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:


Ok...Flood!



Can I be part of your entourage? LOL
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I agree. Storm is a great and nice guy who answers questions in a very nice manner. It is very kind of him to take lots of time out during his busy day to educate us.

I love this blog because of his professionalism and expertise. Great job Storm!
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Quoting StormW:


Ok...Flood!



Everyone is a friend of Storm except those who are really ignorant.
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You can definitely tell it's advisory time...the blog slowed down considerably. LOL!
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Dr Masters isn't going on holiday again during the season?
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1040. CJ5
Quoting mojofearless:


Someone's bashing StormW? How uncouth! Sign me up for the Poof Brigade! And no Storm, you do NOT come across as a grumpy old man. Not at all.


What? He has been chained to the Coast Guard for 20+ years, or course he is old and grumpy!
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Quoting StormW:


I'm not expecting that until the upper level anticyclone gets re-established over the center, and becomes more symmetric. May help her to fight back against the dry air.

Ok. Thanks!!!
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Quoting betapaul:
I read this blog daily and I don't THINK I've ever posted...

After hitting refresh about 3,293 times today, I realized how it could be useful to have a chatroom here...

That being said, when I logged in I saw a "Start a Weather Chat" button. THEN I wondered, "Well if someone like, I dunno, STORMW had a chat, I would like to join it."

I didn't see this as an option. Am I missing something or is the comments section THE place to be?

The chat room is not safe to enter. Take this blog at its worst and multiply it by 100.
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1037. IKE
Quoting angiest:


They may have been in the cone, but the cone is not the location they forecast to get hit. They are being honest that they may be off by that much. And although people should always pay attention to where a storm could be, the average person is likely only to look at the thin black line. Local news media typically do not help.


Bastardi forecast a Florida panhandle hit on Florida Network News...I heard him on the local AM station say it. Then he switched to LA. and said on FOX news that that's where he had been forecasting it to hit all along. A slight fib Joe.
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People are heating against Storm? Seriously?

Not much to say about Danielle that hasn't been said. I don't see Danielle strengthening too much, especially as it begins to recurve into colder waters. What I want to see is how Danielle effects future-Earl. Stronger Danielle that allows for future-Earl to play follow the leader? Or does future-Earl head W/WNW for the next few days?
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1035. breald
Quoting StormW:


Ok...Flood!



me too..lol
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On a serious note, seeing some convection around Danielle firing back up so she is fighting that drier air.
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1032. angiest
Quoting mojofearless:


I'd say the August 25th forecast for Katrina was pretty off-base. It predicted an eastern Florida panhandle hit.


They may have been in the cone, but the cone is not the location they forecast to get hit. They are being honest that they may be off by that much. And although people should always pay attention to where a storm could be, the average person is likely only to look at the thin black line. Local news media typically do not help.
Member Since: Posts: Comments:
I read this blog daily and I don't THINK I've ever posted...

After hitting refresh about 3,293 times today, I realized how it could be useful to have a chatroom here...

That being said, when I logged in I saw a "Start a Weather Chat" button. THEN I wondered, "Well if someone like, I dunno, STORMW had a chat, I would like to join it."

I didn't see this as an option. Am I missing something or is the comments section THE place to be?
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1029. KEEPEROFTHEGATE (Mod)
06L/H/D/C1
CONVECTIVE REFIRE DETECTED
Member Since: July 15, 2006 Posts: 171 Comments: 53809
1027. angiest
Quoting F4PHANTOM:
NWS HOUSTON / GALVESTON @ 2:50PM A BIT OF A PATTERN CHANGE OVER THE WEEKEND AS AN UPPER LEVEL RIDGE
SHIFTS TO THE NORTHEAST AND A RATHER POTENT TROUGH DEVELOPS OVER
THE WESTERN U.S.. THIS WILL ALLOW A DEEP FETCH OF TROPICAL
MOISTURE TO TAKE AIM ON THE TEXAS COAST. AN INVERTED TROUGH OF LOW
PRESSURE WILL DEVELOP AT THE SURFACE AND ALSO MOVE SLOWLY INLAND
SAT/SUN. THE ECMWF...GFS AND CAN SHOW THE SFC TROUGH AND ASSOICATED
WEAKNESS ALOFT. LONG RANGE MODELS DIFFER SIGNIFICANTLY WITH THE
PLACEMENT OF THE HEAVIEST PRECIPITATION. THE 12Z ECMWF/CAN ARE IN
GOOD AGREEMENT OF DISPLACING THE PRECIP TOWARD LOUISIANA...WHILE
THE GFS PLACES THE GREATEST RAINFALL ON THE TEXAS COAST. THE
ECMWF/CAN HAVE NOT SHOWN MUCH CONSISTENCY AND PREFER THE MORE
STABLE GFS. THE GFS SHOWS PW VALUES OF 2.4 TO 2.6 INCHES AND A
NEARLY STATIONARY BOUNDARY ALONG THR COAST. IF THE GFS PANS OUT...
HEAVY RAIN WILL BE POSSIBLE ALONG THE COAST WITH A SHARP QPF
GRADIENT. COULD SEE EXCESSIVE RAIN AT THE COAST AND LESS THAN AN
INCH OF RAIN WELL INLAND. WHICHEVER SUITE OF MODELS IS
CORRECT...AT LEAST SCATTERED SHOWERS SHOULD OCCUR WITH MORE CLOUDS
AND LOWER HEIGHTS TRANSLATING INTO LOWER TEMPERATURES. 43
The rain will be wecomed


Well, we are leaving the hottest time of the year (that is, average highs should be easing back from ~94 degrees to ~93 degrees) and the long heat spells should be coming to an end soon anyway
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Quoting samhou67:
I'm new to Weather Underground...Does anyone see a storm threat to the Texas Gulf Coast in the next two weeks?


