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 reedzone:
12Z GFDL has shifted westward quite a bit as well... EURO is next! Also the GFDL now has 96L westward.


Wow the GFDL is very far south with 96L too

has it at 20N and 54W in 5 days
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Quoting FranAteMyRoof96:

I was in Hillsborough then, and when it quieted down at about 2am we thought it was over...then woke up 45 minutes later when the house started shaking and the trees started cracking and falling.



LOL when the eye passed over, my neighbor yelled to me that she and her sister had seen an "apparition" in the yard during the storm
Her husband told her "its called a hallucination" LOL...They still argue us down that they both saw it
he said "well yall are sisters. you see the same thing"
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Big shift west on the models:

0z


06z


12z Early


12z Late
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12Z GFDL has shifted westward quite a bit as well... EURO is next! Also the GFDL now has 96L westward.
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Quoting DestinJeff:
Looks to be due South of 2nd TFP and bending w/wsw

Link



Whoa...could this defy most models?
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Quoting DestinJeff:
Looks to be due South of 2nd TFP and bending w/wsw

Link

if it misses it wont be by much
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Quoting ticka1:
Anyone have comments on the GOM if anything will form out of the frontal boundary that's hanging out across the GOM?


From experience this year, I wouldn't count on anything significant developing. If anything tropical does develop, it will likely take 3 days at least because there is a lot of dry air and shear. The Caribbean and GOM have become more hostile for development rather than favorable during a time it should be optimal. Really confusing.
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Quoting K8eCane:


Yeah I remeber her too...I am very near the coast at Wilmington and the eye went over me too...now she was a bad one...Im in a brick home and it was swaying

I was in Hillsborough then, and when it quieted down at about 2am we thought it was over...then woke up 45 minutes later when the house started shaking and the trees started cracking and falling.
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Quoting DestinJeff:
Weakness to north closing off?

Interesting.....
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mm Lots of activity seen on the GFS 12Z run!
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Quoting ticka1:
Anyone have comments on the GOM if anything will form out of the frontal boundary that's hanging out across the GOM?
environment has to improve before anything is going to happen. no model support at this point that I know of.
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Quoting FranAteMyRoof96:

I don't think so...my avatar is Fran...


I may be thinking of Felix:

Felix

The subtropical ridge built to the west, forcing Felix to take a west-northwest track. Initially, it appeared that the westward motion would cause Felix to strike the mid-Atlantic coastline, though a weakness in the ridge caused the hurricane to stall just 165 miles (266 km) east of the Outer Banks from August 17 to August 19. Cooler, drier air weakened Felix to a minimal hurricane, and while stationary, it presented an eye 60 miles (97 km) to 80 miles (130 km) in diameter. After one shortwave trough failed to pull the hurricane towards open sea on the 18th, Felix drifted eastward, and executed a clockwise loop before another shortwave trough brought the hurricane to the northeast. Cooler waters weakened Felix to a tropical storm on August 20, and after passing to the east of Newfoundland, the storm became extratropical on the 22nd. As an extratropical storm, Felix persisted until August 25 when it dissipated between Iceland and Ireland.[1]
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583. JLPR2
Quoting AllStar17:


We have an LLC....it needs to tighten up.


A not well defined and broad low, has to tighten and get a nice LLC.
Not saying it doesn't have one per se, it just isn't enough to be qualified a TD, not TD material yet.
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Quoting kwgirl:
I have been a lurker for sometime now, but this discussion has led me to put my 2 cents in. I have lived in Key West since my family followed Hurricane Donna down the Keys (1960). The season is just starting! We used to have tropical storms in June and July (cooled off the summer heat)and nothing really big til after school started in late August. Going back in Key West history, there were a couple of Hurricanes in Oct. 1910-1911 that did significent damage. I sat three days in shelter for Hurricane Betsy, maybe 100 yards from the Gulf. First and Last time for a public shelter! The NHC has come a long way with forecasting storms. I think the margin for error has greatly decreased over the years.


