Posted by wxrisk | GENERAL | Sunday 16 September 2012 12:04 am

1730  EDT  15  SEPT  2012


I suppose I probably should have posted on this upcoming pattern change a few days ago when it became apparent that the pattern was going to amplify and turn significantly colder as we came to the end of the month.  But I need a few days to recover from the intensely long and very active summer and hurricane season.

Over the past few days as I see more posts  and  forecast talk about the upcoming pattern amplification …I  have seen a lot of references to high latitude blocking developing with remarks such as    ”LOOK at the -NAO   that forms!. …”   As we will see shortly with the graphics and discussion… If you are reading comment from some of weather enthusiastic or weenie or even a professional meteorologist   in reference  a possible  g -NAO in the last week of September… then you are reading something from someone who doesn’t know what the hell they are talking about.

Over the past few days most of the model data has been showing the upcoming pattern amplification quite nicely.  The model agreement between the Canadian the GFS and the European model have all been pretty good since about Monday Tuesday (Sept 10–11).    At first some of the model data especially the European was developing a large cold    (cold being a relative term in reference to mid and late September)     HIGH over Northern Canada and dropping it towards Montana and the northern Rockies . But the European model saw the light and corrected itself back on Thursday and Friday ( yesterday)

Let us start by taking a look at the 12Z Friday operational European model with surface pressure and the 850 temps. We see two maps here but there both showing the same thing which is what the model says the day 10 surfacemao and 850 mb temps will look like on September 24. Now if this model depiction of the cold air mass coming south of the Midwest is correct this would bring about a killing freeze or frost for most of the Midwest on the morning of your September 24 or September 25.
This event is going to unfold essentially in three stages. The first stage hass to do with initial cold front which will be driving towards the Appalachian Mts and the East coast on Monday and Tuesday September 17 and 18.  Most of the model data shows the trough itself over the Midwest developing a slight negative tilt    ( the trough axis is aligned NNW to SSE)    which allows for the cold front to slow down and to develop significant showers and thunderstorms with it  as it   nears the East coast.
As a result the front will  see  an increase   in the amount of shower and thunderstorm activity. Right now it looks like the best thunderstorms and heaviest rains will probably be over portions of the eastern Great Lakes… northeast OH western and central PA… western and central NY state …then up into western or northwestern New England.    For the Middle Atlantic region the cold front   looks to be a fairly decent event but not a huge event.   There will be a lot of moisture flowing up the front from the large western Atlantic Ridge   ( the ” Bermuda High”)    but the really strong dynamics which brings about widespread severe weather will not be favorable for the Lower middle Atlantic regions.

This next map — the 12z GFS ensemble– shows quite nicely how this event is going to develop with 3 ” surges”.     The first surge as I mentioned above has do with the establishment of the deep trough over the eastern half of the CONUS and the INITIAL cold front the moves into the East Coast September 24   (the map on the left).     The SECOND surge of energy comes into the western Great Lakes and the upper Mississippi Valley SEPT 21 -22 but it still does not quite reach the East Coast and most of the cold air is still-   (the Middle map.)     And the 3rd SURGE comes into the Midwest and East coast and it is this third surge which finally reaches the East Coast on or about September 24  ( map on the right).

The  12z CMC  ensemble   mean is in strong agreement with the  12z GFS ensemble

Now if we take a look at the day 14 SEPT    day 9   runs at 4 12Z   of the European and the GFS side by side ….we see very strong model agreement.    We can clearly see several important hemispheric patterns on and this map.   Most prominent is the massive +PNA ridge which has formed over Western Canada into Alaska along with the very strong Aleutian low  ( -EPO).   And we can see the very strong Eastern Atlantic Southern Russia ridge which is often referred to in more popular terms as the Caspian Sea or Siberian central Asian Ridge.   When the -EA/ WR   Teleconnection is in the negative phase it can lead to +PNA development which is exactly the case here.

