Wet and Chilly Pattern In Store For Most..

Not sure if any one has noticed the same thing that we have seemed to notice and that is that it seems that we awfully quickly have gone from what was a warm to very hot pattern to an unusually early fall type air mass. September so far seems to be a completely different month compared to the prior months..

Now lets show you what we are talking about before we get into the very above image. Lets look back at July And August across the Northeast Region..

You can clearly see that these two months were pretty much well above normal in the Northeast but from Central PA to the southeast it was normal to below normal..
Fast Forward to september...

Here it looks pretty much like we are almost back into looking like a warmer pattern with the above normal temperatures but ..we need to look at the last 14 days to get the brighter and full spectrum of the picture..

The last 14 days..NOW that is the big change we were talking about ..but look at the last 7 days..

Even more below normal especially Ohio region into eastern KY and parts of West VA. Pretty stark drop and contrast in temperatures compared to even just the first week of September...
So we have gone from a warm to hot weather pattern to a chilly air mass and a air mass that will be becoming more increasingly wet across the central part of the nation.

Now as you can see we have a cold front dropping down from the north but to the south of that we also have another frontal feature with a warm front extending south and this low pressure is going to more or less be moving towards the east at the same time the cold front will be dropping to the south and this is going to increase the likely hood of rain (some of it heavy) and the potential for severe thunderstorms over the next 72 hours.

From there this frontal system moving in from the NW will be making its way into eastern PA in the over night hours on tuesday after midnight (which would mean early wed Morning)..

Over all we are expecting any where from 1 to 3 inches of rain with isolated areas up to 4 inches of rain. Many of these areas need the rainfall as they are having harsh droughts at the present time.

As we mentioned this will be moving into E PA and NJ by late tuesday night which will introduce a chance of heavy rain in those regions as well..

It does appear however that ridging in the long range could build back west from the Central Atlantic ridge to the Western Atlantic ridge into the Eastern US so if that be the actual outcome we could see warmer weather return just in time for October...

September 18th Severe Weather Outlook...

September 18th Severe Weather Outlook...

While instability is NOT going to be off the walls and only meager at best ... Energy Helicity Index is on the impressive side ..Helicity Is on the impressive side and in addition to this SHEAR is o

n the impressive side..
Lets look at shear first ... we are going to look at 21 hours , 24 hrs and 27 hrs..and you can see that the shear goes from 30 knots to 70 knots +
http://www.twisterdata.com/data/models/nam/221/maps/2012/09/18/00/NAM_221_2012091800_F21_SHRM_500_MB.png
http://www.twisterdata.com/data/models/nam/221/maps/2012/09/18/00/NAM_221_2012091800_F24_SHRM_500_MB.png
http://www.twisterdata.com/data/models/nam/221/maps/2012/09/18/00/NAM_221_2012091800_F27_SHRM_500_MB.png

So what this implies is that severe potential can indeed occur in the over night hours (despite unfavorable timing)

Here is the EHI
http://www.twisterdata.com/data/models/nam/221/maps/2012/09/18/00/NAM_221_2012091800_F21_EHI_3000_M.png
You can see EHI is as high as 2-3 over East Central PA ...and at or above 1 in other areas..
HELICITY
Helicity is 350 + to 550 + ..
http://www.twisterdata.com/data/models/nam/221/maps/2012/09/18/00/NAM_221_2012091800_F21_HLCY_3000_M_ABOVE_GROUND_0_M_ABOVE_GROUND.png
CAPE as we mentioned is meager with only about 500-1500
http://www.twisterdata.com/data/models/nam/221/maps/2012/09/18/00/NAM_221_2012091800_F21_CAPE_SURFACE.png
Lift Index only to about negative 4
http://www.twisterdata.com/data/models/nam/221/maps/2012/09/18/00/NAM_221_2012091800_F21_PLI_30_0_MB_ABOVE_GROUND.png
Dew Points will be in the 60-70 degree range...
http://www.twisterdata.com/data/models/nam/221/maps/2012/09/18/00/NAM_221_2012091800_F21_DPTF_2_M_ABOVE_GROUND.png
Temperatures will not be overly too warm 70s to around 80 but the dewpoints are high so it will feel ..sticky outside..
http://www.twisterdata.com/data/models/nam/221/maps/2012/09/18/00/NAM_221_2012091800_F18_TMPF_2_M_ABOVE_GROUND.png

What is going to be responsible for this is a very strong cold front coming in from the west. There will be strong winds out ahead of this front as well in addition to the severe potential which we explain with the map above...
http://www.hpc.ncep.noaa.gov/basicwx/92fwbgus.gif

In addition to the above will be heavy rains on the order of 1 to perhaps local areas of 3 inches..If we are able to get some more sunshine in early in the day this would add on to the instability available but with the shear, helicity and EHI at impressive levels we urge people out and about to keep there eyes to the sky...

