Tracking Jose...Does Southern New England See Any Impacts?

With regards to (at the time of this writing) Tropical Storm Jose, I personally, may end up eating my words.  This week during my broadcast at school, I briefly touched upon Jose and I stated Jose would pose no threat to southern New England.  Well over the past several days really computer forecast models have been further indicating that not only will the beaches and coast see impacts from high surf but a good chunk of the region may see strong winds and heavy rains from Jose.  While this probability is on the table there is still a great deal of spread within the computer forecast models with regards to the exact track and there is still that possibility that Jose moves on out to sea with no impacts with the exception of high surf and swells.  In retrospect, do I, or should I regret my choice of words and be so quick to dismiss the possibility of an impact from Jose?  I guess the answer to this is yes and no.  These days in weather there is so much hype and this hype comes from numerous sources.  You have hype from some TV stations and this hype is generated to increase their ratings (higher ratings means more money), you have hype from hobbyists and people who study weather.  This is done to draw attention to themselves and get more "followers" on their social media platforms.  Then you have people who just base forecasts off each and every single model run.  This right here is not forecasting.  Forecasting is more than just looking at each model and each individual model run.  Forecasting is understanding persistence, understanding atmospheric patterns, understanding biases within each forecast model, understanding climatology and understanding what types of patterns can correlate to certain outcomes.  It is very difficult to get tropical systems to directly impact our region and there is a good reason for that.  It takes a very special weather pattern and a very specific interaction of numerous ingredients for these scenarios to happen.  Anyways, I'll end the long rant and we will look into all the specifics and what we need to watch for over the coming days with regards to Jose and where Jose may track.

The 5:00 PM advisory from September 15th by the National Hurricane Center (NHC) has Hurricane Jose just past the threshold between a tropical storm and a category 1 hurricane with maximum sustained winds of 75 mph (A tropical storm is classified as a hurricane when maximum sustained winds reach 73 mph) and well north and east of the Bahamas.  The cone of uncertainty indicates well...a great deal of uncertainty with the potential track.  The potential track ranges from a very close call with the east coast of the United States to a track well east of the United States.  Notice as the forecast position of Jose changes with each day the cone of uncertainty grows larger.  This is not all that uncommon, however, it is uncommon to see such a large spread.  This is due to the fact that the computer forecast models are really struggling with the track of Jose.  The reason for this is due to how the upper air pattern evolves over the next few days and this is something we will explore within this post.  Also notice that the NHC does expect Jose to re-strengthen back into a hurricane as denoted by the "H" within the track but they also forecast it to weaken back to a tropical storm as denoted by the "S":

 Exploring why the cone of uncertainty is so wide we will look at the latest ensemble means from this morning's runs of the GFS and European computer forecast models with the GFS on the left and the European on the right.  Each of those individual tracks are different solutions projected by each member from within that computer forecast model.  These maps are often referred to as "spaghetti" plots because they resemble that of spaghetti:

If these look messy well it's because they are.  What we can gather from this, however, is that there is rather strong consensus that Jose will come relatively close to the east coast, the question just is how close and what happens to Jose when nearing the east coast.  Some members bring Jose close enough to provide some impacts while other members just turn Jose right out to see, likely with minimal impact.

Before we explore further, you're probably wondering if we do receive direct impacts from Jose will it be a hurricane?  The answer to this question is it is very unlikely and there are some reasons for this.  For tropical storms to become hurricanes and become strong hurricanes they need 3 key ingredients; they need to traverse over very-warm ocean waters which have sea-surface temperatures of at least 80F or higher, they need to be in an area and move into an area of relatively weak wind shear aloft (strong wind shear tends to disrupt the circulations of tropical systems), and they need to be in an area of high moisture content (if dry air is drawn into the system the system will weaken).  We will first look at sea-surface temperatures (in degrees C) as of yesterday across the western Atlantic.  I have circled two areas.  The area circled in red will be waters in which Jose will move through.  Correlating the colors to the color bar at the bottom we are looking at water temperatures which range from about 27C to 29C or 80F to 84F.  With what I mentioned above, these water temperatures are certainly supportive for Jose to not only to keep its current strength but are supportive for some further strengthening.  The second circled area is water temperatures off the the Carolina coast extending northward along and just off the New England coast.  Water temperatures here are in the 20C to 22C range or 68F to 72F.  Obviously these temperatures are far below the 80F threshold.  This is one factor which will inhibit Jose from being a hurricane if it were to make landfall or come very close to our area:

    
We will now explore the wind shear over the western Atlantic.  On the map below, the green contours indicate areas of favorable (or weaker) wind shear (favorable meaning increased likelihood that a tropical system will strengthen) while red contours indicate areas of unfavorable (or stronger) wind shear (unfavorable meaning an increased likelihood for weakening).  I have circled where Jose is positioned currently.  Notice how Jose is in an area of favorable wind shear.  Also notice, however, Jose will be moving into a widespread area of much stronger wind shear:

Thus far we see that not only will Jose be lurking into much colder waters but Jose will also be lurking into an area composed of much stronger wind shear.  Two factors which will prevent Jose from being hurricane status if it were to come close to this region.