For those you that do NOT fully understand the Eastern Atlantic Western Russia pattern you can read about it here .
Now let’s talk about whether not this pattern has a negative phase of the NORTH ATLANTIC OSCILLATION.    The basic answer that THIS map for DAY 9 does NOT  show a -NAO.     This is one of these patterns which confuses a lot of people including some professional meteorologist you should know better but for whatever reason to exaggerated and HYPE things which don’t actually exist.
The red shading over the which barely pushes into southern Greenland is not and can never be counted as a -NAO.  Indeed if you look closely at this map you will see a deep 500 mb Low over Iceland… which by definition counts as a +NAO.    Instead what we are looking at here is a strong ridge   over the Northwest North Atlantic  Ocean… buts that all.
In the updated version from this afternoon’s modes… SEPT 15 valid day 9… we see even more proof that this is not in anyway a pattern that   features a  -NAO pattern.    We see a lot of dark red shading which represents strongly above normal 500 MB heights over the northwest Atlantic and the Canadian maritime provinces which barely touches southern Greenland.   And both the European and the GFS have a deep closed 500 Low located over Iceland!!!! Which again by definition can only mean you have a +NAO .

Next you can see a series of plots from Allan Huffmans’s weater Model page.  This first one shows the various weather models in the depiction of the coming strongly positive PNA pattern . And we can clearly see the all the models are in strong agreement.

Then we can see the next image which are plots of the EPO   ( eastern Pacific oscillation or the Aleutian Low) and again there is strong model agreement that the EPO is negative.

Now is the the NAO Plots.  And notice that none of the models are showing anything but neutral NAO… which makes a lot of sense given that we have someone above normal 500 MB heights over southern Greenland but also a closed 500 mb Low over a Iceland.

Now at this Point I am usually bombarded with questions about the CPC forecasts which have for the past several days been showing a distinct drop into the negative phase of the Arctic oscillation (AO) and the NAO  . I am sure that over the next 200 days I am going to have to make this point many many times:    the CPC plots / forecast for the AO PNA and NAO are essentially useless crap.     The reason for this is that CPC uses criteria that defines what the AO is… what the PNA is .. what the NAO is… that nobody else uses.
There are so many  cases of this happening that my computer hard drive sometimes cannot  fit them all.     For example there will instances over the next 200 days where the pattern on the West Coast is showing a  ”split flow”    but because of the criteria used by CPC the PNA forecast from CPC will show a strongly negative PNA or a PNA that turns strongly negative .

To see how this tendency often works we can look at the actual CPC forecast for the AO and the NAO and compare them to reality/ facts  . In this image we can see the forecast for the  AO /  arctic oscillation on the right hand side with the top chart on the right hand side showing the actual forecast.   As you can see as of September 15 it looks like the arctic oscillation is turning sharply negative. But we compare the CPC forecast of the AO at 7 Days… 10 Days… and 14 days..   The tendency for CPC forecasts to overdo the AO to the negative phase is VERY clearly.

Looking on the right hand side is chart we can see this Bias  in the  CPC/ GFS  ensemble  forecast very clearly.
This is also true with the NAO / north Atlantic oscillation pattern.   As we move deeper towards November and the heart of the winter …the negative bias or anomalies that the CPC forecast shows now at day 7 day 10 and Day 14 … will become quite  strong.

On last issue to discuss and tha has to do with the 12z sept 15 Run of the European model developing a fairly significant LOW pover the southeast US SEPT 23.   Now as we discussed above the models from this morning and yesterday were not showing this feature of the new European model has a strong piece of energy in the southern jet stream over the lower Plains on the morning of September 23. ( again this feature was NOT there on the earlier or previous model runs.   This feature merges with the new piece of energy — SURGE #3 as I discussed above— which I have highlighted with the capital “B” over South Central Canada. Some 48 hpurs later (Day 10)… the 2 systems Merge or ” phase” into one system over the East Coast …. Note surface Low tracks from SC to VA .

The 12Z SATURDAY Sept 15 run of the GFS has no such southern stream feature but given that it’s past 180 hours is often the case that the GFS simply does not detect energy in the southern jet stream until you get within 144 or 120 hrs.


