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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1098. IKE
Quoting barotropic:


to tell the truth, I was surprised at a couple who did doubt your cords....


I didn't.

Moving right on the earlier forecast track.

Nice job NHC!
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1095. xcool
she getting close to 50w
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Hi StormW,
I'm a lurker here but wanted to say I look for your comments and respect your analysis tremendously.
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OUCH!!! wow look at the new track
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Quoting reedzone:
Okay everyone, ready for the shift?
From the discussion:

DANIELLE IS STILL MOVING QUICKLY WITH AN INITIAL MOTION OF 295/16.
THE TRACK GUIDANCE INDICATES THAT THE CYCLONE SHOULD BEGIN TO SLOW
DOWN SOON AND TURN TOWARD THE NORTHWEST WITHIN THE NEXT 24 HOURS AS
IT MOVES INTO A WEAKNESS IN THE SUBTROPICAL RIDGE. THE MODELS HAVE
SHIFTED SIGNIFICANTLY TO THE WEST...HOWEVER...AND THE DAY 5
OFFICIAL FORECAST POSITION ENDS UP BEING 2 DEGREES FARTHER WEST
THAN IN THE PREVIOUS FORECAST. THIS NEW FORECAST IS STILL TO THE
RIGHT OF THE GFDL AND HWRF MODELS...AND IT LIES CLOSE TO THE MODEL
CONSENSUS OUT OF RESPECT FOR THE SHARPER-TURNING ECMWF.
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Quoting VAbeachhurricanes:


NO was in the cone


The blog keeps eating this post.
Anyway - no, New Orleans was not in the cone on the Thursday before Katrina.
Link
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1090. xcool
btwntx08 haha
Member Since: September 26, 2009 Posts: 2 Comments: 15684
1089. angiest
I'll be uploading a new comparison of Ike's track and Danielle's shortly.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
1085. xcool
NORTHWEST in about 48hrs jmo maybe
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Quoting btwntx08:
sorry but im older and have better i sight and to it was 17.3n


Its not that important anyway...no biggie at all
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Quoting btwntx08:
sorry but im older and have better i sight and to it was 17.3n
LOL, seriously? I thought as you got older your eye sight worsens. Anyways, I thought you were saying 17.0N, what happened to that?
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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 chat room 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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Okay everyone, ready for the shift?
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1080. xcool
btwntx08 you young .not older.lol
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Quoting Floodman:


The thing to remember about the GOM is that things can happen very fast...remember Humberto? It's a TD, no I mean TS no I mean a CAT1...LOL


If it wasn't clear, I meant my company subscribes to Impact, not that I work there. LOL
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Storm,

quick question for you. sorry to ask you this again. am not sure if you saw the question or I did not see it at the bottom.

What is your take in the models for 96L shifting signifiacantly westward?

Do you see the high getting stronger and steering future Earl towards CONUS? I know you do not go by the models only, but just wondering

Also,on a side note, I am getting really curious about how September is shaping for landfalls. Thanks as always Storm for your insight!
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1077. xcool
angiest yup
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Quoting StormW:


LMAO!

How's the back doing?


Good, for the most part; I really only hurt when I'm low on sleep or the weather is changing; oddly, I couldn't get to sleep last night and it's been trying to rain all day...what's that you say about karma?


LOL
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Quoting eliteforecaster:
Does anybody want a ton of general weather links?

Cuz I got a ---- load on my computer.


Anybody at all?

I got all that you could ever need.
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1072. angiest
Quoting MiamiHurricanes09:
...DANIELLE WEAKENS TO A TROPICAL STORM...EXPECTED TO BE TEMPORARY...

5:00 PM AST Tue Aug 24
Location: 17.5°N 48.2°W
Max sustained: 70 mph
Moving: WNW at 18 mph
Min pressure: 993 mb


Still say WNW. Didn't last night's discussions call for the NW turn to happen about .... now?
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting StormW:


And salty.


You know on land we have soap and fresh water for that. ;)
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Quoting jason2010xxxx:
SOME MODELES BACK TO THE WEST


I thought the NGP was turning it back to VA. I noticed that GFDL,GFS,and ECMWF was still recurving Danielle prior to Bermuda but its also possible that those model runs have not updated yet...nice pick up Jason.
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Quoting IKE:
.DANIELLE WEAKENS TO A TROPICAL STORM...EXPECTED TO BE TEMPORARY...
5:00 PM AST Tue Aug 24
Location: 17.5°N 48.2°W
Max sustained: 70 mph
Moving: WNW at 18 mph
Min pressure: 993 mb


Now...who doubted me on the coordinates?

Mellow out IKE:)


to tell the truth, I was surprised at a couple who did doubt your cords....
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Quoting IKE:
.DANIELLE WEAKENS TO A TROPICAL STORM...EXPECTED TO BE TEMPORARY...
5:00 PM AST Tue Aug 24
Location: 17.5°N 48.2°W
Max sustained: 70 mph
Moving: WNW at 18 mph
Min pressure: 993 mb


Now...who doubted me on the coordinates?

