Tropical Storm Leslie Update #2

While some outlets are beginning to talk about Leslie .. majority of the ones that we have come across have just basically parroted what the National Hurricane is saying and really put no analysis into there discussion. We ARE NOT that way and we will never be that way. We like to let our readers know what is happening and what is going on with the tropical systems and whether or not this will effect the USA or not. At this point and time we would say that the potential is on the table for this to effect the USA but ..if we had to place a percentage it would only be at around 40% . Now that can go up and by the time we are done here you will not only see but you will understand WHY. 

So the very first thing that we are going to do is we are going to take a look at the atmosphere around Leslie and also a recent microwave image... 

Lets start with the recent microwave image and this is KEY and is very important.

Here you can actually see that the mid level system is decoupling away from the lower level center. Basically what this means is that the system will end up being slower to intensify. In addition to this when you look at 200 MB level vorticity and , 500 and 700 levels you also see that this is not a vertically stacked system..

Now why is this important? This is important because it makes the system weaker. When a system is weaker ..it becomes subjected to the steering currents that are in place.

What do we see to the North of Leslie? Well further north is Hurricane Kirk which is moving NE around the periphery of the subtropical high but we are talking immediately north of Leslie..we see the currents are showing a subtropical ridge that extends back to just to the East of Remnant low pressure Isaac. What this tells us as a forecaster is that when you see subtropical ridging to the north and you have a weaker, not vertically stacked tropical system it more or less has to follow those currents which are from East to West which means that Leslie should continue to move off towards the West towards the Lesser Antille Islands. Matter of fact guidance has this much closer to the Islands then the National Hurricane center does and we will look at that in a few moments.

Some other factors that Leslie is encountering this early morning hours is the dry air that is around the system. You can see this dry air in the image below and you can see the dry air also in the water vapor image..

Matter of fact the water vapor image shows there is more dry air then what the CIMSS image above is showing from 00z. Remember in a developing cyclone dry air penetrating into a cyclones center of circulation helps the system to develop slower..

The next two images are wind shear and shear tendency images which tell you whether the shear is rising or decreasing and while currently there is not much shear effecting the system ..there is all around the system and you can also see on the tendency map that there is a rising area of shear to the systems NW..

At the present time convergence and divergence is decent across the system. So with the current atmosphere or environment out of the way ..lets look at the guidance and the first thing we want to point out is the difference between the GFS at 66 hrs and the NHC track that was issued earlier in the evening.

Do you notice a difference between the NHC track on the right and the GFS on the left? GFS is much closer to the Lesser Antille Islands then NHC. Matter of fact NHC has been showing this having NW movement since they started issuing there tracks and yet the cyclone has been moving Westwards..

Now there most recent 5 AM update has this as the center coordinates (and lets just say we need recon out there cause once you see the visible you are going to be scratching your heard a bit)

5:00 AM AST Fri Aug 31
Location: 15.2°N 47.8°W
Moving: WNW at 16 mph
Min pressure: 999 mb
Max sustained: 65 mph

That would put the center right around just north of where the brightest bands of convection are which is the coldest cloud tops. It also does not appear to have good outflow in all quadrants .. Never the less the track they issued earlier was too far north and the GFS is not the only model showing that .. 

So lets look at the guidance ... and what the guidance is suggesting is that Leslie will find a break in the ridging and start to move towards the north but then will greatly slow down its movement. Then ridging builds back in from the east towards the west and starts to put Leslie on a NNW heading and in some cases (GFS) NW heading towards Southern New England..

These models are fairly well in remarkable agreement with the slow movement of the storm and the resulting ending place which is near Southern New England to Nova scotia. 

The moral of the story is that Tropical Storm Leslie is NOT in a completely hostile environment but not in the most friendly environment. We think slow steady strengthening is likely to continue and we feel pretty much that a west movement should continue with ridging in place. It remains to be seen if the ridging will just vanish day 3 as NHC seems to suggest..

That is day 3 and you can still clearly see ridging in place.. If the ridging "vanishes" what would cause the storm to extremely slow down? Usually things slow down if they have ridging building back over top of them and that can slow them down or even stall them..but regardless what both models here are suggesting is a very STRONG hurricane that has the potential at least to come up along the coast and perhaps end up effecting Southern New England or Nova Scotia...

We will update this in about another 24 hrs!