Posted by wxrisk | GENERAL | Saturday 15 September 2012 7:02 pm

2300   EDT  SEPT  15   2012 

One of the best scenes at all the  STAT TREK  movies occurs in ST #6…  titled  The Undiscovered Country “.   In this movie   Captain Kirk  …Captain Spock …. Scottie ….Dr. McCoy…  Sulu  etc have discovered a conspiracy between some Stra Fleet Federation officers and some Klingon officers who don’t want a peace treaty go through and  are out to disrupt the peace conference.  There is a prototype Klingon “bird of prey”  starship that can also fire while it  is invisible   so while Kirk  and the Enterprise are battling …  or  trying to   battle …the  invisible Klingon warship.  The Enterprise is taking a real pounding so they come up with this idea to fire a Photon Torpedo  that is  altered   so that it  can track   the heat energy coming from the  Klingon  warship  exhaust.    As  Spock and McCoy  feverishly work on this torpedo.  Finally out of outrage or frustration   Kirk calls out to  to Spock … ” where is that Damn  Torpedo?”

As we leave the summer and move into autumn I am reminded of that movie because we keep looking for the photon torpedo   -   the  damn El Nino– and  it continues to not show up.

As has been discussed before and is well documented  El Nino Summers and Autumns strongly correlate to Below Normal   (and sometimes Much Below Normal)   hurricane activity and    Below Normal temperatures  with Above Normal rainfall over portions of the Plains and the Midwest.  Well you don’t have to be a weatherman to know which way this is going….

We are experiencing another near record or above normal hurricane season and we have experienced  a extreme widespread historic heat and drought across most of the country east the Rockies over the past 4  months.  When we we each the   “J” storm two weeks ago in the Atlantic   ( Joyce)  it was the second earliest  on record that the the 10th named storm  has  EVER developed.    Only exceeded by the historic 2005 hurricane season.  So clearly  all of  the early Hurricane seasonal forecast for below or much below normal hurricane activity has NOT  worked out.  And of course we all are very well aware of the extreme heat and drought we saw over the Summer months.  ( really the warm dry pattern took over last Winter  and   in the Spring).

So again the issue remains why hasn’t   the  El Nino  developed as we thought …?  And for you winter weather lovers and fanatics out there the correlation between  Weak  El Nino events   and  active and snowy winters over the central and eastern CONUS is well established .  So the refusal of the   El Nino  to take  over Has  significant implications those of us who like and enjoyed the winter months.

In other words  ” SPOCK!!! ….  Where is that Damn Torpedo!?”…
The SOI   tell us a lot .  This chart from the Australians shows the plot of the SOI over the past two years.  To briefly review this chart when the SOI  — in this case   it is a 30 day moving average–  is  at or lower than  -8 to -12   El Nino conditions are about to develop and what it drops for sustained period of time  below  -12    EL Nino conditions are underway and should begin to  develop  within the overall atmosphere of patterns within  next two weeks.     When the  SOI  is  in POSITIVE  territory… at  + 8 to +12    over a 30 day  period… La Nina conditions are likely to develop and once it moves in a sustained +12… La Nina conditions are likely to take over.

As we can see from the chart since the beginning of the Spring 2012   the SOI   has    dropped  to   around  -10  or so  (the threshold for El Nino)   only to  SUDDENLY    stop then   Jump   back   “up”   reaching either the neutral  Line  ( zero)    or   just barely reaching into positive territory .  As I have highlighted in this graphic we can see that  SOI  has done this  3 times   since  APRIL  2012

This movement tells us a few things.  First as long as the  SOI is doing this   there can be  NO   EL NINO.  Yes in the   technical sense the   warm SSTAs    in  ENSO  region   3.4 but the point here is that  we are NOT seeing anything   like El Nino  weather patterns   and  we have NOT   at any point since  APRIL 1.

This movement of the  SOI …  bouncing Up and down like that …is happening for particular reason.  It is not random and it is not noise. Something in the atmosphere is causing or suppressing   the  SOI  and   FORCING   this sort of movement.


Without getting too technical  the GWO  — global wind oscillation– is essentially a  index  that has been developed by researchers which tells us where the main  ” energy”  is located in the earth’s atmosphere.  This energy is refer to as the AAM  or the atmospheric angular momentum .  The atmosphere flows much faster at the equator and it does at the high latitudes and up towards a North Pole….  simply because the earth is much bigger at the equator that it is at the poles.  However the existence of a large mountain  ranges  on the planet   affects   or  altars  this  uniform  flow  of the atmosphere and these perturbations affects the overall   weather patterns.

