ATL : TROPICAL DEPRESSION ERIKA (06L)

[Derek Ortt]

Derek, I think you should use a football (American) infraction instead of a red card. Most of us don't know what that is

to those who do not know what the red card is, lol

[Emmett_Brown]

Some observations from the cheap seats...I am not an expert.

The reason that the NHC is concerned about 94L's possibility of development, rather than assuming shear will destroy it is because the shear is hauling westward rapidly. For instance, take a look at the Wisconsin Shear tendency map. http://cimss.ssec.wisc.edu/tropic/real- ... g8sht.html

If you compare the 18Z shear map to the 15Z map, it is clear that the ULL that is causing the shear is moving westward at a good clip. The models (GFS, NOPGAPS, CMC, NAM) show this continuing. Essentially, this is a race that 94L has to lose in order to develop. If it moves westward too rapidly, the shear eats it. If the shear moves more quickly, 94L has a decent chance.

Furthermore, in determining where exactly the MLC of 94L is, the Wisconsin 850mb vorticity can help. Between the 15Z and 18Z updates, the 850mb vorticity has gotten stronger, and is more or less co-located with the big ball of convection. If a surface low were to become established, it would likely be here. http://cimss.ssec.wisc.edu/tropic/real- ... 8vor4.html

Nice post. I checked the shear tendency maps you reference, and you are right, the tendency is for the shear to move westward in tandem with the storm, so that is keeping it from being blown to smithereens for the time being. Although the GFS has few friends right now, it does show a nice anticyclone forming over 94L in by 8pm EDT tomorrow evening. If this verifies, could allow the storm to start organizing later tomorrow:

[cycloneye]

Derek,Dr Jeff Masters is in your camp. He made an update this afternoon.

Invest 94L getting sheared
Tropical wave (94L) about 450 miles east of the central Lesser Antilles Islands, continues to be a threat to develop into a tropical depression. However, recent satellite wind shear analyses by NOAA/Colorado State University show that wind shear has increased throughout the day over 94L, and is now near 20 knots, which is marginal for development. Satellite shear analyses from the University of Wisconsin show about 10 - 20 knots of shear, and it is apparent from satellite imagery that shear is causing some disruption to the west side of 94L. Visible satellite imagery show that 94L does not have a surface circulation center, and the storm has not significantly increased in organization this afternoon.

The forecast for 94L
Wind shear as diagnosed by the SHIPS model currently shows a low amount of shear, 5 - 10 knots, and this is not correct, so this model's forecast of low shear over 94L for the next five days cannot be trusted. The latest set of 12Z model runs are more restrained in developing 94L, and are depicting higher levels of shear will be affecting 94L over the next three days. SSTs will be warm, in the 28 - 29°C range, and dry air should have only a minor inhibiting effect, but the high shear may delay 94L from developing into a tropical depression for several days. The HWRF makes 94L into a strong tropical storm 5 days from now, but the GFDL and GFS models do not develop 94L at all. The ECMWF and NOGAPS models predict that development of 94L will not occur until five or so days from now, in a region between the Bahama Islands and Bermuda. NHC continues to give 94L a high (greater than 50% chance) of developing into a tropical depression by Wednesday. This probability may need to get scaled back to moderate (30 - 50% chance) if the high shear continues into tomorrow.

[clfenwi]

not really sure why they are saying marginally favorable. There is not much favorable about the current environment

The thing that got me was saying conditions are marginally favorable and then go on to state there is a high chance of tropical storm formation. Granted that is a 'glass is half full/half empty' kind of statement that they are using to mean 'half full', as it were. However, given the trend of the season and the boogy-men that have been lurking (Unforecast ULL of Doom! Unanalyzed mid-level shear!, etc.), I would equate marginally favorable conditions with <50% chance of development.

(Granted it is easy to nitpick and over-analyze the TWOs, but this one really didn't go well with me).

[Aric Dunn]

relocation of center is likely over the next 6 hours. The convection that was on the west side that has been somewhat sustaining a small vort today has died and should no longer inhibit the sytem. So we should see a center develop farther east and north over the next few hours and over night which will put in under less shear being farther east. Up around 16N to 17N and around 55W through out the night.

[tailgater]

I'm still looking and can't find an LLC to track I've been doing this for a looong time and all I see is an eloongated low(if that) the last few visible pics make it look like it is less organized to me.

[Stormcenter]

He must read this board.

Derek,Dr Jeff Masters is in your camp. He made an update this afternoon.

Invest 94L getting sheared
Tropical wave (94L) about 450 miles east of the central Lesser Antilles Islands, continues to be a threat to develop into a tropical depression. However, recent satellite wind shear analyses by NOAA/Colorado State University show that wind shear has increased throughout the day over 94L, and is now near 20 knots, which is marginal for development. Satellite shear analyses from the University of Wisconsin show about 10 - 20 knots of shear, and it is apparent from satellite imagery that shear is causing some disruption to the west side of 94L. Visible satellite imagery show that 94L does not have a surface circulation center, and the storm has not significantly increased in organization this afternoon.

