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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2399. xcool
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2398. xcool
Caribbean keep eye on 96L SOON TO BE Earl
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Good night, everyone.

Not only does it look like a busy rest of the week.....but a VERY busy rest of the season.
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2384. KEEPEROFTHEGATE

KOG ... these bright-red-blood images give me the creeps ... they always look like a colonoscopy gone really bad. Just sayin.
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Quoting neonlazer:


What site are you getting these update to date models from? I have a like four sites..but all are java loops. lol
You should be able to look at loops or individual images on most of those sites...

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2393. hydrus
Quoting KEEPEROFTHEGATE:
That wave over Africa dwarfs 96L.
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2392. xcool
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Alright I just took a look at the 18Z GFS. I'm sure yall are already discussing it... but what is going on?! It has Danielle heading straight for the northeast now at day 7. Has Levi or Storm touched on this?
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Stalling out over bermuda for 24 hours would be a worst case scenario...
Member Since: September 6, 2007 Posts: 0 Comments: 6061
Well, it's east of 18z, but Earl and Fiona look impressive.
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2388. xcool
neonlazer


Link
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2387. xcool
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Quoting xcool:


What site are you getting these update to date models from? I have a like four sites..but all are java loops. lol
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2385. smuldy
Quoting xcool:
lol the high pressure completely bridges the gap on this run? lol
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2384. KEEPEROFTHEGATE (Mod)
Member Since: July 15, 2006 Posts: 169 Comments: 53296
2383. xcool



120hrs she not move much.
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I would definetly like to see what the NHC has on Danielle on Wednesday and soon to be TS Earl. Should be an interesting week.
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2381. xcool
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2380. Relix
She's only about 10-15 miles SW of her next forecast point. Due west movement is caused by the moving of convection and a bad visible. Not even shortwave helps. Using Visible, Rainbow and Shortwave you can notice she's moving around 275-280. She should miss her next point by about 25-30 miles. Let's see if this lasts all night like last night. Off to bed then!
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2379. xcool
crazy crazy week a head..
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Bend west beginning at hour 129...
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2377. scott39
Quoting xcool:

I think those will shift W again.
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2376. 7544
she kkeeps moving west we might even see a shift in the models to further south at this point stay tuned
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Quoting philliesrock:
GFS is actually a little farther west at 114.


That huge high is building in on top of it to... plus that trough in KAN isnt budging eastward
Member Since: September 6, 2007 Posts: 0 Comments: 6061
2374. xcool

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2373. hydrus
Quoting 7544:
yeap shes moving west again
Danielle wants some New England Clam Chowder...jk...
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Quoting ChrisDcat5Storm:



mabey 3 beers is to much but i just dont see the west movement its right on the forecast point
Not 3 beers my friend you're just the odd man out tonight , most on the blog are seeing a clear westward movement, of course you see what you see so I can't argue about that, btw they change the forecast points with each update.
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GFS is actually a little farther west at 114.
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Quoting KEEPEROFTHEGATE:
06L/H/D/C1
MARK
19.01N/50.25W

More like 18.5N on 06L
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2369. xcool


96l bigg hurricane .
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Quoting philliesrock:
Can you guys stop posting that loop of 1-minute updates, and start linking it instead? It's taking a few minutes to load and slowing down my internet connection.
Do what I do, hit it with a - and it goes away. Some people don't get it that the whole world is not suburbia.
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Quoting hunkerdown:
they blew it in the bottom of the 14th...and Oswalt in left


dang shame.... ummmm and can someone tell the GFS that its close enough to my house, it can turn now?
Member Since: September 6, 2007 Posts: 0 Comments: 6061
GFS has Bermuda in its crosshairs again
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Quoting xcool:


Fish train? lol Hope so!
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Quoting philliesrock:

I'm watching the game and looking at the GFS at the same time. :D
they blew it in the bottom of the 14th...and Oswalt in left
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2363. xcool
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2362. Relix
Every night she does the same! XD! At this point it's just tropical interest for me as I am watching from PR. Love watching them. 96L and our future invest are now in my eyes =)
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2361. xcool