The GWO   is similar to the MJO in some ways but there also some or differences.   The MJO develops through tropical convection  forcing which spreads   energy  out into the mid-latitudes from the equatorial regions.  The GWO is based completely within the mid-latitudes and is not tropical.


This chart shows the recent plots  or  movement of the GWO.  As you can see  the GWO has been located since  the SPRING  2012  over the bottom of the  chart stuck in a repeating loop going back and forth from left to right.  When the  GWO is over on  right hand side of the GWO plot  ….the overall patterns across the world are much more favorable and supportive of El Nino. When the GWO  is   over on the    RIGHT  side of the   chart… the  pattern is much closer to what we would see during a La  Nina.

This is the key to understanding  WHY  the SOI keeps bouncing up and down back and forth and never staying in the   El NINO threshold.  Because the GWO is stuck in this repeating loop….  Swinging from left to right and back from right to left…   the SOI   can never stay a located in the negative zone to trigger a El Nino type of weather pattern.

This chart shows a another way of looking at the  GWO / AAM.  If we were to take that long complicated twisting back and forth  motion of the  GWO…  and pull out into one string….  we would have the  AAM chart .  Again without getting too complicated  for North America   the   LOWER or more negative the  AAM the warmer and drier the pattern is likely to be for large areas of North America.

Note that back in late JUNE  and JULY   of 2012 the AAM reached a extreme low value and that is why we had the extreme heat which dominated much of the country this past summer.

So to answer a question from Captain Kirk…   “SPOCK  where is that Damn El Nino.?..“….  until the AAM moves above the neutral  line into positive territory… the GWO will continue to stay at the bottom of the chart and stopping a looping pattern back and forth from left to right and right to left.   And as long as the GWO continues to do that… the SOI   will NOT   lock into a  sustained   negative values  to  Trigger  El Nino  pattern….  And without the  SOI locking in….  the El Nino  will NOT   develop.

Of course this has    SERIOUS  implications   for the Winter and  any  Winter 2012-13 seasonal  forecast  for North America. Most of these   EARLY winter forecasts are   based on the idea of  WEAK   El Nino developing.  Based on that assumption  a forecast  for a colder  than Normal and / or Snowier  than Normal  Winter 20102-13  for the central and eastern  CONUS  makes some sense . But to drive home the analogy… the GWO   stuck in this current pattern the   Invisible   Klingon   BIRD OF PREY  warship and we wont  make it to the   UNDISCOVERED  COUNTRY  – winter of 2012-23-  without  that  damn  Photo  Torpedo.  It is  still   early  but do NOT   blindly  make this assumption  the  weak El  Nino is coming.



Posted by wxrisk | GENERAL,HURRICANE SEASON 2012 | Monday 3 September 2012 11:32 pm

2130 EDT   SEPT  3  2012


One of the things that really bothers me about hurricane forecasting is the  bit of wisdom or  wise tale that suggests that hurricanes  have   “minds of their own “….as if   they  were people. That    ”saying”    has been used for many many years because of the poor understanding of the atmosphere we used to have with respect to the all tropical cyclones. But it’s not really accurate to still make that claim.  Hurricanes do not have minds of their own … they obey the laws of physics.
Now that doesn’t mean we always get the hurricane forecast correct. All sorts of things can happen in the last 60 hours before landfall and Isaac is a pretty good example of this.    That being said let’s talk about Leslie.    Back on Friday night I posted this over on the face book page and it’s a pretty good place to start.