Great post! As a long time fellow South FL resident (Broward) I completely agree with you.
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Quoting FranAteMyRoof96:


Also Fran, 1996. We lost power (200 miles inland) just before she made landfall, and the track at that point still had her moving up the coast. She never turned and the eye passed right over my house.


Yeah I remeber her too...I am very near the coast at Wilmington and the eye went over me too...now she was a bad one...Im in a brick home and it was swaying
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Bertha ate my roof 1st then Fran ate my blue tarp right after!
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579. TGTTX
Quoting angiest:


That is, to a point, true. Especially Galveston's mayor taking too long to make a decision. But the NHC kept forecast Cat3/4 effects from Ike but stubbornly refused to up the winds by 1mph to make him a three. A *lot* of people made decisions based on that 1mph difference between 2 and 3. Ike clearly had the pressure of a major and the ability to do severe and catastrophic damage, worthy of cat 4 designation, but the NHC's decision not to go with the pressure caused local governments to make, or not make, some decisions with regards to evacuation. Ike was a very close thing, just about 10-20 miles south would have made for a much, much worse situation.


+1,000,000 -- Time to restart the old Saffir-Simpson scale debate. System was inappropriate for assessing Ike, and created false sense of security that the storm wouldn't be serious.

We could talk about Rita, too. That cone moved a long way North in the course of a short period of time. StormW was way ahead of NHC on that one. The fact I was reading him here allowed me to better prepare and get out of town ahead of the rush.
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Anyone have comments on the GOM if anything will form out of the frontal boundary that's hanging out across the GOM?
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577. JLPR2
111 °F
-.-

I don't like that heat index, I'm melting! :S
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Quoting angiest:


Is Fran the one that, for a time, had a ridiculously large eye?

I don't think so...my avatar is Fran...
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Quoting StormW:


And mine aren't? Because, a lot of people see "degree" or Ph.D, and right away, that's the law of the land, and heaven forbid of you disagree, or even sometimes, out perform them. And that's garbage.



StormW, your being modest IMO. You are tolerent and attempt to be helpful to all but the most insincere inquiries. You are professional and refrain from "guiding" the scientific data to support a predetermined disposition. You are the real deal and people know it.

Pretenders come in both degreed and sans-degreed varieties. The discussion in this place is only helpful if folks refrain from "force fitting" every storm into either the apocalyptic or benign variety. Few are the former but when they are, the credibility of folks like you shines through.

Crying wolf every single time an L develops serves no purpose.
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Quoting FranAteMyRoof96:


Also Fran, 1996. We lost power (200 miles inland) just before she made landfall, and the track at that point still had her moving up the coast. She never turned and the eye passed right over my house.


Is Fran the one that, for a time, had a ridiculously large eye?
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Quoting JLPR2:


In other words as soon as we get a LLC we get a TD.


We have an LLC....it needs to tighten up.
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Quoting Levi32:


Yeah, well you gotta remember I don't remember anything before 2003 lol. I mentioned Lili because I saw that one on the news when I was little, but yeah, Floyd was one I missed.


Also Fran, 1996. We lost power (200 miles inland) just before she made landfall, and the track at that point still had her moving up the coast. She never turned and the eye passed right over my house.
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570. SLU
553. angiest 1:48 PM AST on August 24, 2010

Latest funktop image has a patch of green


yep
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Quoting ShenValleyFlyFish:
Depends a little on how many days out you count. I don't know about the others but if you stick to 3 day cone on IKE they didn't do badly. Response from public leaders caused a lot of complacence with IKE and contributed to the size of the tragedy IMHO. I can't speak to the others as didn't follow them as closely.