96L FAR SOUTH ..
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Quoting xcool:


3 STORMS.
From there on in it looks like a race between Danielle and the trough at that point around the KANSAS-NEBRASKA area. We'll see.
.
For right now, I'm making a run for the border. Can I get anything for anybody?
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2359. hydrus
Quoting xcool:


3 STORMS.
It will look like 1995 if that model pans out. 3 named storms in the Atlantic simultaneously before the end of August?...I believe it is likely to happen.jmo
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2358. Relix
Quoting serialteg:
good evenin fellowes... keeperofthegate... brethren and caribbean dwellers alike. looking for some good surf to hit the islands.


Get ready for the surf. XD! You've been waiting for it for eternity now haha
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HurricaneDanielle's heading has turned westward to 1.7degrees north of WestNorthWest
from the previous heading of 2.5degrees north of WestNorthWest

24Aug - 03amGMT - 15.6n43.2w - - 85mph . . . . . 982mb - NHC.Adv.10
HurricaneDanielle becomes Cat.2
24Aug - 06amGMT - 15.7n44.0w - - 85knots . . . . 973mb - NHC-ATCF
24Aug - 09amGMT - 15.9n44.6w - - 100mph . _ . 973mb - NHC.Adv.11
24Aug - 12pmGMT - 16.1n45.8w - - 75knots . . . . 983mb - NHC-ATCF
24Aug - 03pmGMT - 16.6n46.5w - - 80mph . . . . . 985mb - NHC.Adv.12
24Aug - 06pmGMT - 17.1n47.5w - - 65knots . . . . 990mb - NHC-ATCF
H.Danielle becomes TS.Danielle
24Aug - 09pmGMT - 17.5n48.2w - - 70mph . . . . . 993mb - NHC.Adv.13
25Aug - 12amGMT - 17.9n49.1w - - 65knots . . . . 990mb - NHC-ATCF
TS.Danielle becomes H.Danielle again
25Aug - 03amGMT - 18.2n49.8w - - 75mph . . . . . 990mb - NHC.Adv.14

_ _ _ ~60.9knots=70mph _ _ _ 65knots=~74.8mph _ _ _ ~65.2knots=75mph
NHC rounds windspeeds to the nearest 5mph or to the nearest 5knots

Copy&paste 16.6n46.5w-17.1n47.5w, 17.1n47.5w-17.5n48.2w, 17.5n48.2w-17.9n49.1w, 17.9n49.1w-18.2n49.8w, bda, jax into the GreatCircleMapper for a look at the last 12hours.
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2356. xcool
I NEED ECMWF model support too.
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Quoting stormpetrol:
I have the coc at 18N/49.9W, westward movement, maybe a tad wobble south of due west



mabey 3 beers is to much but i just dont see the west movement its right on the forecast point
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2354. 7544
yeap shes moving west again
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2353. scott39
Quoting nolacane2009:


Scott,

Your opinion what do you think is going on?
Im not a Met but I will take a shot. I think she is going faster than forecasted. She also weakened when not expected to. The first trough bypassed her and had little effect on steering. All these factors and probably more has made her travel more W. Now were waiting to see if the high is going to weaken to the N of her and start sending her more NW. Then another trough is suppossed to save the day and kick her out to sea. This is my very unexperienced answer, but this is my perception on what I have learned.
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Quoting xcool:


sorry i'm models cast.
That N. track is lookin pretty impossible right now!
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Seems Danielle has gotten past the seam between the ridges over the Atlantic. This has allowed a resumption of the westerly track. It's not uncommon to see a storm slow down while it makes an abrupt shift in movement. In this case, Danielle shifted directions without missing a beat. Looked like a jail break to me. I suspect that this will portend a more westerly track than the current models are showing.
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2350. xcool


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2349. xcool
hydrus .WOW BIGG WAVE.keep an eye on
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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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