***ABOUT LESLIE… A THREAT TO EAST COAST?… No it will not be… well *PROBABLY* not.. First as I said several days ago LESLIE will NOT be a early week curvature storm ( when many other were sayung Just that) .   Once she clears 60 degrees West longitude  and passes  well north of Puerto Rico..   then typically   after turning due North …  most  Tropical cyclones this would typically go out to sea probably east of Bermuda .  BUT with Leslie SHOULD a major ridge will form over the central North Atlantic early next week…. which essentially will trap  or block   LESLIE   preventing her from going out to sea.   As the ridge in the jet stream expands she be FORCED s-l-o-w-l-y westward… Towards the EAST COAST!!! sounds ominous, no?
Coming out of Labor day …. all of the weather models show a very IMPRESSIVE trough developing over Midwest and the East coast . Now TYPICALLY most major troughs like this in the jet stream force any hurricane in the western Atlantic back out to sea. That is PROBABLY what will happen here with LESLIE. The data shows LESLIE coming west BUT at a rather high LATITUDE. Thus the trough (as it sweeps through the Midwest and the East Coast ) Kicks LESLIE e out to sea SEPT 8-9
BUT there have been a few RARE but well known cases where there is a big trough over the Midwest / Appalachian mountains and the hurricane interaction is JUST the PERFECT position so as to “GRAB” the hurricane and pull it TO the coast…. See for example the great east coast Hurricane of OCT 1878. ..the 1938 hurricane… The 1933 Chessy bay cane… HAZEL 1954 and ISABEL 2003. These sort of “uncommon” cases ONLY occur when the hurricane is SOUTH of 30 north latitude AND … AND enters the trough base in the SOUTHEAST SIDE side of the trough. As   of right now … no data shows this right now. When Leslie begins to maker move towards the coast she  comes in  s much further north then 30 N latitude.

Well here we Monday afternoon evening and that analysis still apparently holds true.  I am not at all surprised by the constant Westward  d adjustment of Leslie.   Once again we have a problem with the hurricane models because they are run off the GFS grid.    As I stated many times once you get a tropical cyclone north of 30° north latitude the cold bias of the GFS model which tends to overdo develop troughs   and/ or   phase two different  into one big system ….really begins to come into play here.
It is these very reasons why the GFS model consistently took Isaac into Florida and up the East Coast for many many model cycles until finally getting a clue 72 hours before landfall.  We are seeing the exact same problem here with a hurricane models and how they are handling tropical cyclone Leslie . It is no surprise that the model which does not have the cold bias — the European model– has been further west than any other model with the track of Leslie and so far has the best overall accuracy score with regard to the track of Leslie.

Broadly speaking one cane to break down most East Coast hurricane events into three groups.

  1. The first group pass to do with the curvature between the East Coast and Bermuda. This sort of track is refer to by the old timers as a   “SLOT HURRICANE:“.
  2. The second group refers to the typical East Coast landfall track… where the tropical cyclone essentially goes along the coast following the path of least resistance usually making landfall at or near Cape Hatteras and paralleling the Middle Atlantic and New England Coast up towards Cape Cod. This group can be referred to as the EAST COAST TRACK. Most East Coast hurricanes fallen this track and we can refer to a few them by name to give you a general idea. Hurricane bob in 1991… Hurricane Gloria 1985… Hurricane Floyd 1999… Hurricane Irene 2011 hurricane Belle 1976.
  3. The third group is a lot less common but far more dangerous which I refer to as the NW TRACK. Some are more dangerous and historic East Coast hurricanes are in this group…. Such as the September 1938 New England hurricane… Hurricane hazel… Hurricane Donna… Hurricane Isabel Chessy bay 1933 Hurricane just to name a few.

By looking at a few of the cases we can see what exactly is   the  threat is with regard to Leslie.

First let’s take a look at the typical East Coast hurricane track. This first image refers to hurricane GLORIA   in late September 1985.    This was the first big hypermedia event at the dawn of the new electronic age in media. In this image we can see the actual track in the black it background image.  And we can see below that the upper air and surface maps explaining WHY Gloria which was forecasted come inland over New Jersey and New York City in fact did not come inland but paralleled the coast. On Thursday, September 26, 1985    the upper air map showed a major trough over the Midwest that was positively tilted (SW to NE).    And on the surface map we can see Gloria approaching the Southeast U.S. Coast. It was thought that the trough would deepen and take a negative tilt (NW to SE) which would pull Gloria it into the coast .   Instead the Midwest trough did go negative BUT the trough did NOT deepen ( plunge south) .    Thus the Midwest   trough  acted as a ” KICKER”     which forced Gloria to stay on or just off the coast

Next   let  us look at hurricane FLOYD   September 1999. In this image we can see the actual track which was very similar to Gloria from 1985. The upper air map shows a deep trough over the Midwest but the trough is positively tilted ( SW to NE). And on the surface map and the upper air map we can see Floyd just off the Florida coast.    We can clearly see that from this position the trough is only going to act as a kicker and not allow Floyd to come inland . Which is exactly what happened.  The rains over Eastern North Carolina and Eastern Virginia were torrential and historic flooding occurred but Floyd did not come inland.

