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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1299. Max1023
Guys link to large loops, don't post them. It saves space and speeds the blog up.
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Quoting Max1023:
According to the CMISS blog the shear direction changed from easterly to northwesterly, Danielle's forward motion basically added 15 knots to the shear when it changed direction. Personally I believe that is what caused the weakening today.


I think U R right.
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Quoting originalLT:
Beautiful SRSO SAt. pic. Had never seen that before. Thanks post 1256.


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.

http://cimss.ssec.wisc.edu/goes/blog/wp-content/uploads/2010/08/100824_g15_vis_srso_2_anim.gif


Taken from Here.
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1293. Engine2
http://cimss.ssec.wisc.edu/goes/blog/wp-content/uploads/2010/08/100824_g15_vis_srso_2_anim.gif
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I guess I'm banned now
See you tomorrow
Happy hunting
.
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1287. Max1023
According to the CMISS blog the shear direction changed from easterly to northwesterly, Danielle's forward motion basically added 15 knots to the shear when it changed direction. Personally I believe that is what caused the weakening today.
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Sorry they had to remove post 1256, the Satellite pic. was beautiful, super clear.
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1285. xcool


18z
Member Since: September 26, 2009 Posts: 2 Comments: 15684
what is the 18Z GFS saying?

surprised no one has started posting it yet
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1283. xcool
SHORT TERM...
THE CANADIAN FRONT MOVES FURTHER EAST AND SOUTH...EVENTUALLY
COLLIDING AND MERGING WITH THE WESTWARD-MOVING GULF EASTERLY WAVE
NEAR 92W BY EARLY EVENING THURSDAY.

THE MERGED FRONT-EASTERLY WAVE CONTINUES ITS JOURNEY WESTWARD...
LANDFALLING ALONG THE TEXAS COAST BY EARLY EVENING FRIDAY.

A RAIN EVENT IS POSSIBLE OVER THE WEEKEND...ESPECIALLY ACROSS
SOUTHEAST TEXAS AND SOUTHWEST LOUISIANA. INCOMING CARIBBEAN AIR
WILL UPSLIDE THE MERGED FRONT-EASTERLY WAVE SYSTEM (WHICH SLOPES
WESTWARD TOWARD THE DRY AIR WITH HEIGHT). OVERRUNNING CLOUDS AND
RAIN ALONG WITH A FEW EMBEDDED THUNDERSTORMS MAY BE THE RESULT.





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.



.LONG TERM (THURSDAY THROUGH TUESDAY)...COLD FRONT WILL PUSH THROUGH
THE ENTIRE CWA AND INTO THE GULF OF MEXICO BY THURSDAY. TOOK OUT ALL
POPS ON THURSDAY AND THURSDAY NIGHT FOR LAND AREAS AS DEWPOINTS
SHOULD BE IN THE 60S FOR MOST AREAS AND MOISTURE WILL BE PUSHED INTO
THE GULF. THE FRONT WILL MERGE WITH AN INVERTED TROUGH ACROSS THE
CENTRAL/WESTERN GULF...AND AFTER THIS TIME THE FORECAST BECOMES VERY
COMPLICATED. MODELS DIFFER SIGNIFICANTLY WITH THE EVOLUTION OF THE
SYSTEM. THE NEWEST RUN OF THE ECMWF DEVELOPS A TROPICAL DEPRESSION
AND SHUNTS ALL THE PRECIP OFF TO THE NORTH OF THE AREA INTO EASTERN
TEXAS AND SOUTHERN LOUISIANA. THE GFS KEEPS THE SYSTEM MORE AS AN
INVERTED TROUGH AND WOULD BRING MODERATE TO HEAVY RAIN OVER THE
COASTAL PLAINS FOR THE WEEKEND AS THE SYSTEM MOVES ACROSS SOUTH
TEXAS. THE CANADIAN IS FAIRLY SIMILAR TO THE ECMWF IN DEVELOPMENT
AND STALLING THE SYSTEM OFF THE COAST BEFORE MOVING IT NORTH...WITH
NO RAIN FOR OUR AREA. BECAUSE OF THESE DIFFERENCES...DID NOT MAKE
TOO MANY CHANGES TO THE OVERALL EXTENDED FORECAST. HOWEVER...DID CUT
BACK POPS SLIGHTLY FOR THE WEEKEND. THE RAIN CHANCES FOR THE
BEGINNING OF NEXT WEEK WILL ALSO DEPEND ON WHAT HAPPENS WITH THE
SYSTEM IN THE GULF.
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Beautiful SRSO SAt. pic. Had never seen that before. Thanks post 1256.
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Danielle's not looking so anaemic. Starting to slowly build itself internally, as well.

