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 StormW:
Back for a short.


An epic model shift StormW, it all puts Bermuda at a much higher risk.
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For future reference...

Bermuda Maritime Operations Centre

Link
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Quoting Bordonaro:

Danielle might pull another round of RI as she pulls herself together again.

Maybe the pocket of shear has finally subsided and she has adequately moistened her dry environment.


She may be ready for a comeback but she didn't undergo RI last night lol, very very far from it. She experienced a moderate intensification burst into a hurricane and then quickly leveled off, only to crash overnight and now probably trying to come back up again gradually.
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Storm looking at the steering on cimss looks like the high building in more west. What your thought on that?
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earl will be threat to fl. down the road.....and another disturbance is close to coming off african coast..
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Levi32/StormW,

Any insight on the weakness in the high to its north and its current strength, many on here saying that its reconsolidating agian, or elongating itself west to east, erasing the weakness? If this happens, what influence will it have on Danielle?
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Quoting DestinJeff:


12Z XTRP, for reference, is over Northern Cuba.

Given the latest TWD motion of the vaugue "west", I wouldn't think the XTRP moves much ... perhaps to Key West (reference), if at all.


Well I'm just going by the movement I see on satellite which is more northerly than the 12z xtrap.
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Quoting Levi32:


Indeed, they are the gray lines on this map:

I think some of the models are seeing the ridge take over for a short while, turning Danielle perhaps back NW for a while and gain some more longitude before being fully recurved. This puts Bermuda squarely in the danger zone, which they really have been all along but the models weren't showing it.




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Interesting stuff, looks like there could be some good surf up here in NE. Could anyone provide me with a resource so I can better understand how these computer models are being created? Thank you...
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Quoting jason2010xxxx:
lets hope not its better not hit the northeast.



I thought you said it was a fish storm and it was not going to affect any one in the US at all ... if I recall you even used 100% as your probabilities

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Quoting Levi32:
Say hi to Danielle's brand new CDO.



yeap looks like low level shear is relaxing
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Link

Looks like the High is building to the west its over parts of the gulf....
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Quoting ShenValleyFlyFish:
I'm in the "we need a new numbering system camp". I think we are in basic agreement.


It should be possible to fix the SSHS, as was done to the Fujita Scale a few years ago:

Enhanced Fujita Scale


The new scale takes into account quality of construction and standardizes different kinds of structures. The wind speeds on the original scale were deemed by meteorologists and engineers as being too high and engineering studies indicated that slower winds than initially estimated cause the respective degrees of damage. The new scale lists an EF5 as a tornado with winds at or above 200 mph (324 km/h), found to be sufficient to cause the damage previously ascribed to the F5 range of wind speeds. None of the tornadoes recorded on or before January 31, 2007 will be re-categorized.


The good thing about the F/EF scales is that the number is assessed following the tornado, not before hand as the SSHS is. And they didn't have to adjust the public's perception of what a bad tornado is. EF0-EF1 are still pretty weak/non-destructive tornadoes. EF2 and above are considered severe (like a cat 3 hurricane), just as F2 and above were in the old system.

Bottom line is that Ike should have been a major. If the NHC had taken into account damage potential, not just wind speed (which may have been low), then things would have unfolded differently.
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Sah eht yks nellaf tey?
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Quoting Levi32:
Say hi to Danielle's brand new CDO.




Danielle might pull another round of RI as she pulls herself together again.

Maybe the pocket of shear has finally subsided and she has adequately moistened her dry environment.
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In fact Hurricanes101, those of us who go by pattern and steering are the biggest wishcasters of all.. Especially when we don't agree with the models.
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Say hi to Danielle's brand new CDO.



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AL, 96, 2010082418, , BEST, 0, 130N, 253W, 30, 1008, LO, 34, NEQ, 0, 0, 0, 0, 1011, 125, 40, 0, 0, L, 0, , 0, 0, INVEST, M,

Up 5mph.
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Quoting Hurricanes101:
615. Levi32 6:15 PM GMT on August 24, 2010

and yet those of us who felt Bermuda was in the danger zone, were considered wishcasters or westcasters


Welcome to my world...
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Quoting Levi32:


Indeed, they are the gray lines on this map:

I think some of the models are seeing the ridge take over for a short while, turning Danielle perhaps back NW for a while and gain some more longitude before being fully recurved. This puts Bermuda squarely in the danger zone, which they really have been all along but the models weren't showing it.




