Tropical Depression Two forms from Invest 98L

By: Dr. Jeff Masters , 9:33 PM GMT on July 17, 2011

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Tropical Depression Two (TD2) formed from Invest 98L this afternoon. Hurricane Hunters flew into the suspect area and found a surface circulation north of the Bahamas, with maximum sustained winds of 35 mph. They also determined the system had become warm core—a characteristic that must be present in order to declare a tropical cyclone. Satellite imagery continues to show the system is becoming more organized with a stronger circulation. Wind shear is forecast to remain favorable for the system until Tuesday or Wednesday when higher shear will slide in from the north. Sea surface temperatures are warm enough to sustain a tropical storm.


Figure 1. Satellite imagery of Tropical Depression Two in the Atlantic, east of Florida. This graphic will update to the current satellite imagery.


Figure 2. Official 5-day forecast for Tropical Depression Two. This graphic will remain current.

Forecast for TD2

The models are coming into better agreement as TD2 has become more organized. In terms of dynamical forecast models, the HWRF and GFS both forecast TD2 to max out just above tropical storm strenth. HWRF intensifies TD2 to around 47 mph in the next 24 hours, whereas GFS is a bit slower to bring the system up to tropical storm status. Two statistical models, the DSHP (SHIPS model that includes land interaction) and the LGEM (Logistical Growth Equation Model) both intensify TD2 to a moderate tropical storm over the next 2-3 days.

There tends to be a lot of uncertainty involved with tropical cyclones that form under these circumstances, but our forecast remains in line with the National Hurricane Center and the reliable forecast models. TD2 will move slowly to the northeast in weak steering currents over the next few days before eventually becoming an extratropical storm. There is minimal chance that this system will cross over Florida into the Gulf of Mexico. Timing and path depend heavily on how intense the cyclone gets, as Jeff mentioned in his blog earlier today. A weaker storm will tend to stay south, whereas a stronger storm will grow taller in the atmosphere and winds at higher levels will influence it and steer it northeast.

None of the reliable models predict tropical cyclone development over the remainder of the Atlantic through July 23.

Angela

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Quoting SouthDadeFish:
1001mb... Goodnight everyone.


my eyes are crossing too, goodnite
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Quoting SouthDadeFish:
1001mb... Goodnight everyone.
Good night. I'll probably be up until the 5a.m update, lol.
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1001mb... Goodnight everyone.
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Post 882 jrrp
I am on my blackberry and can't really make that out on my screen. What does it show? Thanks
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Quoting cchsweatherman:


In order for the forecast to be correct, we will need to see northward motion within the next 24 hours with Tropical Storm Bret, which is showing no signs of doing so yet. If not, then this could become a different ball game as ridging will build in and the trough will be exiting.


time will only tell...
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920. JLPR2
Quoting JRRP:

yes

CMC muestra algo pasando bien la norte de las antillas....


El CMC muestra un pedazo de energía desprendiendose de la parte superior del disturbio y no el disturbio como tal, por eso lo pasa tan al norte.

Seems that I'll have a disturbance in my area just in time to ruin a long weekend. -.-
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Latest dropsonde into circulation has pressure down another millibar to 1001mb.

000
UZNT13 KNHC 180653
XXAA 68078 99271 70778 08077 99001 27415 23009 00010 27415 23009
92698 22601 19007 85439 21657 35503 88999 77999
31313 09608 80637
61616 AF308 0202A BRET OB 09
62626 EYE SPL 2713N07781W 0639 MBL WND 22509 AEV 20802 DLM WND 22
507 000849 WL150 23009 083 REL 2713N07781W 063743 =
XXBB 68078 99271 70778 08077 00001 27415 11934 22801 22888 24057
33850 21657 44849 21457
21212 00001 23009 11927 18507 22919 20010 33864 29504 44849 36003
31313 09608 80637
61616 AF308 0202A BRET OB 09
62626 EYE SPL 2713N07781W 0639 MBL WND 22509 AEV 20802 DLM WND 22
507 000849 WL150 23009 083 REL 2713N07781W 063743 =
;
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Quoting MiamiHurricanes09:
I completely agree. Do I think it's likely that it will reach category 2 status? No. Is it possible? Certainly.


I'll say I give it a shot to bomb. Not much of one, but I'd say at least a 1 in 4. It's sitting over a decent pool of water, the sheer isnt going to stop it. The real limit seems like it'd be the dry air to its NW, but it looks like it has enough of a buffer to not worry too much.

I think it's a waiting game til morning, see how he reacts to that big new CDO. False color shows what looks to be two hot towers in the e and s with the S being the more impressive. Keep an eye on those and we'll see how he likes the new steering layers.
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I refresh the page and im listening to youtube, so i hear a sound i x'ed out youtube and on this page a commercial for shaving gel for women, IM A MAN thanks wunderblog for the mixed emotions - Love Shadoclown45
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Quoting wxhatt:


your right, not short term anyway.


