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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1449. jonelu
Quoting breald:


Why?

Because its showing a New England hit...so people are going to go nuts..even though it too far out to know for sure.
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Quoting breald:


Why?



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Quoting CaribBoy:
Per 18Z GFS, D, E and F may not be fishes

hey, do you want to paste the link on here, hey, how's everything in St.Maartin or St.Martin?
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1445. Skyepony (Mod)
Quoting westernmob:
I see where a NASA DC-8 part of the Hurricane Hunters is going to the GOM tomorrow for a research mission. Wonder if they have an area of concern?


That was scheduled for today..

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.

near wrapping up I suppose.. I haven't found the data but AF301 went out chucked a dropsonde at that area of interest (1011mb) from 400mb then went to 1300' & flew through it once with the SFMR on found up to 38kt surface winds.. a little less at flight level. Good change of wind direction.. E to NE, NNE to NW noted.
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1444. RJT185
Quoting KanKunKid:


NYC could use a good pressure washing.


Understatement. Still, pretty compelling runs on the GFS model.
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1443. jonelu
Quoting westernmob:
I am trying to remember the last Major Hurricane to threaten the Metro NYC area. Gloria in the 1980's comes to mind.


Hurricane Bell 1976
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Quoting westernmob:
I am trying to remember the last Major Hurricane to threaten the Metro NYC area. Gloria in the 1980's comes to mind.
hurricane Bob came close, but Floyd made a direct hit, but was only a tropical storm at the time
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Quoting jonelu:
with the latest GFS run...this blog will go looney for sure.
yeah, possibly 3-4 tropical systems at once
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1437. breald
Quoting jonelu:
with the latest GFS run...this blog will go looney for sure.


Why?
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1436. xcool
anyway next RUN BY 00Z GFS
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1435. jonelu
with the latest GFS run...this blog will go looney for sure.
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I am trying to remember the last Major Hurricane to threaten the Metro NYC area. Gloria in the 1980's comes to mind.
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Quoting CosmicEvents:
As I understand it, the long-term forecast for Danielle, from advisory #1 and continuing now, has always called for greater uncertainty on Day 4-5+ due to the balance of the exact timing of the cyclone's speed and the where and when of it's strength. Since the first advisory, the storm at first strengthened faster than expected, then weakened more than expected. Still, with all this, it's averaged out so that the storm has been well within any NHC cone in the 3-5 day period. That's good, isn't it? Doesn't the NHC themselves say that their is a signifigant amount of the time(20-30%??) the storm will find itself outside of the cone 120 hours out? So far, with Danielle, she's been in the cone. The NHC...in the zone.
yea but the shift the cone along with the way the storm is going
Member Since: August 5, 2007 Posts: 0 Comments: 714
1429. Skyepony (Mod)
Quoting Sting13:
I have 2 questions that are bugging me.

1) Why does the GFS take so long to update?
2) A post above says "major hurricane hitting NE" in 18z run. But the pressure is 980, and thats only cat 1, can GFS not predict pressures?


GFS is pretty well known to not predict pressures well. Not good for intensity guidance..
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I see where a NASA DC-8 part of the Hurricane Hunters is going to the GOM tomorrow for a research mission. Wonder if they have an area of concern?
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Quoting Stormchaser2007:
Wow

At 168 hours Danielle is approaching the CONUS

This is quite a run.

174



Looks like there playing follow the leader. I hope Bermuda is spared.
sheri
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Quoting Sting13:
I have 2 questions that are bugging me.

1) Why does the GFS take so long to update?
2) A post above says "major hurricane hitting NE" in 18z run. But the pressure is 980, and thats only cat 1, can GFS not predict pressures?


Pressures are lower that what the model shows on the GFS.
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Quoting KEEPEROFTHEGATE:
there all coming to jasons house for a one on one interview utube this
h


Lmfao wow...... best laugh I've had all day
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eyewall forming???
Member Since: August 1, 2006 Posts: 28 Comments: 3716
Per 18Z GFS, D, E and F may not be fishes
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1421. Halyn
Quoting WaterWitch11:
oh my lord - it's 104 degrees here - 90 miles north of san francisco!
I used to live in Santa Rosa .. and I never remember the temperatures getting that high! Our weather then (1998) was almost perfect .. :) Where I live now is an entirely different story :( (St. Louis area)
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Uh-Oh:

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1418. HarryMc
Quoting KEEPEROFTHEGATE:
wow i best disengaged that tractor beam or i will be tracking them right to toronto

Yep. Please either disengage the tractor beam or arm the photon torpedoes. I'm staying mum until a couple more models come out.
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1417. Sting13
I have 2 questions that are bugging me.

1) Why does the GFS take so long to update?
2) A post above says "major hurricane hitting NE" in 18z run. But the pressure is 980, and thats only cat 1, can GFS not predict pressures?
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Quoting ROBTX09:
landfall appears to be natucket island

Well very close to long island also....very very close
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1415. KEEPEROFTHEGATE (Mod)
there all coming to jasons house for a one on one interview utube this
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Big area of dry air still in front of Danielle. Also notice the Gulf of Mexico and Caribbean, they're covered in moisture.

Water Vapor:

Image and video hosting by TinyPic
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1413. NJ2S
Quoting barotropic:
18z shows daneille hits eastern tip of long island as strong hurricane.


link?
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1411. xcool
NJ2S .yep
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18z shows daneille hits eastern tip of long island as strong hurricane.
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1409. NJ2S
Quoting xcool:
wait for next run ooz by gfs


good idea no need to panic lol
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1407. xcool
wait for next run ooz by gfs
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Link
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1404. KEEPEROFTHEGATE (Mod)
Quoting MiamiHurricanes09:
168 hours, Danielle, Earl, and Fiona. Danielle approaching the U.S with a banana ridge to the north this is heading W/WNW.

wow i best disengaged that tractor beam or i will be tracking them right to toronto
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Quoting Stormchaser2007:
Wow

Major Hurricane for the NE?

Wow, very impressive. Looks like Bermuda gets a double hit in that run too.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
1402. Sting13
Lol seems 18z run, danielle is stuck over bermuda for like a whole day or more. Thanks for your reply too storm :)
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Quoting jason2010xxxx:
I do not like that huge ridge of high pressure over the Northeast that will make lots of hurricane hit the east coast.



you said 200% fish storm recall??
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A new analog storm for Danielle if this holds that no one thought of

How about Felix in 1995?
Member Since: March 10, 2010 Posts: 1 Comments: 7831

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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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