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A few sure do :)

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Quoting Levi32:


Well the xtrap will shift north at 18z.


yes it should
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627. Skyepony (Mod)
000
NOUS42 KNHC 241300
WEATHER RECONNAISSANCE FLIGHTS
CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.
0900 AM EDT TUE 24 AUGUST 2010
SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)
VALID 25/1100Z TO 26/1100Z AUGUST 2010
TCPOD NUMBER.....10-085

I. ATLANTIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. SUCCEEDING DAY OUTLOOK.....NEGATIVE.
3. REMARKS: THE NASA DC-8 WILL FLY AN 8-HR RESEARCH
MISSION IN THE GULF OF MEXICO TODAY AT 38,000 FT.
TAKEOFF TIME IS 24/1400Z.


II. PACIFIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. OUTLOOK FOR SUCCEEDING DAY.....NEGATIVE.
JWP

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Quoting will45:


theres just too much gap between xtrap and the models somethings gotta shift it looks like


Well the xtrap will shift north at 18z, but yes, the models have been too far north too fast thus far.
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615. Levi32 6:15 PM GMT on August 24, 2010

and yet those of us who felt Bermuda was in the danger zone, were considered wishcasters or westcasters
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A classic Scooby-Doo "Ruh-oh" moment for Bermuda....
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Quoting Levi32:


Indeed, they are the gray lines on this map:

I think some of the models are seeing the ridge take over for a short while, turning Danielle perhaps back NW for a while and gain some more longitude before being fully recurved. This puts Bermuda squarely in the danger zone, which they really have been all along but the models weren't showing it.



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theres just too much gap between xtrap and the models somethings gotta shift it looks like
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What would people suggest instead of the SSWS, though?
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620. CJ5
Quoting DestinJeff:
Weakness to north closing off?



Wow, that is a huge change since I checked around 10am. Concerning.
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Last six hour Danielle is moving WNW,

I though still move west till tomorrow but satellite confirm movement WNW.
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Quoting angiest:


But people were just seeing the cat 2 thing, and those aren't very dangerous, now are they?
I'm in the "we need a new numbering system camp". I think we are in basic agreement.
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Again everyone.. stranger things have happened. I'm only giving it a less then 10% chance of it actually reaching the Northeastern US.
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Quoting Hurricanes101:


most of the GFS ensembles are now to the west of Bermuda too


Indeed, they are the gray lines on this map:

I think some of the models are seeing the ridge take over for a short while, turning Danielle perhaps back NW for a while and gain some more longitude before being fully recurved. This puts Bermuda squarely in the danger zone, which they really have been all along but the models weren't showing it.



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Quoting ShenValleyFlyFish:
569. angiest 12:54 PM EST on August 24, 2010

Excellent points. However NHC was attempting nobly to convey the surge dangers and folks just weren't getting it.


But people were just seeing the cat 2 thing, and those aren't very dangerous, now are they?
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Quoting Levi32:
12z GFDL shows a Cat 3 bringing tropical storm-force winds to Bermuda, passing east of the island, but imagine if it was just a nudge farther west....which is entirely possible. It bares close watching.



most of the GFS ensembles are now to the west of Bermuda too
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Quoting DestinJeff:
Looks to be due South of 2nd TFP and bending w/wsw

Link

I really don't see what you're talking about. It looks right on track to me....
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Quoting DestinJeff:


Yeah. Very interested in the early cycle 18z to see how the angle looks between XTRP and the nearest model.
should still be pretty large. will the next trough dig as deep as it supposed to? looks like the models are starting to hedge on that question.
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AOI

AOI

AOI

AOI

AOI

TS BUSTED FORECAST ALIBI
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12z GFDL shows a Cat 3 bringing tropical storm-force winds to Bermuda, passing east of the island, but imagine if it was just a nudge farther west....which is entirely possible. It bares close watching.

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The NHC is now on the right side of the model consensus, this is NOT good for Bermuda at all!
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I noticed that, However that graphic just means that if a tropical storm were to form in Lake Erie or Lake Ontario then it has a 95% chance of hitting the US. :-) Not specifically these storms.

Quoting drj10526:
In Dr. Masters probability graphic, did anyone notice the 95% chance that one of these2 storms will hit the great lakes?
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569. angiest 12:54 PM EST on August 24, 2010

Excellent points. However NHC was attempting nobly to convey the surge dangers and folks just weren't getting it.
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Quoting DestinJeff:
Looks to be due South of 2nd TFP and bending w/wsw

Link


What are you looking at? O_O
I see a WNW motion which is on track to hit its 2nd forecast point.
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Quoting reedzone:
12Z GFDL has shifted westward quite a bit as well... EURO is next! Also the GFDL now has 96L westward.


Wow the GFDL is very far south with 96L too

has it at 20N and 54W in 5 days
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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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