We will be here all day monitoring conditions and posting watches etc ... and we will also be out filming whatever may effect our particular local area...

Invest 91 L Update # 2

At this present point and time we think that Invest 91 L is probably a depression judging by the following information :  

Wind (1 min. avg.):

30 knots (~35 mph | 15 m/s | 56 km/h)

It is clear though that 91 L is still suffering from dry air but this does look better then it did just a few hours ago .. This is what it looked like a few hours ago..

The other thing that we still do not like with what is going on though with 91 L is the shear is increasing all around the vicinity of the system. Whenever you have this combination you have a slower time in developing the inner core.

Shear is generally on the order of 10-20 knots and you can see generally the increasing wall of shear around the system.

You can see the dry air on this image ..and then the other thing is that the voricity is very stretched out and elongated which you will also see on the image below:

This just means or implies that it will take longer to develop that center of circulation and tighten up and intensify.  Convergence and divergence is actually decent across the area. So this is one contributing factor to the positive for development..

So..the environment is not exactly conducive for any kind of rapid intensification but rather a slow intensification. As far as movement ..general movement for now should continue in a west to northwest basis based on the steering currents..

However..we still feel highly confident that this will not have any effect on the East Coast or anywhere near the USA. This storm should stay out over the Atlantic....

Guidance shows this very thing happening and occurring..

We still also think this will become the 14th named storm of the tropical season . However..as stated this will not have any effect on landfall but rather one for the fishes..

Next update 24 hours from this morning! 

Invest 91 L ... Tropical Outlook

There  is not much doubt in our mind that Invest 91 L is going to develop. However, there is also not much doubt in our mind that this system will have no impact on the USA. 
Essentially this would be due to Tropical Storm Leslie and also Hurricane Michael which have both beaten down the subtropical ridge.  In other words both Leslie and Michael have created a large weakness with in the ridge...
While the steering currents suggest for 91 L to continue moving off to the west north west..once it comes to that weakness it should start to make a northerly turn.. You can see that weakness by looking at the steering currents..

At the present time there are only two factors which could hinder development . First one is the dry air ... and then the second one is increasing shear ..even though at present shear is only 5-10 knots ...

Presently there is decent convergence and divergence across the system...

We think the odds are pretty likely that this will become a tropical depression within the next 24-36 hours and probably a tropical storm (Nadine) by about friday... 

Pretty much this is the track that we are expecting for 91 L to take .. 

Quick look at the guidance with the GFS at 144 hrs 

ECM a little less enthusiastic about development then the GFS..

GGEM is more in line with the GFS ..

So in summary we feel the environment outside of some dry air , which does not seem to be effecting the system right now ..and some increase in shear..is marginally conducive for development and we should see a tropical depression form in the next 24-46 hrs. There after we think this will become NADINE but because of the weakness in the ridge this will recurve out and stay in the Atlantic with no threat to land...
We will update this in 24 hours from this Update...

Brief Update On Tropical Storm Leslie

There is really no change to our forecast track on Tropical Storm Leslie.  Latest guidance pretty much supports our thinking track wise. The biggest question becomes Intensity.  We have been talking about how Leslie is quite large in size and when a tropical cyclone is so large in size it takes considerably longer for the center of circulation to contract and tighten up. And you can see from looking at the wide view of the water vapor that this continues to be the case..

However , another thing that you can tell by looking at this image is that Leslie continues to suffer from dry air being entrained into the center of the circulation. You can also see this when looking at the water vapor close up as well as the visible satellite image..

You can see that the system is very disorganized at the present time. The system should generally continue to track off to the north as it is moving along the western edge of the subtropical high pressure..

As you can see on the currents above you also can see a large trough over the eastern USA which this will be moving out into the Atlantic. As this moves off the eastern coast it will cause Leslie to speed up more and then eventually start to move towards the NE...

Now while presently there is only 5-10 knots of shear around the center ..the outer bands are in higher shear and as the shear tendency map shows shear is increasing to the north of the system... Combine this increasing shear along with the dry air still being entrained into the system and we think that the window becomes very small for Leslie to regain hurricane strength.. Another reason that we feel the window is small is that while the water temperatures are still warm enough to support strengthening ..the Tropical Cyclone Heat Potential is really lacking around 30 N and above..

Looking at the guidance tonight ..It seems like the GFS and GGEM are in agreement with the tracking of the system making landfall in New Foundland ..

And while we do not have the ECM in 6 hr increments but only 24 hr increments we can show you  hour 48 and it seems to pretty much be in agreement as well..

