Tropical Depression Six arrives

By: Dr. Jeff Masters , 5:14 PM GMT on August 22, 2010

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Tropical Storm Tropical Depression Six is here, but it will not be a threat to land for at least the next five days. Tropical Depression Six is a classic "Cape Verdes"-type storm common during the peak part of hurricane season. Cape Verdes-type storms are so named because they form from tropical waves that come off the coast of Africa and pass near the Cape Verdes Islands just west of Africa. Cape Verdes hurricanes are the largest and most dangerous types of hurricane in the Atlantic, since they spend a long time over water have and have of opportunity to reach full maturity. Tropical Depression Six has a ways to go before it becomes a hurricane, as the storm is embedded in a strong easterly flow of wind courtesy of the African Monsoon that is generating a moderately high 15 - 20 knots of wind shear. There is also a tropical disturbance to the northeast of TD 6 that is sucking away some moisture and is interfering with the storm's circulation. Sea Surface Temperatures (SSTs) are a warm 28°C, and the storm is embedded in a moist environment, so wind shear is the primary inhibiting factor for development. The strong east winds imparting the shear are keeping any heavy thunderstorms from developing on the east side of the center of circulation, which is exposed to view in satellite imagery (Figure 1.)


Figure 1. Afternoon satellite image of Tropical Depression Six.

Forecast for Tropical Depression Six
A ridge of high pressure will force Tropical Depression Six to the west-northwest for the next five days, and the system should increase its forward speed from its current 10 mph to 15 mph by Monday night. A powerful trough of low pressure over the mid-Atlantic Ocean will begin to pull Tropical Depression Six more to the northwest late this week, and the storm should pass well to the northeast of the Lesser Antilles Islands. It remains to be seen, however, it this trough will be strong enough to fully recurve Tropical Depression Six out to sea. The GFS predicts that Tropical Depression Six may pass close to Bermuda about eight days from now, and it is also possible that Tropical Depression Six could eventually hit the U.S. East Coast 9 - 15 days from now. However, we have no skill in making these sort of ultra-long range forecasts, and the long-range fate of TD 6 is uncertain.

Elsewhere in the tropics
The ECMWF and NOGAPS models are predicting formation of a tropical depression off the coast of Africa 3 - 4 days from now.

Jeff Masters

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Quoting Stormchaser2007:


Is that blue square the current center fix of Danielle RIGHT NOW or as of 11 PM? I thought its further west than that now.
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Quoting awp5141:
Link
is this the Link you were asking for ?
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2680. leo305
Quoting hunkerdown:
no, it is not "spinning like a cane" as you put it. CIMSS puts it center on the eastern periphery of the strongest convection.


I guess it's not stacked with the mid level low, because the convection is spinning.. on infared
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2679. xcool
ECMWF out sea . maybe gom storms by ECMWF
Member Since: September 26, 2009 Posts: 2 Comments: 15603
Check the visible loop now. Light is approaching. Can someone post it for discussion?
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2677. awp5141
Link
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2676. xcool
cente edge convectio
Member Since: September 26, 2009 Posts: 2 Comments: 15603
Quoting leo305:


its spinning like a cane, look at how strong the heaviest convection is spinning.. it practicly is or may be about to open an eye.. but it's collapsing on itself because of the somewhat chocked east side


I saw the convection trying to spin with the low-level circulation, and I agree its still chocked on its east side. I do think this'll be a hurricane eventually, but not by 5 AM. Give it some more time, perhaps as early as tomorrow afternoon, this could be a hurricane.

Quoting KoritheMan:


True. But keep in mind that Danielle is also moving slower than the shear vector.


Is Danielle ever going to accelerate faster to the west over the next day or two?
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Quoting leo305:


its spinning like a cane, look at how strong the heaviest convection is spinning.. it practicly is or may be about to open an eye.. but it's collapsing on itself because of the somewhat chocked east side
no, it is not "spinning like a cane" as you put it. CIMSS puts it center on the eastern periphery of the strongest convection.
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2672. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15603
Quoting JLPR2:


But if Danielle recurved wouldn't Danielle itself create a weakness for the next storm to follow?


Not necessarily. In some cases a mature hurricane's upper-level outflow can pump additional heat into the ridge, thereby strengthening it.

But you're correct: an alternate scenario would be for Danielle to leave behind a weakness in the subtropical ridge.