Mellow out IKE:)
Lol. What were you're coordinates? I had it at 17.4N 47.9W...turns out I was to the south and west of the circulation.

Definitely didn't see it near 17.0N as some were stating.
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Quoting dan77539:


Our company's weather service (Impact) pretty much agrees with you. Low percentage chance of a TS this weekend from what's in the Gulf right now. If the models are improving their initiatation of systems, we'll see how they do here.


The thing to remember about the GOM is that things can happen very fast...remember Humberto? It's a TD, no I mean TS no I mean a CAT1...LOL
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Quoting btwntx08:


btwn, I have no idea how to analyze this GOM scene. What's going on here?
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1064. KEEPEROFTHEGATE (Mod)
06L/TS/D/CX
MARK
16.88N/47.99W

Member Since: July 15, 2006 Posts: 174 Comments: 54429
Quoting Floodman:


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


Our company's weather service (Impact) pretty much agrees with you. Low percentage chance of a TS this weekend from what's in the Gulf right now. If the models are improving their initiatation of systems, we'll see how they do here.
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1059. breald
Quoting IKE:


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.


Joe B One Kenobi is such a politician.
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Quoting btwntx08:



some in sure is trying too cook in the gulf
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...DANIELLE WEAKENS TO A TROPICAL STORM...EXPECTED TO BE TEMPORARY...
Member Since: Posts: Comments:
ZCZC MIATCDAT1 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM DANIELLE DISCUSSION NUMBER 13
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL062010
500 PM AST TUE AUG 24 2010

WITH JUST A LITTLE BIT OF UNEXPECTED WESTERLY SHEAR...DANIELLE HAS
UNRAVELED DURING THE DAY. THE LOW-LEVEL CENTER HAS OCCASIONALLY
BEEN EXPOSED TO THE WEST OF A DISORGANIZED CLUSTER OF DEEP
CONVECTION...AND THE DVORAK ESTIMATES HAVE DECREASED ACCORDINGLY.
FINAL-T AND CI ESTIMATES FROM THE UW-CIMSS ADT ARE NOW NEAR
T3.5/4.5 AND SUPPORT DOWNGRADING DANIELLE TO A 60-KT TROPICAL
STORM. WITHOUT SUFFICIENT OBSERVATIONAL DATA IN THE CYCLONE
ENVIRONMENT...OPERATIONALLY WE CAN NOT SPECULATE WITH CERTAINTY WHY
DANIELLE WEAKENED TODAY.

ENVIRONMENTAL CONDITIONS SUPPORT DANIELLE RE-INTENSIFYING INTO A
HURRICANE SOON...AND THAT IS REFLECTED IN THE OFFICIAL FORECAST.
THE INTENSITY GUIDANCE...EXCEPT FOR THE GFDL WHICH SHOWS DANIELLE
BECOMING AN INTENSE HURRICANE IN ABOUT 4 DAYS...INDICATES GRADUAL
STRENGTHENING DURING THE FORECAST PERIOD. THE NEW OFFICIAL
FORECAST IS HIGHER THAN THE STATISTICAL MODELS...WHICH ARE STRONGLY
AFFECTED BY PERSISTENCE...BUT IT REMAINS MUCH LOWER THAN THE GFDL
AT THIS TIME.

DANIELLE IS STILL MOVING QUICKLY WITH AN INITIAL MOTION OF 295/16.
THE TRACK GUIDANCE INDICATES THAT THE CYCLONE SHOULD BEGIN TO SLOW
DOWN SOON AND TURN TOWARD THE NORTHWEST WITHIN THE NEXT 24 HOURS AS
IT MOVES INTO A WEAKNESS IN THE SUBTROPICAL RIDGE. THE MODELS HAVE
SHIFTED SIGNIFICANTLY TO THE WEST...HOWEVER...AND THE DAY 5
OFFICIAL FORECAST POSITION ENDS UP BEING 2 DEGREES FARTHER WEST
THAN IN THE PREVIOUS FORECAST. THIS NEW FORECAST IS STILL TO THE
RIGHT OF THE GFDL AND HWRF MODELS...AND IT LIES CLOSE TO THE MODEL
CONSENSUS OUT OF RESPECT FOR THE SHARPER-TURNING ECMWF.
Member Since: Posts: Comments:
1054. IKE
.DANIELLE WEAKENS TO A TROPICAL STORM...EXPECTED TO BE TEMPORARY...
5:00 PM AST Tue Aug 24
Location: 17.5°N 48.2°W
Max sustained: 70 mph
Moving: WNW at 18 mph
Min pressure: 993 mb


Now...who doubted me on the coordinates?

Mellow out IKE:)
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Danielle down to TS status once again.
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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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