We can   look briefly at HURRICANE EARL from 2011.   Here is the upper air map and again we can see very clearly are pretty big  trough over the Midwest and EARL off the Virginia North Carolina Coast.    The problem is of course at the trough is “progressive ”     —that is to say moving from west the east and it is NOT  deepening.    So it drives EARL off the coast which is exactly what happened.

Now it’s compare that to some of the more famous East Coast hurricanes and see what difference is we can detect.

We will start out with the most famous of all East Coast hurricanes which arguably might be the September New England hurricane of 1938. In this image we can see the actual cape verde classic hurricane track…. which is quite impressive in his own right.

In this next  image we can see the actual surface track and the upper air track from the early upper air maps which were available at the time.    The key point here is that there was a massive trough over the Midwest but unlike what we sought with GLORIA EARL or FLOYD …  this trough was actually deepening as opposed to moving from west the east.   That is to say the trough was actually driving down    towards Alabama and Mississippi as opposed to sweeping towards East Coast.

This is critically important because it changes the entire pattern. With a trough a deepening towards the gulf coast it allows the the western Atlantic ridge ( “Bermuda High”) to expand the get pulled towards the coast and this in turn force is the hurricane to move into the coast as opposed to paralleling it ON the coast or Just offshore .

In this next example we can see the upper air and the surface Maps of mighty hurricane Hazel OCT 1954    which I think has been the storm of record for the East Coast outside of New England over the last 100 years.  In this first map of HAZEL’s approach to the East coast in mid October 1954 the upper air map shows a Upper Low embedded in deep trough over the Midwest .  At first glance it would seem a high probability that this large deep trough would easily knock HAZEL offf the coast and out to sea. But that is on what happens.

In this set of maps we can see that the upper air map clearly showed the West Coast ridge  over North America amplify — that is to say pushing    NORTH  towards the Yukon and Alaska.   This in turn allow the deep trough and the Upper Low to move from Wisconsin down into Tennessee!    This dramatic movement of course changes the entire pattern on the East Coast and over the Western Atlantic Ocean.    The trough deepening –as opposed to moving from west the east — allows HAZEL to be pulled into the trough.    The upper Low over   the Midwest  was so deep in itself that   in combination with HAZEL…   there was an extremely rare and rapid transition from hurricane to monster nor’easter which developed in a 12 hour time frame.    As a result HAZEL did not lose energy as she raced through North Carolina Virginia Maryland Pennsylvania and up into the eastern Great Lakes.

In our third special case we look at mighty hurricane Donna from September 1960 which was also a classic CAPE VERDE hurricane which did not behave as forecasted.  Donna pass north the Puerto Rico then turned due west passing between the Florida Straits in Cuba…. then taking a sharp right turn making landfall south of Tampa and warring up the East Coast.
In this first image we can see a ordinary looking trough in the Jet stream dropping into the Dakotas as Donna it is off the west coast of Florida.   In the middle map we can see that the trough is beginning to change and instead of moving from west the east across the great lakes we see a dropping down towards Arkansas.   This movement causes the pattern over the East Coast and the Western Atlantic Ocean to change…. by increasing the western Atlantic ridge and pulling it toward the East Coast.  In the third map … we now have a massive trough extending from the western great lakes all way down to Louisiana!   The trough has clearly taken on a ” negative tilt ” . Not surprisingly this is forced Donna on the coast and allowed the system to maintain much of its energy .

This next image shows mighty hurricane Isabel which was   major event for North Carolina and Virginia in September 2003. On the TOP map we can see the actual track of Isabel passing north of Puerto Rico and striking Eastern North Carolina and Eastern Virginia.    The middle map shows the upper air pattern as Isabel approach the U.S. east coast. We have a pretty deep trough over the Pacific Northwest and the northern Rockies and we have a very strong western Atlantic Ridge ( Bermuda High). The third map shows that the cause the deep trough over the Rockies continue to amplify as it pushed into the Midwest it caused he strong western Atlantic ridge ( Bermuda High ) to get pulled INTO the U.S. East coast.   Notice  here the THICK BLACK LINE which pushes all the way into Pennsylvania lake Huron and north of the state of Maine. Obviously Isabel only had one possible path which was to strike Eastern North Carolina Eastern Virginia.   Not surprisingly  h many of the GFS models showed a land fall further up the coast be cause the cold bias of the GFS showed a weaker Bermuda High.

