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 CosmicEvents:
As I understand it, the long-term forecast for Danielle, from advisory #1 and continuing now, has always called for greater uncertainty on Day 4-5 due to the balance of the exact timing of the cyclone's speed and the where and when of it's strength. Since the first advisory, the storm at first strengthened faster than expected, then weakened more than expected. Still, with all this, it's averaged out so that the storm has been well within any NHC cone in the 3-5 day period. That's good, isn't it? Doesn't the NHC themselves say that their is a signifigant amount of the time(20-30%??) the storm will find itself outside of the cone 120 hours out? So far, with Danielle, she's been in the cone. The NHC...in the zone.


The very first advisory has verified well, however subsequent advisories not so good. If you look at the model performance tracking from hurricane.methaz.org the current average errors are:

model Error Trend 24hr Error 48hr Error 72hr Error
OFCL INCREASING 91.4 108.6 23

The NHC radii for 24 hours is 62 n mi, so well outside the cone. For 48 hours 108 n mi, so just at the cone.
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1347. BDAwx
Umm. False.
Fabian was definitely a cat 3. I think the NHC nailed it by calling it a 120mph storm as the highest official winds were estimated to be 115mph on the eastern end of the island whilst reports of even stronger winds in the west end, which was deeper into the eyewall.unofficial gusts well above sea level reached 143kts. or 164mph.

Fabian was by all means a disaster for Bermuda. many areas were without power for longer than a week some for up to 6 weeks. Schools were damaged, some south shore hotels were deemed uninhabitable. The airport, the causeway between mainland and st. george's, and most of the south shore beaches were essentially washed away. Thousands of trees were uprooted and the remaining ones were severely defoliated. On top of that a good amount of people had some sort of property damage be it to their roof or to a boat they owned, or a car.

Generally Bermuda does do fine in Hurricanes. Fabian was a major hurricane. we do better than most in a major hurricane but not fine by the majority of accounts.
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Quoting extreme236:
Another disturbance comes off Africa in 36 hours. Nothing signficant there yet though in the run.
Might be the wave appearing on the right side of the image below.

Member Since: September 2, 2009 Posts: 130 Comments: 21194
1345. Patrap

GOM IR Loop





Member Since: July 3, 2005 Posts: 428 Comments: 129795
1344. Engine2
Quoting StormW:


I think we will see another adjustment left, and I believe the "good" turn will take affect around 53-55W.
agreed - storm do you think the system is not vertically stacked or the center is relocating?
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1342. xcool
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1340. Skyepony (Mod)
Looks like a big anticyclone formed over MS this morning causing very low shear in the area..Since it's been drifting south toward the wanna be blob in the Gulf of Mexico.
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Quoting CaneAddict:
My forecast.

Bingo, looks spot on to me, except I think a bit further west.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
1338. jonelu
Ya...she is firing up and becoming more symmetrical.....
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Now the GFS wants to develop a third storm behind Danielle and future Earl.
Member Since: June 29, 2006 Posts: 65 Comments: 3197
Quoting eliteforecaster:


I agree, I wish they would run the Super Rapid Scans more often.


Well, it is alot of data. Do you know how often they do it? I wish they had been able to do one with Alex, although the angle it took it from was nice in giving some depth.
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I believe I just put in another order change for plushy toys. The blog hole has to lead to somewhere.
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1334. xcool
ROBTX09 HMM STALLED ?
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1333. IKE
Quoting jurakantaino:
the majority of the construction in our island close 95% is cement. Most of our problems when this systems strikes are because the floods and landslides. Well Dannielle hasn't been hype by us, since we haven't been the CONUS, but of course nothin is written on stones and when ever there is a system east or SE of our Islands we worry! What about a last minute turn to the left, there is always a possisibility.


I think you are safe from Danielle.
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Quoting neonlazer:


That has got to be one of the coolest satellites ever! haha...so cool to watch it minute by minute and also the nice resolution. Can see details in the storms as they grow.


I agree, I wish they would run the Super Rapid Scans more often.
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The 18Z GFS shows a weaker trough, strong ridging..
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oh my lord - it's 104 degrees here - 90 miles north of san francisco!
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Member Since: July 6, 2010 Posts: 113 Comments: 32805
My forecast.

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Another disturbance comes off Africa in 36 hours. Nothing signficant there yet though in the run.
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Member Since: July 6, 2010 Posts: 113 Comments: 32805
What he said, I am from NS too.