That is, to a point, true. Especially Galveston's mayor taking too long to make a decision. But the NHC kept forecast Cat3/4 effects from Ike but stubbornly refused to up the winds by 1mph to make him a three. A *lot* of people made decisions based on that 1mph difference between 2 and 3. Ike clearly had the pressure of a major and the ability to do severe and catastrophic damage, worthy of cat 4 designation, but the NHC's decision not to go with the pressure caused local governments to make, or not make, some decisions with regards to evacuation. Ike was a very close thing, just about 10-20 miles south would have made for a much, much worse situation.
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568. JLPR2
Quoting btwntx08:
554. jasoniscoolman2010x 5:48 PM GMT on August 24, 2010
A WELL-DEFINED CENTER HAS
NOT YET FORMED. that means no tropical d today

???
AN AREA OF LOW PRESSURE LOCATED ABOUT 150 MILES SOUTH-SOUTHWEST OF
THE CAPE VERDE ISLANDS CONTINUES TO SHOW SIGNS OF ORGANIZATION.
HOWEVER...SATELLITE DATA INDICATES THAT A WELL-DEFINED CENTER HAS
NOT YET FORMED.
THIS SYSTEM COULD BECOME A TROPICAL DEPRESSION AT
ANY TIME
AS IT MOVES WEST-NORTHWESTWARD NEAR 15 MPH. THERE IS A
HIGH CHANCE...90 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL
CYCLONE DURING THE NEXT 48 HOURS. LOCALLY HEAVY SHOWERS AND STRONG
GUSTY WINDS OVER THE SOUTHERN CAPE VERDE ISLANDS SHOULD BEGIN TO
DECREASE LATER TONIGHT OR ON WEDNESDAY.
forgot to read the blod part mr


In other words as soon as we get a LLC we get a TD.
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I have been a lurker for sometime now, but this discussion has led me to put my 2 cents in. I have lived in Key West since my family followed Hurricane Donna down the Keys (1960). The season is just starting! We used to have tropical storms in June and July (cooled off the summer heat)and nothing really big til after school started in late August. Going back in Key West history, there were a couple of Hurricanes in Oct. 1910-1911 that did significent damage. I sat three days in shelter for Hurricane Betsy, maybe 100 yards from the Gulf. First and Last time for a public shelter! The NHC has come a long way with forecasting storms. I think the margin for error has greatly decreased over the years.
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Quoting Levi32:


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.
Depends a little on how many days out you count. I don't know about the others but if you stick to 3 day cone on IKE they didn't do badly. Response from public leaders caused a lot of complacence with IKE and contributed to the size of the tragedy IMHO. I can't speak to the others as didn't follow them as closely.
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Quoting jasoniscoolman2010x:
A WELL-DEFINED CENTER HAS
NOT YET FORMED. that means no tropical d today


THIS SYSTEM COULD BECOME A TROPICAL DEPRESSION AT
ANY TIME AS IT MOVES WEST-NORTHWESTWARD NEAR 15 MPH.
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Quoting angiest:


Not quite as bad, but we were in the Rita evacuation with my wife about 6 months pregnant. As anyone who has had to deal with a pregnant woman can tell you, they are not pleasant when there is no easy access to restrooms. ;)


I bet lol.
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AL, 95, 2010082118, , BEST, 0, 108N, 318W, 25, 1008, TD, 0, , 0, 0, 0, 0, 1012, 300, 75, 35, 0, L, 0, , 0, 0, INVEST, S,
Member Since: August 18, 2010 Posts: 0 Comments: 42
In Dr. Masters probability graphic, did anyone notice the 95% chance that one of these2 storms will hit the great lakes?
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Quoting duajones78413:


renumber what?


96L->07L
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Quoting Hurricanes101:


if the nhc says there is yet a well defined center, I doubt it gets a renumber yet


renumber what?
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Quoting SLU:
Improving.



Latest funktop image has a patch of green in it.
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CDO back over Danielle's center.

Will she keep it? Film at 5.
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No TD7 until probably 11pm, needs to tighten its LLC, it has one, just needs to get tighter.
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550. SLU
Improving.

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Quoting nrtiwlnvragn:



This is a graph I have been working on, so don't laugh too hard. It shows the verification error for each forecast (Advisory #1, 2,...) for each time frame on Danielle. Positive bars show a position north of forecast, negative south of forecast. While the first forecast has verified pretty well, this shows subsequent forecasts not doing as well. Compare the errors to the cone radii, which are 36 n mi for 12 hours, 62 n mi for 24 hours, 85 n mi for 36 hours and 108 n mi for 48 hours. Many of the subsequent forecasts are outside of the cone.



That is nice...thanks for sharing.
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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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