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!

While Isaac continues to Weaken -Attention Turns East!

Seems like there is never a dull moment when it comes to forecasting the weather and in particular forecasting the tropics. While LA and portions of the south central region continue to be battered by Tropical Storm Isaac there is another Tropical wave east of the Lesser Antilles and this is up to a 90 % chance of Development...

Now what we want to do here is show some initialization of the European Computer Model and its features that are important players at this point and time at least in the upper levels of the atmosphere.

The map is pretty self explanatory. It is the 500 mb level and you can see where 98 L is located as well as the ridging that is in place as well as a small weakness in that ridge. Majority of your guidance tonight is showing it finding that weakness...

If these tracks become realized then this would NOT pose a threat to the USA. This would stay harmlessly out at sea. However.. as Tropical Forecasting has showed models generally do not have a grasp on the scenario until a center of circulation is involved and at this point and time we still do NOT have that..
We bring the ridging up initialized above because we believe it plays an important role in the short to medium term. Lets look at the steering currents as of 6 Z..

This shows you the ridging that we were talking about off the ECM and this also shows you the weakness that we referenced. Essentially what this says is that in the near term this should continue mainly on a western track..

We have some things working against fast development and that would be the dry air that is in place around the invest. 

Still yet another thing we see is that the vorticity of this system is rather stretched out and elongated.
One other thing that we have also noticed has to do with the shear and that is that it is on the increase to the west of the system..

Things in favor of development..
1. Convergence and divergence while in reality it does look off to the west a bit ..the wave is still in a decent area of each..

2. Present wind shear and the presence of an anti cyclone over top of the system..

So as you can see there are some things that would favor development and some things that we seeing that would hinder development

Now what makes this interesting is there are only 3 models that go out to 240 hrs and that would be the GGEM,GFS and ECM.. GFS and GGEM both keep future Leslie out to sea. However the European suggests that 98 L could come towards the Cape Cod region.

While this model is all alone right now in what it is showing we would be in the wrong to quickly dismiss the model just because it is alone at the present time. 

This system should continue to move mainly west with the steering currents  in place. Next update will be in 24 hrs from now ..And we think this should get named a depression within the next 12 hrs,,, Stay tuned for more coverage and out looks via our facebook page!

Brief Isaac Update .. 24 hrs to landfall ..

We just want to post a very brief update on Tropical Storm Isaac. Alot of people around the net are wondering why does this storm have a pressure of 979 MBS and yet it is still a tropical storm? The answer really lies in the three images that are below.

This first image is the Tropical Cyclone Heat Potential fields. And ideal conditions for tropical storms to develop and intensify (if you look at the scale on the right) would be anything that is 80 or above. As you can see the waters that Isaac are travelling over do not have that much heat potential. 

 Reason #2 is in the water vapor image and this is showing that there is dry air that is being entrained into the center... Dry air is never a favorable thing for systems to develop. 

Reason # 3 is that the system is still NOT vertically stacked and the mid level center is further south ... You can see this when looking at the vorticity levels at 700 ,500 , 200

Reason # 4 is the shear size of the system and the large radius of winds that it is producing. Whenever you have a large system such as Isaac it takes longer to contract and pull the convection to the center and wrap around.. So while you may have flight level winds that support a hurricane they are not making it down to the surface...

We are completely dismissing a Category 3 probability...and we are now going with at best a Category 1 hurricane. IF the dry air can be worked out of the system and we get an eyewall to close off then it is still possible to obtain a higher category..However.. we are running out of time and running out of space... It is only about 24 hrs to landfall! 

Isaac Update ... West Track is Real!

First off we want to start this off by saying that if you have been following this blog we want to thank you. We try to put out the most accurate forecast possible based on the guidance that we have available and the synoptic weather pattern and with real time observations and images. 

We have stated from the beginning that we were not going with the eastern track or up the east coast , despite a couple model runs and despite some professional agencies stating other wise. It was quite clear and evident from our eyes and view point that the subtropical ridge was going to be to strong and the weakness was going to be to weak to have any real effect on Isaac..