Quoting Sting13:
Storm, do you feel the models are going to keep shifting west or is this about it? They have been going west all day. The reason i ask is because earlier the GFS had danielle just off the coast of nova scotia, and the closer to bermuda it gets, the less time it has to curve out to sea :|
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72:

Member Since: July 6, 2010 Posts: 113 Comments: 32805
Quoting CosmicEvents:
As I understand it, the long-term forecast for Danielle, from advisory #1 and continuing now, has always called for greater uncertainty on Day 4-5+ due to the balance of the exact timing of the cyclone's speed and the where and when of it's strength. Since the first advisory, the storm at first strengthened faster than expected, then weakened more than expected. Still, with all this, it's averaged out so that the storm has been well within any NHC cone in the 3-5 day period. That's good, isn't it? Doesn't the NHC themselves say that their is a signifigant amount of the time(20-30%??) the storm will find itself outside of the cone 120 hours out? So far, with Danielle, she's been in the cone. The NHC...in the zone.


Good point if it is in the cone that is in the realm of a possible track.
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Hour 66:

Member Since: July 6, 2010 Posts: 113 Comments: 32805
18z GFS says get ready Bermuda...a hurricane is coming for you. At least it appears that way through 72.
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1318. xcool
GFS MUCH slowly JMO
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Quoting smuldy:
i just plused it-get broadband people its not 1993 and it is free now in a lot of cities


Doesn't matter, still slows down the page, and not everyone lives in a city. And there is no free broadband anywhere, not even in ice cold Europa. Wireless crap from Starbucks or a freezer is not broadband.
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1316. Sting13
Storm, do you feel the models are going to keep shifting west or is this about it? They have been going west all day. The reason i ask is because earlier the GFS had danielle just off the coast of nova scotia, and the closer to bermuda it gets, the less time it has to curve out to sea :|
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Quoting IKE:


That's one thing I've notice about Danielle and PR. I haven't seen one post from anyone in Puerto Rico that acted like they were frightened over Danielle.

Either...(a)they trusted the official source...the NHC,...or...(2)what you say is true...or both.

Props to PR bloggers! No hyping up and scared to death posts by any of you.
the majority of the construction in our island close 95% is cement. Most of our problems when this systems strikes are because the floods and landslides. Well Dannielle hasn't been hype by us, since we haven't been the CONUS, but of course nothin is written on stones and when ever there is a system east or SE of our Islands we worry! What about a last minute turn to the left, there is always a possisibility.
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Quoting eliteforecaster:


Well its removed now...no idea why, but whatever.


For those who missed it, here is the latest SRSO (Super Rapid Scan Operation) on Danielle from Goes-15. The animation ends at 4:34 est.



Taken from Here.


That has got to be one of the coolest satellites ever! haha...so cool to watch it minute by minute and also the nice resolution. Can see details in the storms as they grow.
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Through hour 63, the GFS is slightly farther west with Danielle. Future Earl is in the same spot as 12z, but it's stronger.
Member Since: June 29, 2006 Posts: 65 Comments: 3197
Quoting tpawxguy:
Under the header, "A fool and his money". I was talking to a buddy today at AccuWeather and he said they were informed Orange Juice futures skyrocked today. Why? Bloomberg business said it was because of the fear of a hurricane hitting Florida next week. I couldn't help thinking the Duke brothers were involved somehow!!


eggs have already skyrocketed.
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Hot tower?

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Hour 60:

Member Since: July 6, 2010 Posts: 113 Comments: 32805
Quoting Tazmanian:
am going too read Danielle a bed time story too help it get get stronger


I think that would put her to sleep.
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1307. xcool
she ramp-up noww .wnw
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As I understand it, the long-term forecast for Danielle, from advisory #1 and continuing now, has always called for greater uncertainty on Day 4-5+ due to the balance of the exact timing of the cyclone's speed and the where and when of it's strength. Since the first advisory, the storm at first strengthened faster than expected, then weakened more than expected. Still, with all this, it's averaged out so that the storm has been well within any NHC cone in the 3-5 day period. That's good, isn't it? Doesn't the NHC themselves say that their is a signifigant amount of the time(20-30%??) the storm will find itself outside of the cone 120 hours out? So far, with Danielle, she's been in the cone. The NHC...in the zone.
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18z GFS Hour: 054



Hey All
Member Since: July 6, 2010 Posts: 113 Comments: 32805
I believe she is going to past west of Bermuda
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Quoting FLdewey:
Large loops like that slow down the page... so after 10 people can't take it and minus it - it's disappeared. You're not banned, you're just tossing out internet stop sticks. ;-)


I see it now...
actually, that is a nice loop!
Member Since: August 29, 2009 Posts: 12 Comments: 483
1299. Max1023
Guys link to large loops, don't post them. It saves space and speeds the blog up.
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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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