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 Alockwr21:
Earl looks to have a lot more potential of effecting the US than Danielle does
too far out to tell yet. remember danielle was forecast to miss bermuda well to the east. thats not panning out.we have no skill in such long range forecasts.
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3296. 7544
looks like fla better keep 2 eyes on earl as the high builds in by the time he gets to the end of that cone
Member Since: May 6, 2007 Posts: 0 Comments: 6736
Uh guys, I'm not loving those tracks for Earl...I want fish! It is amazing to watch this monsters develop and they are almost beautiful in their swirling power but I like them to stay in the water.
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THE DEPRESSION WILL LIKELY
BECOME A TROPICAL STORM LATER TODAY AND THERE IS UNUSUALLY WARM
WATER OVER THE TROPICAL ATLANTIC...AND THE SHEAR IS FORECAST TO
REMAIN LOW FOR THE NEXT 2 TO 3 DAYS.


This is no good....I guess the ATL is really warm eventhough Danielle already stirred up those waters.
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3292. wxhatt
Now, it's not to say that it's a sure bet that any CV storm doesn't break through a trough. But I think unless there is a big pattern change the 'majority' of Cape Verde storms should stay out to sea.

We need to be more aware of in close development, especially because the MJO upward motion pulse is forcasted to make its way back this way for Sept.
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Storm has a lot to get together for his blog this AM....I can see the smoke rising from here!
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Quoting Alockwr21:
Earl looks to have a lot more potential of effecting the US than Danielle does


It looks like it may pull off an Isabel.
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3286. angiest
Danielle and TD 7:

danielle and td7
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Earl looks to have a lot more potential of effecting the US than Danielle does
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3282. Melagoo
If EARL hits the USA ... EARL CAMPBELL (Hurricane) vs JACK LAMBERT (USA)
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Quoting rwdobson:


In other words, keep watching TWC. Please.

The troughs coming through are plenty strong. Check out the low temperatures in the middle of the CONUS tonight...


Yes I can't wait, here in central Illinois it's been more like Flordia of the past month and a half. Lows tonight are to bottom out in the mid 50's!! woooooo!
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I'm not liking this track.
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Quoting tropicfreak:


Yup. We may have 3 storms in the atlantic at the same time soon.



looks like the train has left the station....
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Quoting katrinakat5:
TWC just said all interests along the easy coast should keep a very close eye on danielle.they said that they can't rule out a direct strike on the east coast ealy next week..this is unusual for TWC to say this..


Perhaps not. They've lost a lot of talent in recent years so they are now generalizing potential impacts.
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Quoting hoenn:
Danielle looking good but isn't following the models at all, she is going west at a fast paste, refuses to do her turn. She is alot like Hurricane Ike, she might never make her turn. She will become a major hurricane I think and maybe even surpass Hurricane Emily.

Earl is amazing, and will also go west. I see him hitting Miss Or LA.

I see neither as fish but strong land hitting cat 5

this is a very strong hurricane season



Are you kidding me? Go take your meds-
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Quoting katrinakat5:
TWC just said all interests along the easy coast should keep a very close eye on danielle.they said that they can't rule out a direct strike on the east coast ealy next week..this is unusual for TWC to say this..


In other words, keep watching TWC. Please.

The troughs coming through are plenty strong. Check out the low temperatures in the middle of the CONUS tonight...
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Quoting Melagoo:
... Looks like we'll have three storms in the Atlantic the next wave looks pretty good too!


Yup. We may have 3 storms in the atlantic at the same time soon.

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3272. Melagoo
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Crazy how things change...


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.
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3270. wxhatt
Quoting katrinakat5:
TWC just said all interests along the easy coast should keep a very close eye on danielle.they said that they can't rule out a direct strike on the east coast ealy next week..this is unusual for TWC to say this..


"Um, that way they keep you tuning in for updates (sponsors)" LOL
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Quoting DestinJeff:



shifted further west once again. The trend continues and now the east coast bears watching.
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3268. Melagoo
... Looks like we'll have three storms in the Atlantic the next wave looks pretty good too!
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000
WTNT31 KNHC 251440
TCPAT1
BULLETIN
HURRICANE DANIELLE ADVISORY NUMBER 16
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL062010
1100 AM AST WED AUG 25 2010

...DANIELLE CONTINUING WEST-NORTHWESTWARD WITH NO CHANGE IN
STRENGTH...


SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...19.6N 52.3W
ABOUT 710 MI...1145 KM E OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...85 MPH...140 KM/HR
PRESENT MOVEMENT...WNW OR 300 DEGREES AT 17 MPH...28 KM/HR
MINIMUM CENTRAL PRESSURE...982 MB...29.00 INCHES
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...NEW TROPICAL DEPRESSION FORMS IN THE FAR EASTERN ATLANTIC...EXPECTED TO BECOME A TROPICAL STORM LATER TODAY...
--------------------------------------------------------------------------------

11:00 AM AST Wed Aug 25
Location: 14.3°N 30.8°W
Max sustained: 35 mph
Moving: W at 17 mph
Min pressure: 1007 mb

Member Since: June 13, 2009 Posts: 2 Comments: 11670
3264. 7544
td7 might make in it the h box
Member Since: May 6, 2007 Posts: 0 Comments: 6736
Quoting Relix:
Earl still moving at 270. Expect shifts in the tracks. Northern islands seem to be in the bulls eye? =O


Yes if the trough is not as strong as forecasted, it may skirt them
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Quoting TerraNova:
Why's it being initialized at advisory #2, anybody know?


Just a slip-up, I think.

Forecast/Advisory is #1.

It'll be changed in a minute.
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3260. dmaddox
calder: navy site still has it as an invest:

Link

are you talking about another navy site?
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TD7 looking excellent in our sat images. Great call by the nhc, best looking system so far this season that the nhc has classified. Definitely looks like a TS.



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3256. Bonedog
Dmaddox at 0845 it was already listed on the NRL website. NHC just waited till 1100 as that is their normal update time. With it not being a land threat yet they felt waiting was OK.
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Quoting dmaddox:
where did you see that at Neapolitan? cant find it anywhere on NHC's website....


Which part do you mean?
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Why's it being initialized at advisory #2, anybody know?
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Quoting wayfaringstranger:


I see it now! Thanks

No prob...I didn't see it either for a while...
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3251. Relix
Earl still moving at 270. Expect shifts in the tracks. Northern islands seem to be in the bulls eye? =O
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3250. wxhatt
Even though we are getting High heights over the Northeast U.S., it's showing a weakness over the Central Atlantic.






This 500 mb Height anomoly over the N.E. is supposed to persist at least through Sept.

Unless this changes, I would be 'more concerned' with "Home Brew", rather than the Cape Verde storms.

"Big High to the north look out below..."

The Gulf is showing that now, along with the South East Coast.

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MOST OF THE NUMERICAL GUIDANCE SHOWS A
PERSISTENT TROUGH OVER THE WESTERN ATLANTIC. IF THIS PATTERN
MATERIALIZES...IT WOULD STEER THE CYCLONE TOWARD THE NORTHWEST AWAY
FROM THE LESSER ANTILLES.
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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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