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 StormW:
Hot off the press!

HURRICANE DANIELLE / TROPICAL DEPRESSION SEVEN SYNOPSIS AUG. 25, 2010


Thx for the update StormW.. Appreciate!
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Model after model had Ike going east of Bermuda. When the first trough had little effect on him. the NHC went into oh $%^# mode.
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3347. NASA101
Hoenn:

You are fast becoming an irrelevant blogger with your utter nonsensical comments!!
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Quoting hoenn:
throw the models for danielle out

i think she is going to the gomex

she hasn't moved north at all


Everyone sing along now:

Wholly ridiculous...**POOF!**
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Quoting Relix:
Earl looks like a close northern islands skirt and an FL EC event while future Fiona seems to aim at the Caribbean and islands. Daaayuuum.


You can't just say it will be some state event when its way out there... There's no way of knowing that just yet.. Its just ur opinion.. But a lot of things can change.. So after 3 days it can change.. so I wouldnt believe the models that far out.. It has a chance of happening but we have to wait and see.. Plus to add a panic of nonsense.. :/
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Quoting hoenn:


it will hit florida then lousianna
what do you see that makes you think this? thanks in advance
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Quoting Melagoo:
If EARL hits the USA ... EARL CAMPBELL (Hurricane) vs JACK LAMBERT (USA)


Jack will win
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3339. XStormX
Quoting Relix:
Earl looks like a close northern islands skirt and an FL EC event while future Fiona seems to aim at the Caribbean and islands. Daaayuuum.
if earl keeps going at 275 degrees, it might something to watch
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Quoting NASA101:


PLEASE stop posting utter rubbish!!

??? I apoligize if that offended you , I summed up what the majority of what everyone else is saying?
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Quoting calder:


Danielle still is forecasted to miss bermuda on the east. Model consensus shifted back this morning.
Bermuda is in the cone of error. When danielle was at TD7's position it was forecast to move past bermuda hundreds of miles to the east.
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3325. Check who you quote before you type!
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If you look at the Atlantic full shot you can see that the two tropical systems Danielle and TD 7 are directly connected by one rope of clouds.

Kind of cool!!!
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3331. wxhatt
Quoting will45:


they are too young for prozac


LOL, we have too may "Doom Casters", they wouldn't be saying that if they were staring a major hurricane for there city...
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3330. Michfan
Quoting hulazigzag:
Facts please


There are no facts here. Only hyperbole. LOL.
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3329. K8eCane
wake me up when september ends
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3326. Relix
Earl looks like a close northern islands skirt and an FL EC event while future Fiona seems to aim at the Caribbean and islands. Daaayuuum.
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3325. K8eCane
Quoting mydiapersarefull:
Yep...eastern North Carolina strike is the first thing I think about with this system.

easy there, chief....



How can anyone say eastern NC strike? actually though he said its the first thing he thinks about so my bad
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Quoting KanKunKid:
So where is the chart showing this much touted trough that's gonna suck Danielle to the north?
Hmmmmm?



The trough that I heard from yesterday was supposed to head east where the High Pressure to danielle's north was to weaken.. Then the trough would pick her up either when she is close to bermuda or past it.. But I havent checked any maps or new models lately..

Im going to check and see for sure.. I hope this helps in a way..
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3323. 7544
earl for so fla maybe
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3322. XStormX
Earl later this after noon?
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3321. wxhatt
Quoting Alockwr21:


Yep...eastern North Carolina strike is the first thing I think about with this system.


How can you say this far out. There's so much time and area to cover first...
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3320. angiest
Is stormtop back? I see more trolls today...
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3319. Melagoo
Bermuda has had their deflector shield in place for over two weeks now Danielle won't touch Bermuda
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3316. will45
Quoting hurricanehanna:
time to pass out the prozac...line up kids


they are too young for prozac
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Yep...eastern North Carolina strike is the first thing I think about with this system.

easy there, chief....
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3314. angiest
Quoting ILwthrfan:


I don't know about a cat 5, I do agree that "pre" Earls environment is definitely going to be more moist than Danielles, but He's going over churned up waters, not to mention he's contengent on what Danielle does... IF she Strengthens and stays within arm reach of Earl, Earl won't be much, but if he can get away from her, he's got potential to make people nervous.


Danielle has been moving about 15-20 kts most of her life. I don't think she has hung around anywhere long enough to churn up waters to any significant degree. Of course, I could be wrong.

Early is more likely to suffer from being in Danielle's propwash. That is, if she gets enough outflow going.
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Quoting calder:


Danielle still is forecasted to miss bermuda on the east. Model consensus shifted back this morning.
Really? Proof? I looked at all these models and thats not whats being projected.
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Quoting hoenn:
earl will be the most intense hurricane on record

mark my words

earl means business

Facts please
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3310. NASA101
Quoting ILwthrfan:


I don't know about a cat 5, I do agree that "pre" Earls environment is definitely going to be more moist than Danielles, but He's going over churned up waters, not to mention he's contengent on what Danielle does... IF she Strengthens and stays within arm reach of Earl, Earl won't be much, but if he can get away from her, he's got potential to make people nervous.


PLEASE stop posting utter rubbish!!
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3309. MahFL
THE BLOG WILL NOW EXPLODE !
3 2 1 .....
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3308. calder
Quoting hulazigzag:
too far out to tell yet. remember danielle was forecast to miss bermuda well to the east. thats not panning out.we have no skill in such long range forecasts.


Danielle still is forecasted to miss bermuda on the east. Model consensus shifted back this morning.
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3307. Melagoo
Quoting hoenn:
earl will be the most intense hurricane on record

mark my words

earl means business



That remains to be seen ... I'm sure EARL will be a Hurricane ... if he ever reaches the GOM you may be right
Member Since: July 31, 2006 Posts: 19 Comments: 1579
Danielle is still, currently moving wnw, with speed of 17mph and is still at 85 mph winds. The only thing changed is the coordinates. Look at TD 7, the 5 day forecast doesn't show a storm going out to sea but looks like it may hit the U.S. Coast. I know things can change, both H.Danille and the newly formed TD 7, look to be giving us some problems in the next week or so.jmo
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time to pass out the prozac...line up kids
Member Since: September 5, 2007 Posts: 0 Comments: 3488
Quoting hoenn:
earl will be a cat 5

danielle moist up the ocean for him




I don't know about a cat 5, I do agree that "pre" Earls environment is definitely going to be more moist than Danielles, but He's going over churned up waters, not to mention he's contengent on what Danielle does... IF she Strengthens and stays within arm reach of Earl, Earl won't be much, but if he can get away from her, he's got potential to make people nervous.
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Quoting tropicfreak:


It looks like it may pull off an Isabel.


Yep...eastern North Carolina strike is the first thing I think about with this system.
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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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