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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2349. xcool
hydrus .WOW BIGG WAVE.keep an eye on
Member Since: September 26, 2009 Posts: 2 Comments: 15648
Quoting xcool:


3 STORMS.


96L/Earl aiming at the northern Lesser Antilles on that run.
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I have the coc at 18N/49.9W, westward movement, maybe a tad wobble south of due west
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2346. xcool


3 STORMS.
Member Since: September 26, 2009 Posts: 2 Comments: 15648
Quoting xcool:


72hrs .


it has it moving wnw... not liking this run at all xcool...
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good evenin fellowes... keeperofthegate... brethren and caribbean dwellers alike. looking for some good surf to hit the islands.
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2343. hydrus
Quoting xcool:
scott39 lol.yeah.gfs 1009mb lower in gom
I tried to post this loop directly to the blog, but could only link...look at this wave over Western Africa, be sure to click the loop option....This is a monster...Link
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Quoting VAbeachhurricanes:


dude... 16th inning, and wow that 60 hour GFS NOT GOOD!

I'm watching the game and looking at the GFS at the same time. :D
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Things that make you go Hummmm. Pulling another duck and run tonight?

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2340. xcool


72hrs .
Member Since: September 26, 2009 Posts: 2 Comments: 15648
2339. xcool
she move back to west now.
Member Since: September 26, 2009 Posts: 2 Comments: 15648
Quoting Racefan24:


Could you explain what you mean. Thank you I am just a beginner here


There's a pretty good video tutorial on how to view the different model pages here. You can find all the pages referenced in that video from here.

Sorry for the glitches on the site. Will have those fixed in the next few days. Server changes...

As for the "due west" comments...don't let the convection fool you.
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Any new models out for the GOM? Still hinting at anything?
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2336. KEEPEROFTHEGATE (Mod)
06L/H/D/C1
MARK
19.01N/50.25W

Member Since: July 15, 2006 Posts: 170 Comments: 53462
2335. Seastep
To clarify, models did have it being picked up by the second trough, but that was at the weakness between the highs. Different scenario.
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Quoting ChrisDcat5Storm:
Link

OMG
WOW THAT IS SCARY
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2333. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15648
Quoting philliesrock:
It's a little farther east on the 0z GFS, but the trough is weaker. When it's all said and done I think it'll be east of the 18z GFS by about 50-100 miles.


dude... 16th inning, and wow that 60 hour GFS NOT GOOD!
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2331. hydrus
.
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2330. xcool


sorry i'm models cast.
Member Since: September 26, 2009 Posts: 2 Comments: 15648
this could be storm that does what it wants steering currents or not. Computr models keep meesing up with this one all I can say is....WATCH OUT PEEPS
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2328. KEEPEROFTHEGATE (Mod)
T.C.F.A.
xx/xx/96L
MARK
12.61N/28.18W
Member Since: July 15, 2006 Posts: 170 Comments: 53462
2327. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15648
It's a little farther east on the 0z GFS, but the trough is weaker. When it's all said and done I think it'll be east of the 18z GFS by about 50-100 miles.
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2325. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15648
Quoting scott39:
I will believe it when I see it.


Scott,

Your opinion what do you think is going on?
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2323. xcool
scott39 lol.yeah.gfs 1009mb lower in gom
Member Since: September 26, 2009 Posts: 2 Comments: 15648
Quoting hurricanehunter27:
Good night everyone! Hope to see a strong storm tommorow.(Not hoping for mass destrution or anything its just they look so beautiful on the vis sat).
Have a good night.
We'll keep an eye out for you.
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Quoting Racefan24:


Could you explain what you mean. Thank you I am just a beginner here


click on the link, and every once and a while hit the refresh button in the top right corner. It is the 500mb mean, I just use it because I find it very easy to see the highs, and lows and see how they interact without the precip forecasts in the way. Dont pay attention to strength either, it is always wrong only good for track.
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Quoting CyclonicVoyage:
Danielle, Earl and look over Africa. Times are heating and this is what we've all be waiting for, fasten your seat belt folks.


Run for your lives!
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Quoting RufusBaker:
Absolutely put that latitude and longitude lines up and u can see the eye moving due west


I just did the same thing RufusBaker and I saw the same thing. I have had a few tonight and wanted to make sure that I was just not seeing things. This storm seems to be playing games with everyone.
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2318. Relix
Pre-Fiona looks good. May just be the caribbean storm of the year!
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2317. JRRP
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2316. scott39
Quoting xcool:
scott39 .no clue ...
I will believe it when I see it.
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Good night everyone! Hope to see a strong storm tommorow.(Not hoping for mass destrution or anything its just they look so beautiful on the vis sat).
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looks west to me over last few hours any1 disagree
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Quoting VAbeachhurricanes:
watch the 0z gfs here

Link


Could you explain what you mean. Thank you I am just a beginner here
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2312. xcool
scott39 .no clue ...
Member Since: September 26, 2009 Posts: 2 Comments: 15648
Quoting VAbeachhurricanes:
Link

Due west?
Absolutely put that latitude and longitude lines up and u can see the eye moving due west
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2310. scott39
Quoting xcool:
Wheres the weakness xcool?
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Quoting VAbeachhurricanes:
Link

Due west?

Looks like it to me now!
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2308. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15648
Quoting VAbeachhurricanes:
Link

Due west?


Agreed and I am no met or not even close.
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Link

Due west?
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2305. angiest
Quoting CyclonicVoyage:
Danielle, Earl and look over Africa. Times are heating and this is what we've all be waiting for, fasten your seat belt folks.


Yep, pre-Fiona possibly emerging by hour 30.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
is it still moving west who has seen the latest loop?
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Quoting scott39:
If the ridge is weakening, why is Danielle going more W?


I agree Scott. I am not trying to wish anything or any one but I honestly have been not seeing this storm do anything yet the models have been saying it was going to do. It has been more west and south of all the models.
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Danielle, Earl and look over Africa. Times are heating and this is what we've all be waiting for, fasten your seat belt folks.
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Going to be a fun few Days :)



AOI

AOI

AOI

AOI

AOI

TS BUSTED FORECAST ALIBI
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2300. Seastep
two tone.
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2299. jonelu
looks lik the air in front of Danielle is moistening a little as she slowly strengthens. But I wonder how that pesky ULL to her north will effect her.
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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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