In order for the forecast to be correct, we will need to see northward motion within the next 24 hours with Tropical Storm Bret, which is showing no signs of doing so yet. If not, then this could become a different ball game as ridging will build in and the trough will be exiting.
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Center has moved east from last fix...
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913. JRRP
Quoting JLPR2:


That must be the same vort max that the GFS showed entering the Caribbean at exactly that time frame but more to the south.

yes

CMC muestra algo pasando bien la norte de las antillas....

and UKM
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I might as well wait up for the VDM. I would like to see what the dynamical models now think with a much lower pressure initialized.
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Quoting cchsweatherman:


Yes I do see the break between the ridges, but with a flat, very low amplitude trough well to the north and not digging into the break at all, its not gonna have much, if any influence in the short term on Tropical Storm Bret.


your right, not short term anyway.
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Looks like Melbourne will be getting a pretty nice band from Tropical Storm Bret through the early morning hours.
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Quoting TomTaylor:
I believe what the BAM suite was trying to show was that the more the system intensifies, the more it will be pulled to the NE (as Dr. Masters had mentioned). However, should Bret intensify enough to be steered by the deep layer (cat 2/3 hurricane) it would be steered more by the ridge allowing it to head west.

That may no longer be the case as these are fairly old model runs (8pm EDT), but at the time when the models were run, this is what the BAM suite was indicating...intensification would allow it to move more the NE, but if it intensified even more, then it would actually go to the west.
I completely agree. Do I think it's likely that it will reach category 2 status? No. Is it possible? Certainly.
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Quoting TomTaylor:
I believe what the BAM suite was trying to show was that the more the system intensifies, the more it will be pulled to the NE (as Dr. Masters had mentioned). However, should Bret intensify enough to be steered by the deep layer (cat 2/3 hurricane) it would be steered more by the ridge allowing it to head west.

That may no longer be the case as these are fairly old model runs (8pm EDT), but at the time when the models were run, this is what the BAM suite was indicating...intensification would allow it to move more the NE, but if it intensified even more, then it would actually go to the west.
I think we're all saying the same thing just in a different way. I'm assuming there is no way in heck this thing makes it to cat 3. But I guess there is a small chance for everything.
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Quoting cchsweatherman:
Just did some analysis and noticed that the trough that is forecast to influence Tropical Storm Bret seems to be flattening out while the SE US ridge seems to be nosing out over the Carolinas and directly north of the storm.



indeed it does, this may bode well for florida
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Quoting VAbeachhurricanes:
Bret still has plenty of work to do to become even close to a hurricane, satellite presentation still only a comma shape.


your right, never seen a sat presentation like that for strong TS
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Quoting SouthDadeFish:
True but the environment its in could be more favorable. 10-15 knots of wind shear and dry air getting pushed in from the NW. Although that pressure drop was impressive he may have leveled off for now. But knowing the tropics, I'll go to sleep now and he'll bomb into a hurricane. Goodnight everyone, I hope I didn't cause too many problems, just trying to offer my differing opinion. Everyone here teaches me a lot so I thank you all :~)


All opinions are welcome just as long as their civil. This is all a learning community pretty much.
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Quoting MiamiHurricanes09:
That is true, but in this case it depends on the perimeters present in the atmosphere. There is an upper-level ridge located over the United States that would influence the steering of Bret, should it intensify to the point that it can feel deep-layer steering.
I believe what the BAM suite was trying to show was that the more the system intensifies, the more it will be pulled to the NE (as Dr. Masters had mentioned). However, should Bret intensify enough to be steered by the deep layer (cat 2/3 hurricane) it would be steered more by the ridge allowing it to head west.

That may no longer be the case as these are fairly old model runs (8pm EDT), but at the time when the models were run, this is what the BAM suite was indicating...intensification would allow it to move more the NE, but if it intensified even more, then it would actually go to the west.
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Quoting Stormchaser2007:


Still 4-5 hours of the diurnal maximum for this to organize.
True but the environment its in could be more favorable. 10-15 knots of wind shear and dry air getting pushed in from the NW. Although that pressure drop was impressive he may have leveled off for now. But knowing the tropics, I'll go to sleep now and he'll bomb into a hurricane. Goodnight everyone, I hope I didn't cause too many problems, just trying to offer my differing opinion. Everyone here teaches me a lot so I thank you all :~)
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Quoting wxhatt:


but you'll notice that there is no banana shaped ridge over top. nosing out, maybe, but there is a definite break between the US ridge and the mid-atlantic ridge.


Yes I do see the break between the ridges, but with a flat, very low amplitude trough well to the north and not digging into the break at all, its not gonna have much, if any influence in the short term on Tropical Storm Bret.
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898. JLPR2
Quoting JRRP:
just in case you have forgotten

euro
00z
144h


That must be the same vort max that the GFS showed entering the Caribbean at exactly that time frame but more to the south.
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Quoting SouthDadeFish:
Bret starting to look ragged on IR again. Very confusing storm.
It dosn't look that ragged, Looks better than Arlene for sure, and IMHO I strongly believe that this storm has a good chance of achieving hurricane status my monday night-tuesday and im surprised at how fast this came to be like a top XD.
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Bret still has plenty of work to do to become even close to a hurricane, satellite presentation still only a comma shape.
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Gonna wait for the VDM/Sonde.