Not much, no...slight chance of some development after the low drops off into the GOM in two days, but that's a low percentage chance
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Yep, StormW fan here myself. Pretty much seems like everything he says is what happens.
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Quoting mojofearless:


I'd say the August 25th forecast for Katrina was pretty off-base. It predicted an eastern Florida panhandle hit.


NO was in the cone
Member Since: September 6, 2007 Posts: 0 Comments: 6485
Quoting Floodman:


Wow, Storm! You appear to have a few friends here...add me to the list, by the way...

Yeah same here!
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Storm, when is Danielle expected to get some more convection on its northwest side?
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I'm new to Weather Underground...Does anyone see a storm threat to the Texas Gulf Coast in the next two weeks?
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Quoting wjdow:
quoting... 'but any time the models make a massive mistake in unison, the NHC is right there making it with them, and that is why they aren't as good as they could be if they dared to defy the models.'

So when in the last couple years, say, has NHC made a massive mistake? I don't remember any. There's a potential for over-reliance on models to lead to a mistake, but I don;t remember it actually happening, at least not recently.


I'd say the August 25th forecast for Katrina was pretty off-base. It predicted an eastern Florida panhandle hit.
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Quoting StormW:


Thank you, sir!


Wow, Storm! You appear to have a few friends here...add me to the list, by the way...
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Storm,

Wow, bromance caster?
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NGP actually showing a direct landfall on Bermuda then hinting at turning back towards VA which to me seems really strange.

GFS is starting to bring it closer to Bermuda.

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1014. jonelu
When I look at the North Atlantic water vapor and the North Atlantic Dvorak is almost like there is a arrow pointing at Bermuda.
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THIS DRY AIR MASS WILL PREVAIL OVER THE LOCAL FORECAST AREA THROUGH
LATE WEDNESDAY NIGHT AS MOISTURE ASSOCIATED TO DANILLE BEGINS TO
MOVE TOWARD THE LOCAL FORECAST AREA...SLIGHTLY INCREASING THE
SHOWER COVERAGE. A MUCH UNSTABLE ATMOSPHERE IS EXPECTED TO PREVAIL
OVER THE AREA AS THE TUTT ALOFT ESTABLISHES TO THE NORTH OF THE
ISLANDS AND MID LEVEL RIDGE BEGINS TO ERODE/WEAKEN.

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96L should be a tropical depression by the days' end. The circulation looks plenty well-defined to me.

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Storm...YOU are the reason I come to the blog... shown me more than I can remember...Good work Senior Chief. Thanks
Bob
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Quoting atl134:
So looking at the 12z model runs, I noticed that the NOGAPS model has a disturbingly high westward change compared to previous runs. I guess it doesn't seem to have the trough curving Danielle out as much as the others. I see all the other models (that I know of) have Danielle farther east but while I was ready to rule out US landfall yesterday, I'm guessing such a statement is premature (even if it's only order 5-10% odds).

http://www.meteo.psu.edu/~gadomski/NGPTROPATL_12z/nogapsloop.html


to, close for comfort...
Member Since: September 6, 2007 Posts: 0 Comments: 6485
1005. atl134
So looking at the 12z model runs, I noticed that the NOGAPS model has a disturbingly high westward change compared to previous runs. I guess it doesn't seem to have the trough curving Danielle out as much as the others. I see all the other models (that I know of) have Danielle farther east but while I was ready to rule out US landfall yesterday, I'm guessing such a statement is premature (even if it's only order 5-10% odds).

http://www.meteo.psu.edu/~gadomski/NGPTROPATL_12z/nogapsloop.html
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Quoting clwstmchasr:


He was talking about 96L. He said that he thought that the NHC would upgrade it to a depression at 5:00. He then went on to say that maybe not because it is so difficult figuring out the NHC when they classify storms because it sometimes does make sense.


im tired of it to be honest....
Member Since: September 6, 2007 Posts: 0 Comments: 6485
The CIMSS PREDICT site suggests that 20-30 knots of wind shear are affecting Danielle with an isolated spot of 40 knots near the northern quadrant. However, anticyclonic flow dominates most of the system since this graph shows the anticyclone being much closer to the circulation.

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Just watch the coc of Danielle relocate under the biggest blow up convection further west and south again, jmo.
Member Since: April 29, 2007 Posts: 0 Comments: 7862

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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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