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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Figured out how to do images :P

00z


06z


12z
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I personally don't believe Danielle will reach 20N until it reaches 55W.
Member Since: July 1, 2008 Posts: 13 Comments: 7390
Quoting btwntx08:
back in an hr
umm... what were those rules you posted? We'll miss you.

Danielle is bugging me, keep away from the east coast, start the turn already?
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Quoting slicknickel:
Let us not forget the significance of this date. Here in Miami we are observing the 18th anniversary of Hurricane Andrew, which changed the lives of so many people here.

A lot of us still divide our history in terms of pre or post Andrew.


Know how you feel. We also are looking at an anniversary soon. The Big K on the 29th. We divide our time line in before-Katrina and after-Katrina too. It's like PTSD, you have flashbacks.
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Quoting Relix:
Danielle is having heavy issues at the moment. She should fix herself soon but more weakening can cause westward shifts in track.
Also, like Masters mentioned, if it does weaken, then the one behind it may head more westerly due to less weakening of the rigde.
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either school let out early or some of you are home schooled
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Serious Flag: ON

Do any of yesterday's models have a storm around the Yucatan entering the Gulf any more?
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Quoting calder:
near 0% chance of Danielle affecting the US


I'm still evacuating to Toronto..
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HURRICANE DANIELLE DISCUSSION NUMBER 12
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL062010
1100 AM AST TUE AUG 24 2010

THE PERIOD OF RAPID INTENSIFICATION HAS ENDED WITH A THUD. THE
LOW-LEVEL CENTER OF DANIELLE HAS BECOME EXPOSED BETWEEN A RAGGED
CENTRAL DENSE OVERCAST TO ITS EAST...AND A BROKEN CONVECTIVE BAND
TO ITS WEST. ALL ALONG...MICROWAVE IMAGERY SINCE ABOUT 0300 UTC
SHOWED A DRY SLOT WRAPPING AROUND THE WESTERN AND SOUTHERN SIDE OF
THE CIRCULATION...AND AS A RESULT THE EYEWALL BECAME ERODED. DATA
T-NUMBERS HAVE FALLEN QUICKLY AND ARE NOW AS LOW AS T3.9 FROM THE
HURRICANE INTENSITY ESTIMATE...AN EXPERIMENTAL FORM OF THE UW-CIMSS
ADT. THE INITIAL INTENSITY IS LOWERED TO 70 KT AT THIS TIME...
WHICH COULD STILL BE GENEROUS. SHIPS GUIDANCE SHOWS WESTERLY TO
SOUTHWESTERLY SHEAR INCREASING TO BETWEEN 15 AND 20 KT OVER THE
NEXT 24 HOURS OR SO...AND IT IS UNCLEAR HOW WELL DANIELLE WILL BE
ABLE TO MIX OUT THE DRY AIR. ONLY SLOW STRENGTHENING IS INDICATED
IN THE OFFICIAL FORECAST...AND THE INTENSITY AT DAYS 4 AND 5 IS
HELD JUST BELOW MAJOR HURRICANE STRENGTH TO MAINTAIN SOME SORT OF
CONTINUITY...BUT THIS IS NOW ABOVE MANY OF THE INTENSITY MODELS.

MICROWAVE FIXES INDICATE THAT DANIELLE HAS BEEN MOVING QUICKLY WITH
AND A AN INITIAL MOTION ESTIMATE OF 290/17. THIS MOTION IS A
LITTLE TO THE LEFT OF THE FORECAST TRACK. LITTLE CHANGE IS
REQUIRED IN THE FORECAST...AND DANIELLE IS STILL EXPECTED TO TURN
TOWARD THE NORTHWEST THROUGH A WEAKNESS IN THE SUBTROPICAL RIDGE.
THE MODEL GUIDANCE REMAINS IN VERY GOOD AGREEMENT ON THIS SCENARIO.
THE OFFICIAL FORECAST TRACK LIES A LITTLE WEST OF THE PREVIOUS
FORECAST DURING THE NEXT 48 HOURS TO ACCOUNT FOR THE INITIAL MOTION
BUT THEN REMAINS CONSISTENT WITH THE EARLIER FORECASTS FOR DAYS 3
THROUGH 5. THIS SOLUTION IS VERY CLOSE TO THE MULTI-MODEL
CONSENSUS TVCN AND STILL A LITTLE LEFT OF THE GFS...GFDL...AND
HWRF...WHICH SEAMS REASONABLE GIVEN THE CONTINUED LEFT-OF-TRACK
MOTION.