Probably another 45-50kt message.
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Quoting SouthDadeFish:
Bret starting to look ragged on IR again. Very confusing storm.


Still 4-5 hours of the diurnal maximum for this to organize.
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Quoting MiamiHurricanes09:
65mph winds found right before entering the circulation (northeastern semicircle). Although the depth of the water might have an effect on the SFMR instrument, I strongly believe that Bret is not a 45mph TS.

063130 2717N 07749W 8499 01474 //// +145 //// 097040 042 056 012 01


Agreed. I strongly believe we have a solid tropical storm on our hands that continues to steadily strengthen as it continues to drift general southward.
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I don't believe those SFMR readings. No flight level readings above 50 knots in that set. I think Bret is a 50mph TS but probably not more than that.
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I think we will see a special statement shortly with them upping the winds to 60 mph and issuing a hurricane watch
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Quoting Stormchaser2007:
56 knots
(~ 64.4 mph)


WOW.
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Quoting cchsweatherman:
Just did some analysis and noticed that the trough that is forecast to influence Tropical Storm Bret seems to be flattening out while the SE US ridge seems to be nosing out over the Carolinas and directly north of the storm.



but you'll notice that there is no banana shaped ridge over top. nosing out, maybe, but there is a definite break between the US ridge and the mid-atlantic ridge.
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64/65mph winds found right before entering the circulation (northeastern semicircle). Although the depth of the water might have an effect on the SFMR instrument, I strongly believe that Bret is not a 45mph TS.

063130 2717N 07749W 8499 01474 //// 145 //// 097040 042 056 012 01
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Bret starting to look ragged on IR again. Very confusing storm.
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SFMR

56 knots
(~ 64.4 mph)
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Quoting VAbeachhurricanes:
Time: 06:25:00Z
Coordinates: 27.5333N 77.5333W
Acft. Static Air Press: 848.4 mb (~ 25.05 inHg)
Acft. Geopotential Hgt: 1,526 meters (~ 5,007 feet)
Extrap. Sfc. Press: -
D-value: -
Flt. Lvl. Wind (30s): From 108° at 25 knots (From the ESE at ~ 28.7 mph)
Air Temp: 12.6°C* (~ 54.7°F*)
Dew Pt: -*
Peak (10s) Flt. Lvl. Wind: 34 knots (~ 39.1 mph)
SFMR Peak (10s) Sfc. Wind: 46 knots (~ 52.9 mph)
SFMR Rain Rate: 21 mm/hr (~ 0.83 in/hr)
(*) Denotes suspect data

Tons of these 50-60 mph surface readings, I wonder why they only went up to 45mph
because the forecasters are math weenies, and are conservative
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Quoting wxhatt:


Yes, that is a 'big' if, and not been forcasted yet.
I agree, I don't believe it will have sufficient time to intensify to the point that it will be influenced by the upper-level ridge. The possibility still exists though...weirder things have happened before, lol.
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882. JRRP
just in case you have forgotten

euro
00z
144h
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Quoting MiamiHurricanes09:
That is true, but in this case it depends on the perimeters present in the atmosphere. There is an upper-level ridge located over the United States that would influence the steering of Bret, should it intensify to the point that it can feel deep-layer steering.


Yes, that is a 'big' if, and not been forcasted yet.
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880. Skyepony (Mod)
Play with the steering currents. The deeper this gets the higher in the atmosphere it's affected by steering currents. Currently the higher you go the stronger & wider the currents flowing clockwise around the big heat wave get. Pretty pronounced weakness there too. I can see why we are still getting a somewhat squashed spider look to the model runs.
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Quoting wxhatt:
As quoted from the blog update:

"Timing and path depend heavily on how intense the cyclone gets, as Jeff mentioned in his blog earlier today. A weaker storm will tend to stay south, whereas a stronger storm will grow taller in the atmosphere and winds at higher levels will influence it and steer it northeast."
Up to a point, the more it intensifies, the more it will be steered to the NE. However, if it reached an even higher intensity, it would be steered by deep layer steering, which would allow it to be steered west by the deep layer ridge to the NW.

This is can be seen by the BAM models.



BAM Mid level indicates a NE track, while the BAM Deep layer takes it west.

So, maybe if Bret reached cat 2/3 strength, it would begin to take a westward track, but for now, as long as it intensifies, it will be pulled stronger to the NE. Hope this makes sense.
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I looked at the steering currents for every layer and they all show the same weakness between the two ridges.
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"Looks to have 'wobbled' towards the east in the last few frames. Just an observation, not saying that this is true movement."

Yes, this is part of the loop; it will then begin to move in more of a northerly component.
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Just did some analysis and noticed that the trough that is forecast to influence Tropical Storm Bret seems to be flattening out while the SE US ridge seems to be nosing out over the Carolinas and directly north of the storm.

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Thank you Jesus for the NHC. Even they underestimated this one. 19N81W just radioed me and said it's a bumpy ride tonight. :)
Member Since: May 26, 2011 Posts: 0 Comments: 1193

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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.