In review we also mentioned that Isaac would weaken before beginning to restrengthen. People keep messaging and asking well what about intensity. Unfortunately, weather is not an exact science and the intensification process does not just depend on warm waters. You have to take the whole atmosphere surrounding the system into the equation. Could Isaac become a Cat 2 hurricane or a Major hurricane? Yes that possibility is still on the table .. 

We also stated that this would take a track to the west of Florida without making a landfall in Florida. Again, this is something that has happened and occurred , outside of the keys region. When we mention florida we mean mainland florida. 

We also mentioned that it would depend on how quickly Isaac can recover from his journey across Haiti as far as final intensity level. Isaac while dropping in pressure is still struggling from shear ...this due to the ULL that has been slower to move away from Isaac. Again that is something we mentioned last night.

ALL GUIDANCE HAS NOW SHIFTED WEST!

Virtually all the guidance has now shifted west with LA (NOLA) in its site. This west track and trend was first started by the GFS and the other models have been following that model with going more west. However, it has taken the ECM which is the better statistical model to under 48 hrs to catch on to the ridge being slower. 

So lets look at tonights guidance and then we will ge into the real time atmosphere..

As you can see the above image was the 00z Early guidance and virtually at that time every model had shifted west..West of even the western panhandle of Florida.

 The above image here is the GFS and this model has been the most consistent over its past several runs and it shows a NOLA region landfall.

 HWRF a hurricane model from 00z which you can also see has shifted towards NOLA region.

 6 Z Early track guidance and you can basically see again that they are all fairly well clustered over NOLA region!

 00 Z UKMET which was one of the models that was furthest east has now decided that it did not want to be left alone and be an outlier so it to has shifted its track west and is towards NOLA region...

The above is the European Computer model or the ECM and you can see that this model has made a substantial west ward adjustment. Only problem is that it took to 48 hours and under for the ECM  to finally join the rest of the guidance!

00z GGEM the track for the particular run is in red and you can see once again that the GGEM is sticking to the NOLA region.

The above is the 00z GFDL and this model to has the NOLA in its aim. Folks there is not a question about whether or not there is going to be a track to the west of florida and there is not a doubt that this will be taking the western track towards New Orleans. There is still a small possibility that it could be the MS/AL border. However..keep in mind that the worst side to be with a hurricane is the eastern side.

We are not going to change our track because it was issued as final and we also have New Orleans in the cone of uncertainty and with discussing it all morning and evening on our Facebook page people are aware that we were shifting the focus to New Orleans..

Now lets look at the current conditions and a latest image of Isaac..

Isaac is beginning to get his act together and with the warm waters that are in place he should have no problem becoming a hurricane. As mentioned above part of the reason why he has been struggling (and really folks that is a blessing) is because the ULL to its west is taking longer to move out of the way which has been causing some shear to be effecting Isaac..

You can see that the shear immediately around Isaac has been decreasing (another factor that will help strengthen Isaac. However..you also see an increasing shear area to the west but keep in mind that Isaac is not moving west but rather west northwest. However..once that ULL moves more out of the way that will decrease.

These three images are the convergence and divergence which the system is presently in excellent convergence and divergence and again this should end up helping Isaac to continue to organize and increase in intensity. The bottom image is just the shear image which confirms what we see on the tendency shear image. Around the system lighter shear versus west higher shear.

Movement..with the subtropical ridge in place this should mean that Isaac will continue to move on West north West tracking...eventually when reaching the weakness in the ridge ..Isaac should make more of a North turn... However..if the ridge remains stronger and the weakness weaker then this would continue Isaac on a West North West track ..

As far as intensity we see no real compelling reason for Isaac not to become a hurricane. We see no compelling reason for this to not become at least a Cat 2 Hurricane. We still feel potential is there for a Cat 3 hurricane as well.. The wild card in the scenario will be when the shear relaxes with the inner core organized it could be off to the races. We expect this to really start to strengthen about 12 hours from now and continue to strengthen until landfall.. Landfall will be anywhere from NOLA to MS/AL border. 
This will be a dangerous storm with very strong winds, heavy rain, beach erosion and flooding. If you have not done so yet make preparations for your home by boarding up all glass windows and if at all possible evacuate the region.

One more wildcard is that the ECM essentially stalls this out over New Orleans for 30 hrs. This would enhance rainfall and flooding if this were to occur.
Next update will be 24 hours from now!