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There is a decent amount of really dry air entering the northern Gulf from the Conus. Its heading south and spreading out with time.

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Sarcasm flag: ON

Are you kidding me? this blog knows more than the NHC....
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Quoting KerryInNOLA:
Every freaking storm that comes along has you guys playing scientist and predicting contrary to the pros. Just sit back and leave the driving to the NHC. Oh, and wipe the egg off your face, it might have salmonella

But that's the point of a blog like this. Right or wrong, us arm chair mets like to predict. Why ya care?
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Morning all. Long time no blog, I see the ATL has turn on now that I have had my net turned back on after moving.
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A lot of "hobbyists" keep saying it will go further west than what the NHC says. Have you ever seen the inside of the Center? It is 23rd century. They are the pros with the degrees, brains and large salaries to boot. They are doing their jobs giving us cutting edge forecasts. We are allowed to discuss and debate, this is America, but remember they wear the pants.

They are very capable, no doubt. They are also a government operated facility, part of a government agency. If you don't think this has an impact on their positions and predictions, perhaps you have never had to interact with a federal agency.
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Quoting RitaEvac:
Serious flag: ON

Last night on National Geographic, they had a 2 hr documentary of people who took videos during Katrina and after. Was awesome, showed the real stuff of what it looked like.
cool, i'd be interested in seeing that
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Doesn't Danielle have to slow down to make that turn, the NHC is talking about? If Danielle weakens could that change her track? Also if she misses the two troughs then some folks in her path are doomed.jmo
Member Since: July 8, 2008 Posts: 0 Comments: 158
Serious flag: ON

Last night on National Geographic, they had a 2 hr documentary of people who took videos during Katrina and after. Was awesome, showed the real stuff of what it looked like.
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172. beell
Meanwhile...Danielle at 17N.
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Quoting btwntx08:

???
he's joking geeezzz
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Sarcasm flag: ON
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ok lookin on the vis sat loop danielle has either rapidly moved west causing the COC to look disrupted or Danielle has rapidly weaken to a weak TS or strong TD with a bad COC no eye
Member Since: June 13, 2009 Posts: 2 Comments: 12035
near 0% chance of Danielle affecting the US
Member Since: July 26, 2006 Posts: 0 Comments: 419
158. Relix
Danielle is having heavy issues at the moment. She should fix herself soon but more weakening can cause westward shifts in track.
Member Since: August 3, 2006 Posts: 0 Comments: 2723
This is just a blip with Danielle, there is absolutely nothing impeding her from further strenghtening, have a look at the SAL, shear and SST maps.
Member Since: July 26, 2006 Posts: 0 Comments: 419
Quoting IKE:
Does this song apply>>>>????



Oh, I don't think this storm is anywhere near done or dead.
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She is falling apart cause she doesnt want to go north she wants to visit the GOM
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the weeker daniel stays the more west she will a go
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Danielle is falling apart. This could provoke changes on it's trajectory???
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i'm thinking if danielle weakens more then future TD 7 may have more of a chance to hit the mainland....
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Hi all, just thought i'd submit something for once instead of asking questions: Maybe someone can tell me how to post images because it doesnt seem to be working, thanks :)

00z
http://raleighwx.easternuswx.com/models/atcf/00zatcflateinvest1.gif

06z
http://raleighwx.easternuswx.com/models/atcf/06zatcflateinvest1.gif

12z
http://raleighwx.easternuswx.com/models/atcf/12zatcfearlyinvest1best.gif
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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.