But the synoptic scale pattern over North America does not favor such a ridiculous and unrealistically deep trough, as depicted by the GFS. Enough to recurve Danielle? Probably. But to recurve the other area? Doubtful.
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2670. leo305
Quoting NCHurricane2009:


Dude, I agree that it looks nicer and for the first time its developing outflow on its east side, but this doesn't still look like a 'cane. This'll probably be 60 to 65 mph winds at 5 AM EDT advisory.


its spinning like a cane, look at how strong the heaviest convection is spinning.. it practicly is or may be about to open an eye.. but it's collapsing on itself because of the somewhat chocked east side
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Quoting nwFLstormstalker:


sure, theres easterly shear, we all should know that by now,but its moving westard with the shear its back. Outflow is improving(at least temporarily) and it surely has better symmetry than other tropical storms this season.


Yeah, its got better symmetry than Colin and Bonnie, but Alex's symmetry was the best of the season so far. If Danielle keeps bending its track to the west, the storm-relative easterly shear would be less on it, and this'll probably start to rival Alex as one of the cool-looking storms of this season.
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Quoting nwFLstormstalker:


sure, theres easterly shear, we all should know that by now,but its moving westard with the shear its back. Outflow is improving(at least temporarily) and it surely has better symmetry than other tropical storms this season.


True. But keep in mind that Danielle is also moving slower than the shear vector.
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2667. smuldy
Quoting NCHurricane2009:


Evening/early morning folks,

Since when did we have high confidence anyway with a Cape Verde storm this early out? LOL.

Using CIMSS steering layers, I have been watching the trough over the western US, which is supposed to become the trough that curves Danielle ultimately NW. It hasn't been track quiet as fast to the east as I predicted, but I am not adjusting my forecast track to the left until that trough further lags behind.
is it deepening as predicted? cannot really see the 8/22 current in that image as 8/23 is the first fully visible and a prediction given that ran 8/22
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Quoting leo305:
I say its very near hurricane strength.. if not already there.. by 5 am I see an upgrade

the west side is looking monstrous, the east side is fighting the hear, but it's looking much weaker, but not weak.


Dude, I agree that it looks nicer and for the first time its developing outflow on its east side, but this doesn't still look like a 'cane. This'll probably be 60 to 65 mph winds at 5 AM EDT advisory.
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Quoting KoritheMan:


Because outflow is still restricted (but gradually improving) to the east, implying easterly shear?


sure, theres easterly shear, we all should know that by now,but its moving westard with the shear its back. Outflow is improving(at least temporarily) and it surely has better symmetry than other tropical storms this season.
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2664. xcool



144HR .WEAKER CLOSE
Member Since: September 26, 2009 Posts: 2 Comments: 15603
2663. xcool
MOVE WNW OFF FORECAST POINTS
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2662. JLPR2
Quoting KoritheMan:


The weakness in the ridge isn't going to be that large, so as to be able to recurve two consecutive systems, especially one as far south as the western Africa AOI.


But if Danielle recurved wouldn't Danielle itself create a weakness for the next storm to follow?
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Quoting smuldy:
yes i think it is very possible; in fact gun to my head i think the track is off a tad east and center will pass east but very near bermuda; I'm just saying im not sold yet, thaty would be the center of my cone at 25% probability but at this point my cone would extend from cuba to about 50n 40w, the environmental conditions on this one could allow for almost anything to happen because of the strange setup the models' forecasts given the season; again jmo
That's about the size of cone I would have also. 240 hrs out. Still up in the air.
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2660. leo305
I say its very near hurricane strength.. if not already there.. by 5 am I see an upgrade

the west side is looking monstrous, the east side is fighting the hear, but it's looking much weaker, but not weak.
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2659. xcool


Member Since: September 26, 2009 Posts: 2 Comments: 15603
Quoting KoritheMan:


Yeah, it's best to watch it, since the synoptic scale pattern is still uncertain. More so than usual. Which will tend to have negative repercussions on the forecast track.


Evening/early morning folks,

Since when did we have high confidence anyway with a Cape Verde storm this early out? LOL.

Using CIMSS steering layers, I have been watching the trough over the western US, which is supposed to become the trough that curves Danielle ultimately NW. It hasn't been track quiet as fast to the east as I predicted, but I am not adjusting my forecast track to the left until that trough further lags behind.
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2657. smuldy
Quoting KoritheMan:


Yeah, it's best to watch it, since the synoptic scale pattern is still uncertain. More so than usual. Which will tend to have negative repercussions on the forecast track.
completely agreed and all i was trying to say in my earlier earlier forecastish post; didnt disagree on colin when i was here and wont disagree much in the future (i dont expect to anyway) just this is a really really really weird pattern of environmentals that the models are calling for given that it is 8/23 not 10/23
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Quoting hunkerdown:
bingo, see the loop I posted just above yours.