So what have we learned?     There are plenty more cases here to show but what we have seen from the 1938 hurricane hazel 1954 and Donna  is that the tropical cyclone has to be in a certain position off the southeast coast at the time that a trough of the Midwest is dropping southward or deepening.    
If …on the other hand … the Midwest trough is progressive — that is to say moving from west the east — then you end up with a situation where the trough acts as a KICKER and drives the hurricane off the coast and out to sea.

As I stated above at the beginning of this essay … over the past few days the European model –especially last week –has been showing Leslie not being pushed out to sea but getting forced back towards NORTHWEST and int the general direction of the NORTHEAST US Coast because of a developing ridge in the jet stream over the middle of the North Atlantic Ocean.   For example here is the August 30 European run for day 9 and 10 and we can clearly see the model trying to drive LESLIE to the east coast to get around the developing BIg ridge in the North Atlantic.

The problem here is that even though we have a deep trough over the Midwest LESLIE is already    MUCH further NORTH than what we saw in the cases of the 1938 New England hurricane…. Hurricane Hazel and Hurricane Donna.

Not surprisingly today the 12z GFS Model   showed no change from it has been handling LESLIE.  The model shows an ordinary trough moving through the Midwest at DAY 6… which at the surface appears to be a ordinary cold front. These features sweep off the East Coast and drive Leslie harmlessly out to sea.   BUT  the  18z  GFS   takes a step towards the    12z  EUROPEAN  model solution  ( see  below)

However the afternoon European model continues to show a more ominous looking scenario and has a lot of people all excited. As impressive as the European model is as I stated above and quite clearly shown above in all cases where we seen a major East Coast hurricane strike… The tropical cyclone was located off the southeast coast below 30 degrees north latitude as the trough over the Midwest begins to deepen.
On the 12z MONDAY SEPT 3 run of the European model we can see the pattern set up at DAY 5-6. The model shows a much deeper trough over the Midwest the what we’re seeing on the GFS and not surprisingly be also see a stronger ridge out in the north Atlantic which prevents LESLIE from turning out to see. On September 9 the European model actually forms a large upper low ( ULL) over the Ohio Valley which continues to drop towards Georgia. This only increases the strength of the RIDGE in the northwest Atlantic… which in turn forces LESLIE to head towards the southeast coast of Massachusetts!!!!

on DAY 7 / SEPT 10 the European model shows this amazing ULL diving towards the Georgia Coast and in doing so shows a Fujiwara EFFECT taking place.    ( two fairly strong Low being very close to another one alters the movement and track of eash other).

Notice now that the RIDGE in the northwest Atlantic is pushed all way into Boston and New York City… Yikes!!!! According to the European model LESLIE would be located due east of Cape Hatteras at 35 N latitude and 70° W Lange to at an amazing strength of 922 MB which of course would be a historic category five hurricane.  This is a very likely to be way overdone by the European model.

DAY 8/ SEPT 11 this amazing and highly unlikely meteorological dance of death continues with the UPPER LOW reaching the Georgia South Carolina Coast and LESLIE striking very close to Cape Cod. Again the European model still has this intense hurricane at 930MB which is a very strong category four hurricane… Extremely highly unlikely.

And by day 10 the European model has a system striking Halifax nova Scotia with arguably one of the strong as hurricanes they have ever seen in that part of southeastern Canada.

The European scenario is extremely unlikely.. BUT   the Synoptics makes sense with with respect to the Upper air patterns that allow for Major East Coast hurricanes to strike and or come Inland.    The problem  with this scenario as I stated before is that Leslie is not coming INTO the U.S. east coast at a fairly far south latitude… which was the case with the 1938 New England hurricane…. Hurricane hazel …hurricane Donna and hurricane Isabel in 2003.
At this point in time I can not completely rule out the European scenario but in order for the European to work out we must see a large trough over the Midwest drop into the Tennessee Valley… preferably with a large upper low forming over Tennessee and Georgia. Only if that happens would be European scenario be viable. There is no margin for error here…. ANY change in the European scenario would mean that LESLIE would stay further off the coast