May take the night at the very least, unless she goes on another growth spurt.

These kids.
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Quoting IKE:


Yeah...don't you know?
No.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
1278. IKE
Quoting MiamiHurricanes09:
Great JP?


Yeah...don't you know?
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1276. IKE
Quoting sporteguy03:

I hope not Ike no one needs these systems to affect them. I was surprised it weaken to a TS though that was surprising.


It looks like it's heading back to a hurricane soon.
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bouncin in for just a few...watching the second storm more so...have family coming from WV to Charleston, SC Labor day weekend...
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1274. Max1023
NVM problem at my end.
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Quoting xcool:


hmmmm...Close to home....looks like a good rain maker at the very least.
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Quoting IKE:


I'm so glad I have the great JP....er, 101, on ignore. Fire away!
Great JP?
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting Max1023:
1526: WHERE DID YOU GET THAT!!! It appears that the MLC of Danielle was decoupled to the east and is currently stacking itself as the convection overtakes the center. Overall looks like an intensifying system.


CIMSS Satellite Blog. Its pretty interesting, they update it every few days. And it always has something to do with satellite imagery.
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Quoting IKE:


That should start up after Danielle passes Bermuda. Buckle up...the westcasting and slamming into Florida could get hot and heavy.

I hope not Ike no one needs these systems to affect them. I was surprised it weaken to a TS though that was surprising.
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1268. IKE
And all I said was...

Quoting IKE:
If it follows the center of the track, the NHC has, Bermuda will be 150 miles west of where she goes. They'll survive.


I didn't say it was written in stone.
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Quoting SFlKatCane5:
hyperbole about the gulf oil spill has sunk the economy of the region. I fight regional hyperbole wherever I find it. because it is the right thing to do.

bermuda does fine in hurricanes.

visit bermuda and often as it is a most beautiful island in the gulf stream!
Umm, Bermuda is not in the Gulf Stream. And that is clear.

Clearly.......c,c,c,c,c,c,clearly.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
1266. Max1023
1526: WHERE DID YOU GET THAT!!! It appears that the MLC of Danielle was decoupled to the east and is currently stacking itself as the convection overtakes the center. Overall looks like an intensifying system.
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1265. Engine2
Quoting eliteforecaster:
The many faces of StormW

Image and video hosting by TinyPic

and new SRSO (Super Rapid Scan Operation of Danielle

SRSO looks like 2 separate circulations - is it not vertically stacked or center relocation? any takers?
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Quoting Hurricanes101:


atcf site update is in about 2 1/2 hours usually



cool
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1262. Sting13
Storm do you see the models shifting anymore west or is this about it, right now GFS puts Danielle just off the coast of nova scotia and the closer it gets to bermuda, the less time it has to turn out away from the maritimes.
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1259. xcool
Season total
Storm Type ACE (104 kt2)
01L (Alex) Operational 6.7825
03L (Bonnie) Operational 0.3675
04L (Colin) Operational 1.9450
06L (Danielle) Operational 3.435
Total 12.53
Member Since: September 26, 2009 Posts: 2 Comments: 15684
1258. Max1023
Danielle still heading at about 295 over 7 hours, maybe a bit of a westward jog in the last hour.
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Quoting Tazmanian:
we sould find out soon if we have TD 7 at the atcf site


atcf site update is in about 2 1/2 hours usually
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we sould find out soon if we have TD 7 at the atcf site
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1254. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Quoting Hurricanes101:
Quoting IKE:
If it follows the center of the track, the NHC has, Bermuda will be 150 miles west of where she goes. They'll survive.


Wow I was not aware that the center line was exactly where the storm was going to go?

You did see the part where the NHC said their track shifted a full 2 degrees further west by day 5 right?

But whatever you know where the storm is going to go right? How about you just tell us from now on and we ignore the NHC?
I was going to say something, but decided to stay silent, lol. Good post.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
1250. IKE
Quoting PRweathercenter:
the construction in bermuda is like puerto rico, everything is concrete, we are well prepared for storms


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.
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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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