The forecast for 94L
Wind shear as diagnosed by the SHIPS model currently shows a low amount of shear, 5 - 10 knots, and this is not correct, so this model's forecast of low shear over 94L for the next five days cannot be trusted. The latest set of 12Z model runs are more restrained in developing 94L, and are depicting higher levels of shear will be affecting 94L over the next three days. SSTs will be warm, in the 28 - 29°C range, and dry air should have only a minor inhibiting effect, but the high shear may delay 94L from developing into a tropical depression for several days. The HWRF makes 94L into a strong tropical storm 5 days from now, but the GFDL and GFS models do not develop 94L at all. The ECMWF and NOGAPS models predict that development of 94L will not occur until five or so days from now, in a region between the Bahama Islands and Bermuda. NHC continues to give 94L a high (greater than 50% chance) of developing into a tropical depression by Wednesday. This probability may need to get scaled back to moderate (30 - 50% chance) if the high shear continues into tomorrow.

[Aric Dunn]

latest model errors... not so good.. with the BAM models doing the best by far.

http://hurricane.methaz.org/tracking/st ... _perf.html

nogaps for first 24hrs is the best i saw .. hwrf terrible.. lol

[cycloneye]

18z NAM.

[Evil Jeremy]

latest model errors... not so good.. with the BAM models doing the best by far.

I never thought I would ever read the words "BAM" and "Best" in the same sentence lol.

[Aric Dunn]

latest model errors... not so good.. with the BAM models doing the best by far.

I never thought I would ever read the words "BAM" and "Best" in the same sentence lol.

lol .. yeah pretty funny..

[BigA]

18Z NAM allows development because it develops a 200mb anticyclone over 94L in the 24-36 hour range, essentially having the shear lift northward and westward faster than 94L moves in that direction. I don't know that NAM is reliable at all for shear, but 24-36 hrs is not that long a forecast, and I think someone mentioned that the 12Z GFS forms a cimilar Upper level anticyclone.

[dtaylortgo]

Where do you guys think this will be in 6 days if it does develop? Im suppose to be leaving for a cruise from florida on sunday? Will we leave in time?

[Evil Jeremy]

Where do you guys think this will be in 6 days if it does develop? Im suppose to be leaving for a cruise from florida on sunday? Will we leave in time?

I am sure you will leave, though you might have some itinerary changes.

[cycloneye]

At 72 hours 18z GFS is just northnortheast of Puerto Rico.

[artist]

Where do you guys think this will be in 6 days if it does develop? Im suppose to be leaving for a cruise from florida on sunday? Will we leave in time?

I personally think with the condition this is in right now it is still a little early to tell. Where are you going on your cruise?

[BigA]

Certainly an impressive blowup of convection in the past hour near where Aric hypothesizes that the center might reform. The convection doesn't look to me to be shear-induced, so I reckon if 94L is to form a center, that would be a good place to look, as it is co-located with the most intense 850 mb vorticity.

[Aric Dunn]

relocation of center is likely over the next 6 hours. The convection that was on the west side that has been somewhat sustaining a small vort today has died and should no longer inhibit the sytem. So we should see a center develop farther east and north over the next few hours and over night which will put in under less shear being farther east. Up around 16N to 17N and around 55W through out the night.

rough drawing of where center should begin to take shape tonight.. with the absence of the other vort we should see increased inflow from the sw into this area circled, and there is some evidence there with the first signs of some stronger curved bands developing in and around the area circled. if you run the loop you can see the new convection building wnw following the area circled. http://www.ssd.noaa.gov/goes/flt/t2/loop-rgb.html

[BigA]

relocation of center is likely over the next 6 hours. The convection that was on the west side that has been somewhat sustaining a small vort today has died and should no longer inhibit the sytem. So we should see a center develop farther east and north over the next few hours and over night which will put in under less shear being farther east. Up around 16N to 17N and around 55W through out the night.

rough drawing of where center should begin to take shape tonight.. with the absence of the other vort we should see increased inflow from the sw into this area circled, and there is some evidence there with the first signs of some stronger curved bands developing in and around the area circled.

That certainly is where the convective action is. Do you think that this center formation/reformation to the northeast will help 94L avoid the worst of the shear. I'd imagine given that the shear is moving westward it could.

[Aric Dunn]

well the farther east is.. the less the shear is and through out the day the convection to east has been under 5 to 10 kts of shear as it is right under the upper high .. so we will see what happens but the shear axis has been shifting west with the system somewhat.

only time will tell