The weakness in the ridge isn't going to be that large, so as to be able to recurve two consecutive systems, especially one as far south as the western Africa AOI.
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2655. xcool


120hrs .
Member Since: September 26, 2009 Posts: 2 Comments: 15603
2654. smuldy
Quoting swflurker:
But if you look at cool's ECM, do you think a north track is possible with the double H's at 72 hrs?
yes i think it is very possible; in fact gun to my head i think the track is off a tad east and center will pass east but very near bermuda; I'm just saying im not sold yet, that would be the center of my cone at 25% probability but at this point my cone would extend from cuba to about 50n 40w, the environmental conditions on this one could allow for almost anything to happen because of the strange setup of environmentals in the models' forecasts given the season; again jmo
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Quoting BreadandCircuses:
that is not the COC
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Quoting smuldy:
agreed would not say that; i dont buy the tracks as yet based on other environmental conditions forecasted to occur, if the center is a little off north south east west that wont change my mind; i will change my mind IF this nor'easter that is supposed to kill the high pressure ridging is as strong an august storm as the models say it is; jmo


Yeah, it's best to watch it, since the synoptic scale pattern is still uncertain. More so than usual. Which will tend to have negative repercussions on the forecast track.
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Wow, this storm has me confused on several levels. Can't wait to see the visual once the light permits...should be quite informative

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But if you look at cool's ECM, do you think a north track is possible with the double H's at 72 hrs?
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Quoting TampaSpin:



If this sheer graphic is accurate the COC should be on the NE corner of the deep stuff as shear is 15-20mph.



bingo, see the loop I posted just above yours.
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2647. smuldy
Quoting KoritheMan:


Ugh. So true. Many here need to hear this, and actually understand it.
agreed would not say that; i dont buy the tracks as yet based on other environmental conditions forecasted to occur, if the center is a little off north south east west that wont change my mind; i will change my mind IF this nor'easter that is supposed to kill the high pressure ridging is as strong an august storm as the models say it is; jmo
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Quoting KoritheMan:


Well, it's always frustratingly difficult to accurately pinpoint a center location in storms with structures like Danielle. IR imagery only serves to worsen the problem. I could be way off in my estimate.



If this sheer graphic is accurate the COC should be on the NE corner of the deep stuff as shear is 15-20mph.



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Quoting JLPR2:
Also, if the storm is actually under the convection and waay off its forecast points it doesn't mean its track is going to change dramatically.

Had to say that. XD

watch the CIMSS loop
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Well I'm going to call it a night. Be back sometime in the next week not sure when though... Goodnight All!
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2643. JLPR2
Quoting smuldy:
any guesses by anyone (purely speculative) as to its position per the 5am given its current movement?


Well if I'm going to take a guess I would say its closer to the center of the convection but still slightly to the east, so not dead center.
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2642. xcool



96hrs ECMWF
Member Since: September 26, 2009 Posts: 2 Comments: 15603
Quoting JLPR2:
Also, if the storm is actually under the convection and waay off its forecast points it doesn't mean its track is going to change dramatically.

Had to say that. XD


Ugh. So true. Many here need to hear this, and actually understand it.
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2640. JLPR2
Also, if the storm is actually under the convection and waay off its forecast points it doesn't mean its track is going to change dramatically.

Had to say that. XD
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Quoting JLPR2:


Yes! So many high clouds, this is why I like naked spins, easier to pinpoint. XD


Same.
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2638. xcool



wave
good model support
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2637. smuldy
any guesses by anyone (purely speculative) as to its position per the 5am given its current movement?
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2636. JLPR2
Quoting KoritheMan:


Well, it's always frustratingly difficult to accurately pinpoint a center location in storms with structures like Danielle. IR imagery only serves to worsen the problem. I could be way off in my estimate.


Yes! So many high clouds, this is why I like naked spins, easier to pinpoint. XD
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2635. xcool


72hrs ECMWF
Member Since: September 26, 2009 Posts: 2 Comments: 15603
Uninhanced, if stacked, 14.1n 37.5w
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Quoting nwFLstormstalker:
COC is in center of convection. why is their such doubt about it....
no, see post 2546
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2632. mbjjm
Position Estimate from UW - CIMSS satellite 1 hour ago Lat : 14:21:53 N Lon : 36:19:29 W

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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.