days if need be.
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1230. Max1023
Quoting ElConando:
Well Danielle looks like it is trying to intensify again. We shall see what happens.


Danielle has a strong LLC from it's time as an 85 knot storm, it has a lot more to work with than many storms after a weakening trend. All it would take is a reduction of shear to bring this back to a hurricane, in fact I would not be surprised if there are 65 knot winds under that heavy convection right now.
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1228. xcool


move wnw.
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Quoting belizeit:
To me it looks like Daniele is moving west again and if this keeps on going in this direction we should see the hurruicane hunters fly out on thursday to invest the sytem as it would be west of 55

is this some sort of hermaphrodite storm?
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im surprised there is not more talk about 96L and its forecast track.. despite it being early its still newsworthy.. especially if ev1 believes danielle just a fish storm.. maybe time to shift focus to the potential earl?? unless danielle isnt done yet.. the models seem to be shifting slightly westward..
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Well Danielle looks like it is trying to intensify again. We shall see what happens.
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1223. Dakster
Quoting StormW:


I used to read...now I just listen to the pictures.


What about the voices?
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1222. IKE
Quoting SFlKatCane5:


I'm actually surprised by that number of six homeless, as homeless are not allowed in Bermuda.


If it follows the center of the track, the NHC has, Bermuda will be 150+ miles west of where she goes. They'll survive.
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Quoting Hurricanes101:


I used to read too, but now I just follow forecast models
Hehehe, I like that one.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting StormW:


I used to read...now I just listen to the pictures.


I'm still big, its the pictures that gotten small.
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1219. Max1023
One thing about Danielle is that it is putting a lot of moisture into the central Atlantic. Any storm which follows a similar track will not have to contend with quite as much dry air. Upwelling will be significant however this time of year SST's south of 20N will recover quickly, as the subsonic point still travels north of the equator.
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Quoting StormW:


I used to read...now I just listen to the pictures.


I used to read too, but now I just follow forecast models
Member Since: March 10, 2010 Posts: 1 Comments: 7818
Quoting StormW:


I use to read...now I just listen to the pictures.
Sounds like StormTop...doesn't read what you write, but instead just looks at graphics that show TUTT's and dry air. :)
Member Since: September 2, 2009 Posts: 130 Comments: 21194
To me it looks like Daniele is moving west again and if this keeps on going in this direction we should see the hurruicane hunters fly out on thursday to invest the sytem as it would be west of 55
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1207. Dakster
Quoting Floodman:


You know how it goes...too much pressure an "POP goes the weasel!"

LOL

Glad to see you in here more these days...


trying to stay up with it... But work and life gets in the way sometimes!

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1206. IKE
Hurricane Bill in 2009 passed within 120-150 miles to the west of Bermuda. So Bermuda got the worse side of Bill.

According to Wikipedia....

"The hurricane had little impact in Bermuda. A public high school was designated as an emergency shelter, into which The Salvation Army took six homeless people. Some 3,700 households experienced power outages at some point during the storm, and in some instances cable television and internet services were also interrupted, particularly in the central Spanish Point headland. During the daytime on Saturday, public works crews performed cleanup of light debris, mostly discarded garbage unveiled by the storm.
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I wish I could post the plot of every ECMWF Ensemble member. There are so many possible solutions on there. The westernmost solution comes up the East Coast of the U.S. and the easternmost solution harmlessly curves way east of Bermuda. The consensus, if you could call it one, is that Danielle gets to 60W and recurves. Everything is up in the air at this point. You can't completely count anything out until the solution brought up seems impossible to occur.
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1204. Max1023
It's possible that Danielle could become a Category 4 Hurricane at some point, as the SST threshold for that strength is about 28.5 degrees. Water that warm extends to north of 30 N and East of 50 W. IF Danielle runs into a pocket of ideal upper level conditions and has a low forward speed to reduce the effects of dry air it is possible. However at the time it seems unlikely, as upper level conditions are not ideal by any respect. If the upper level anticyclone redevelops then we might see a major, otherwise Cat 2 is likely Danielle's maximum potential.
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am l seeing right. is there a centre relocation to the southwest 16N 48w moving southwest?
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Quoting pottery:

Can you READ???
Someone needs Rosetta Stone...

:)
Member Since: September 2, 2009 Posts: 130 Comments: 21194
1200. Engine2
I'm waiting for the visible to update, I really think the center is now south and west from the previous spot unless its not vertically stacked
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Quoting StormW:


You betcha, Shen...we got jeans, T-shirt, and your choice of bandanna.


Can I be too lol
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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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