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 BobinTampa:


the writer of this blog has a Ph.D. Not good enough??


Yeah, seems a lot of rudeness going on in here today, and a lot of fluffing feathers.
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Quoting StormW:
HURRICANE DANIELLE SYNOPSIS AUGUST 24, 2010 ISSUED 11:50 A.M.


Thanks Storm as always!!!
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245. RMCF
Quoting StormW:
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.

Oh geez...here we go with the Ph.d stuff again...may I gag now or later?

Yeah and if a cat 4 makes landfall FEMA will be there in shiny armor to fix everything LOL.
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Danielle is stripping fast, where going to be seeing some skin, if she doesnt get her act together.

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241. Skyepony (Mod)
Quoting hurricanejunky:
Something trying to form along that frontal boundary in the GOM?


It feels like it here. Yesterday the wind, ring around the moon lastnight. Today~ overcast & the windows are still fogged up. FL should disrupt it but still a good chance of some weather dragging up the east coast the next few days. I think how bad only depends on if it drags the coast or gets off shore a little where the east coast misses out. The way it's lingering in the gulf I'm leaning toward dragging up the coast.
Member Since: August 10, 2005 Posts: 162 Comments: 37831
Hi Everybody...off to run out into rotten weather. IRLoop
But first,

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239. SLU
815UTC




1545UTC

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Quoting StormW:
HURRICANE DANIELLE SYNOPSIS AUGUST 24, 2010 ISSUED 11:50 A.M.


Hello, nice update thx StormW,

just a question What do you think is the possible track forecast for Danielle?
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Quoting StormW:
HURRICANE DANIELLE SYNOPSIS AUGUST 24, 2010 ISSUED 11:50 A.M.


Thanks Storm - will be keeping an eye on the GOM. Do you think this would affect TX if it was to develop into anything?
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Quoting StormW:
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.

Oh geez...here we go with the Ph.d stuff again...may I gag now or later?


the writer of this blog has a Ph.D. Not good enough??
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Something trying to form along that frontal boundary in the GOM?
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Quoting StormW:
HURRICANE DANIELLE SYNOPSIS AUGUST 24, 2010 ISSUED 11:50 A.M.


Nice synopsis, thanks.
Member Since: August 22, 2010 Posts: 0 Comments: 652
Quoting clwstmchasr:
206. StormChaser81 11:48 AM EDT on August 24, 2010 Hide this comment.

Quoting clwstmchasr:


Dry air??????



Water Vapor Imagery

That dry air covers about 20% of the GOM.
Yea but the area is growing in size as it pushes further south. hard for something to develop until the environment becomes a little more favorable.
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I posted this on the previous blog but it's a rather historical day so...

Today marks the 18th anniversary of one of only 3 Cat 5 hurricanes to hit the US - Hurricane Andrew. Do you remember where you were on this day in 1992? I do. Hunkered down, waiting for Andrew to pass over us in Fort Myers. We take a trip back to that fateful day on August 24th, 1992 when Hurricane Andrew terrorized the Miami/Dade county region:

Hurricane Andrew - Path Of Terror
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Quoting StormW:
HURRICANE DANIELLE SYNOPSIS AUGUST 24, 2010 ISSUED 11:50 A.M.



StormW, Good Morning, I know your busy with a lot of questions but I am trying to understand this a little. Here's my ? if Danielle stays low in strength does that mean she could go more west and miss the trough, I mean the trough wouldn't influence her if she was little. Is that right? Then pre Earl could miss the trough to if he stays low in strength. You know I'm not a wishcaster or nothing like that just trying to wrap my head around it and understand.
Thanks for all you do,
sheri
Member Since: August 24, 2006 Posts: 21 Comments: 3676
Quoting clwstmchasr:


Dry air??????



Reread his post..he is talking big picture...
the overall MJO pattern is in dry,sinking air
phase...the wet weather you guys are seeing is
a localized event due to a frontal zone..BTW we
have the dryest air I have seen since spring
right now in SE Louisiana as we are behind the frontal zone...pattern is due to change late this week with High Pressure pushing boundary back North...
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Quoting clwstmchasr:
206. StormChaser81 11:48 AM EDT on August 24, 2010 Hide this comment.

Quoting clwstmchasr:


Dry air??????



Water Vapor Imagery

That dry air covers about 20% of the GOM.


Regardless it will not help any thing trying to spin up in the GOM.

It is also trying to move more south and that 20% is growing slowly.
Water Vapor Loop
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Quoting Michaelkaii10:


Why are you Talking to Yourself??


post 201

he forgot what id he had signed on with.
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219. Jax82
Hmmm, looking at the WV loop, is the trof split complete? I see a break right NE of FL.
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Quoting catastropheadjuster:


divdog, I have watched him on here and he bull craps and says stuff about a lot of folks on here. Just start trouble and to get attention. He really never adds nothing to the blog except drama.
sheri
Quoting catastropheadjuster:


divdog, I have watched him on here and he bull craps and says stuff about a lot of folks on here. Just start trouble and to get attention. He really never adds nothing to the blog except drama.
sheri
Yea I keep hoping some of the yougsters will learn and change their ways but i guess that is just a dream. The blog was less polluted even just a year ago. I don't put many on ignore but may have to start adding more so we can have good discussions in here and not have to see so much trash posted on the blog.
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217. IKE
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12Z GFS so far right on my forecast.. so far.
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One bad consequence of recurving storms is that the eastern caribbean may have a drough!
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Quoting reedzone:
I personally don't believe Danielle will reach 20N until it reaches 55W.


On its current track it should be at 20 or pass it by 51 or 52 - of course unless something changes,
Member Since: August 22, 2010 Posts: 0 Comments: 652
Where's ol Patrap at lately
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Quoting clwstmchasr:


Dry air??????



Water Vapor Imagery
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Link

GFS out 18hrs
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Quoting MrNatural:
It looks like the dry air to the west and east are contributing to the raggedness of Danielle(D). I would like someone to explain to me why so many models are expecting Danielle to start the hard right turn so soon. As I review the water vapor imagery from the Tropical Atlantic, it appears that Danielle is still under the control of the ridge to it's NW. If that's the case, what are the steering mechanisms that are going to swing it out of it's current track for at least 12 to 18 hours?


It is the trough of low pressure over the US East Coast that will turn it. The trough is moving east.. Danielle is moving west. The trough is a deep layer(means it goes through many layers of the atmosphere) low pressure system which has tow means of influencing the track of D.
ONE
Hurricanes want to go NORTH all by themselves due to the coriolis effect being stronger on their North side. Since the trough causes reduced pressure and makes the ridge retreat back east it will let D go north
TWO( the big one)
The counter clockwise circulation of the trough and it's low pressure will suck/pull D north.

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203. IKE
Hope Danielle spares Bermuda, otherwise she could be their vacationers dreadlock holiday.
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Quoting SFlKatCane5:


you da man! now bugger off!

Goodbye
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Quoting jasoniscoolman2010x:
ITS STILL WEAKENS JASON LOOK LIKE A TROPICAL STORM NOW.


Why are you Talking to Yourself??
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Figured out how to do images :P

00z


06z


12z
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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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