Coordinates: 23.5N 62W
----- Current Analysis -----
Date : 03 SEP 2012 Time : 061500 UTC
Lat : 23:47:30 N Lon : 61:53:55 W
CI# /Pressure/ Vmax
3.2 / 997.0mb/ 49.0kt
Final T# Adj T# Raw T#
3.0 2.9 2.9
Center Temp : -63.4C Cloud Region Temp : -60.3C
Scene Type : UNIFORM CDO CLOUD REGION
Positioning Method : FORECAST INTERPOLATION
Ocean Basin : ATLANTIC
Dvorak CI > MSLP Conversion Used : ATLANTIC
Tno/CI Rules : Constraint Limits : NO LIMIT
Weakening Flag : ON
Rapid Dissipation Flag : OFF
This would show very little north movement with slightly more of a westerly component. Movement essentially WNW . You can also see that there really has been no strengthening but rather the weakening flag is on..which means it is in a stage where it is weakening.
From here we are going to go to some images including the wide water vapor view and closer water vapor as well as the visible satellite.
These images already are beginning to show the future of Leslie with the sheer size of the system. The coldest cloud tops are south and south west of the center as the center lies on the Northwest side of the convection via ADT.
Now why is Leslie not really gaining any strength? First of all..the larger a cyclone is the longer it will take to vertically align the mid level center with the lower level center or become vertically stacked. This has been the case from the get go with leslie and at first it was due to the fast speed, then the decoupling and it still remains not vertically stacked as you can again see by looking at the 200,500, 700 mb level vorticities..
Now another reason that we have not seen her strengthen any is because of the atmosphere. So many weather outlets when forecasting tropical systems fail to look at the surrounding environment and that can lead to many false assumptions and makes one more prone to error...
We listed two of these things in our previous outlooks:
A. Dry air being entrained into the center. Looking at water vapor wide view and close in view you can still see we are dealing with dry air but it is not quite as bad as just 24 hours ago.
B. The second thing we mentioned was wind shear. While shear is beneficial to the Severe thunderstorms it is detrimental to Tropical Development..
Now we do see the eastern side of the system still under some heavy shear but you can see by looking at the tendency image (shear) it is relaxing somewhat in the direction it is moving so it should be going into a slightly better atmosphere.
Currently movement is off to the west north west and this fits well with the current steering flow:
Convergence and divergence continue to not be an issue with this system as it is in decent convergence and divergence .
Now here is where things become a little interesting. All guidance is in agreement on this system slowing down and perhaps even stalling and showing significant intensification and then moving towards the North or North North west depending on the guidance looked at and even west (after moving North)..
So lets look at the guidance tonight and see what has happened. First would be the GFS and the GFS would appear to be the right side outlier tonight...
This is at 144 hours above and ironically it is in the same position essentially as the 00z NOGAPS. Now that raises a flag on the GFS..because the rest of the guidance is further west..yet the GFS is in line with the NOGAPS which is not a trustworthy model despite it being a global model.
Interestingly enough you can see that the GGEM or the CMC is posing a threat towards the SNE area into Nova Scotia region. Now if it was just the GGEM i would be left scratching my head and not thinking to much about the GFS being where it is ..However..
Now we have the ECM's little brother the UKMET also shifting well to the west from prior runs. Matter of fact UK is kind of interesting as from 120 to 144 it is almost as if its moving due west from the east. But wait what about the ECM?
As you can tell the ECM is showing a extremely large system and also close enough to the Southern New England area to Nova Scotia that we can not say that this will not have an effect on the east coast.
Three things when looking at guidance tonight:
1. We are going to be dealing with a Large system -perhaps the first major of the year.
2. With models (all but GFS ) trending west this has to be continued to be watched.
3. The west track is starting to happen more because the ridge to the west is going to be starting to push to the east (ala why the UK comes almost from the east due west) to its spot at 144. The other thing would be the trough that is shown over the lakes with the closed low (when looking at the ECM) you can see this feature clearly. This trough "could" end up pulling Leslie further west and it would NOT take that much further of a west relocation that then we would be talking problems for SNE...
As is now the most likely target zone will be Nova scotia as we would put that at a 60 % landfall but Southern New England can ill afford to stop paying attention.. We would place a SNE landfall at about 40 % right now.
In the mean time look for slow movement with direction being west northwest to NW and a system that should maintain for now its status as a tropical storm.
Next up date 24 hours from now (if not sooner) and will include a tracking map with a cone of uncertainty..
Happy Labor Day to those of you who celebrate the holiday from the staff here at Down To Earth Forecasting!
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