So in summary we feel that the atmosphere around Leslie still remains a bit to much on the unfriendly side for any real further strengthening. TCHP is low .. Shear is increasing north of the system and dry air is still effecting the system and the largeness of the system itself is not allowing the vorticities to become vertically stacked or aligned. 
Less environmental conditions change we do not think Leslie will regain hurricane strength. NHC has the latest pressure at 988 mbs which is up 3 mbs in pressure. ADT has this pressure significantly higher at 997.6 and visible and water vapor images are showing a system being effected by dry air and shear...

Tropical Storm Leslie- What happened to regaining to Hurricane strength?

That right there is the question that we want to address first thing in this over night discussion. If you recall from past discussions we talked about that Hurricane Leslie would be weakening.. and right on time that indeed did happen and ended up being the case.. Just as of 15 hrs ago approximately NHC issued this as there 11 AM advisory...

LESLIE WEAKENS TO A TROPICAL STORM BUT FORECAST TO REGAIN HURRICANE STRENGTH...
11:00 AM AST Fri Sep 7
Location: 26.8°N 62.2°W
Moving: Stationary
Min pressure: 981 mb
Max sustained: 70 mph

Well folks , it does not take a rocket scientist to discover that this has NOT happened.. We have not regained hurricane strength... and as of 2 AM.. we find this...

LESLIE MOVING SLOWLY NORTHWARD...

2:00 AM AST Sat Sep 8 Location: 27.8°N 62.3°W Moving: N at 3 mph Min pressure: 983 mb Max sustained: 65 mph

Matter of fact instead of strengthening it had weakened further and again this was something that was NOT anticipated on the National hurricane Centers part.

Well the problem comes in two fold .. 
1. Models are not coupled with the ocean , at least not global models..So what this means is that because Leslie is essentially stationary to barely moving for quite some time it has upwelled cooler waters. We mentioned this past couple updates and this is something that models do not take in to account when we look at the intensity they are showing..
2. We mentioned the size of the system and the fact that it was not and still is not vertically stacked would mean that this system would have trouble developing. 
3. We have also pointed out the dry air that has been effecting this system.
4. We have also pointed out that shear was still a problem and as you will see continues to be a problem ..
5. Leslie is caught in week steering currents...

The intensity forecasts on this system have been pretty bad ..this simply says to me that the science is not yet at the point where it can accurately forecast intensity of Tropical Cyclones and more study has to be conducted into this. 
So lets look at what is presently happening with Leslie now... we feel that the current environment is a lot more important piece of the forecasting tool then the actual guidance...

Very first thing we are going to look at is the visible and the water vapor images. The wide view just shows you how large this system  is and remember the larger a system is the more difficult and longer time it takes for the center to contract and the system to intensify.

The next thing we need to notice is all the brown color on the bottom image on the left side of the image and to the south of the image. What this tells us is that dry air is still being entrained into the center of the circulation and the visible shows this process very well..

The next thing we are going to look at is that the 700, 500 and 200 mb vorticities are still not vertically stacked...

Diving even more into the atmosphere is looking at the shear..and the models were actually forecasting for shear to DECREASE... Instead let us see what we have occurring..

This shows that over the northern part of Leslie that the shear is anywhere from 10 -30 knots. Again.. ideal shear environment for strengthening is 5-10 knots..Anything above will cause the system to develop a lot more slowly if not curtail development. Factor in the dry air and you can see why this has not strengthened but only been weakening and maintaining.. But lets look at the shear tendency map to get the total picture..

Remember we are moving slowly , barely north and to the north and west and east and south there is nothing but increasing shear...

The only thing that continues to pretty much lay in favor with this system is the convergence and divergence continues to be decent across the system..

Now you can see where ADT puts the center location and this system has barely moved thru out the course of the day.. You can especially see this if you check out the loop in motion..

So as you can see the environment continues to not be to friendly for further strengthening and this may have trouble strengthening while it is over colder waters from up welling. Once it starts to actually move north it could potentially develop further but with the increasing shear that may end up once again hindering the development..

00Z Guidance essentially is all now in agreement on a track just east of Nova Scotia. However, there are some timing issues still involved..

So in summary the atmosphere or environment around Leslie is really not conducive to strengthening at this point and time. The movement will continue to be very sluggish and slow and may meander north and south etc over the next day or two because of the mid level ridging that is to its north. Then .. at some point the trough will be coming off the east coast and this should start Leslie to begin taking a more NE track.
By the time this system gets to the Nova Scotia and New Foundland regions this should be an extratropical cylone. IF the SHEAR does not let up as forecasted there is the potential that any strengthening could be further delayed and we do not make it back to hurricane status...So this is something we will have to watch.
No change in track forecast that was issued and next outlook will be in 24 hrs from now!
Have a great night!