Finally, let's explore moisture content over the western Atlantic and to do this we will look at a current snapshot of water vapor imagery.  I have circled 3 areas where drier air exists.  The biggest area of interest is drier air working over much of the continental United States and some drier air east of Florida.  There is also some drier air to the east of Jose.  There is a possibility that some of this dry air could work into Jose and if that happen further weakening would likely occur:

Now let's discuss the upper air pattern and how the upper air pattern may evolve over the United States and Atlantic Ocean over the next several days as this right here is what will ultimately determine what path and track Jose will take.  The first thing we will look at is the projected forecast of what is known as the Pacific-North American teleconnection pattern (PNA).  The evolution of this teleconnection pattern strongly correlates to the development and evolution of the upper air pattern over North America.  This index has 3 phases; positive, negative, and neutral.  When the PNA is positive, this correlates to a trough (dip in the jet stream) across the eastern Pacific Ocean extending into western North America.  The result from this is a ridge (northward build in the jet stream) across the eastern United States extending into the western Atlantic.  The negative phase is just the opposite with ridging across the eastern Pacific extending into western North America with the result being a trough over the eastern United States extending into the western Atlantic Ocean.  When the signal is very weak the PNA is deemed to be neutral.  Currently (as shown in the image below) the state of the PNA is just all so slightly negative, however, it can be considered neutral.  Over the coming days, however, as ridging builds into the Gulf of Alaska this will result in a trough amplifying (or strengthening) across the western United States.  This will result in ridging building into the east coast and the PNA will become further negative:

This is typically not something you look for when talking about the idea of a tropical system working up the coast.  What you preferably want to see if this trough out in the west amplifying as it moves through the central part of the country and really amplify in the vicinity of the Ohio Valley region.  You also want the trough to begin taking on what is called a negative tilt (we won't go into details on what that means now since this post is already long enough) as the system is beginning to take a turn up the east coast.  When these conditions are met the trough does what is called "capturing" the system and enhances the likelihood for the storm to either hug the coast or make landfall along the coast.  However, there are other ways to get a track close to the coast or get a landfall along the coast.  While this section scenario is a bit more difficult it can happen.  This will be explored with below graphic.  The below graphic is looking at the 500mb height anomalies from this morning's run of the GFS for Monday morning.  The blue shadings represent where a trough is positioned and the red shadings indicate where a ridge is positioned.  I have placed 5 numbers across features in which their evolution will play crucial to what happens with Jose's path:

1) This is the ridging which is building into the Gulf of Alaska and this is a feature of the negative PNA state.  This promotes a trough into the western United States and we see this with #2.

2) The result of that ridging building into the Gulf of Alaska helps to promote and shape a trough digging into the western-tier of the United States.  The result from this is to build ridging into the eastern United States and we see this with #3.

3) The result of the trough digging into the west is for ridging to build across the eastern United States.

4) A trough is positioned across Greenland and this is indicative of the negative phase of what is called the North Atlantic Oscillation (NAO).  Sandwiched between #3 and #4 is that strong ridging across the eastern United States.  This also creates what is called a "block".  This block is something that could prevent Jose from turning out to sea and the only possible track would be right into the east coast with a potential landfall anywhere from the Carolina's to the New England coast.

5) This is a cut-off low positioned right over the central Atlantic Ocean and the configuration with what was explained in #'s 3 and 4 further enhance this blocking.

If you look closely between the #4 and #5 notice the area of "white".  This could be a focal point as well.  This would represent a "weakness" or a gap inbetween that trough across Greenland and the cut-off low.  This could act as an escape route for Jose.  If that trough in #4 is not as strong as advertised or the cut-off in #5 is weaker or displaced further east, this opens the gates for a sharp turn out to sea.  If, however, that trough in #4 is stronger or that cut-off in #5 is stronger or further west we now have a higher probability for a track towards the coast with a landfall somewhere.  How these features evolve over the next several days will be extremely telling as to what scenario we can expect.

If we were to see any impacts here in southern New England what can we expect?  Depending on what happens with the overall track and intensity of Jose the possibility exists for some strong winds, either with the system itself or due to a rather strong pressure gradient which may develop.  The latest forecast from the NHC yields anywhere from a 20% to 30% likelihood of tropical storm force winds (sustained winds >= 39 mph) across southern New England with 30% to 40% probabilities just to the south and east of Nantucket.  This could certainly yield the potential for not only some wind damage but some power outages as well...especially since the trees are still fully leaved.  In fact, if we do see a scenario where we are looking at sustained winds greater than 40 mph we could see an enhanced likelihood for wind damage and power outages:

In addition to the potential of strong winds the potential would also exist for some heavy rains and flash flooding.  This, aspect, however, will also depend on exact track and overall strength.  What is a given though will be the high surf and swells along the coast.  Entering these waters is not recommended.  Coastal flooding will be very possible too, especially during high tide cycles.

Finally, even if we do get the worst of Jose but Jose is a weak tropical storm this does not mean we can't get torrential rains, some flash flooding, or strong winds.  In fact, tropical storms alone can produce just as much rainfall as hurricanes.  Some of our biggest flooding events have occurred with tropical storms or remnants of tropical storms.  This isn't saying we will see this scenario its just a way to make it understood that tropical storm conditions can still pack a punch.

Over the next few days the details should begin to become much more clear as to what track Jose will take and what type of impacts we will see from Jose.  Stay tuned!

What's the Deal with Hurricane Irma?

Much of the news story over the past few weeks has centered on the state of TX as Hurricane Harvey brought catastrophic flooding to much of southeastern TX, substantial damage thanks to intense winds and flooding, and also numerous tornadoes.  Not very far past Harvey, attention has shifted out towards the deep tropical Atlantic where yet another intense hurricane lies.  Hurricane Irma has blossomed into a dangerous category 3 hurricane and continues to strengthen as it makes a push towards Cuba and the Islands.

 If you follow social media or even some news outlets you may have encountered postings or have heard about computer forecast models striking the east coast with Irma or even perhaps a hit here in southern New England.  In my opinion, posting these graphics so far out is very irresponsible.  While of course a hit along the east coast is possible or even a hit here in southern New England is possible, we're talking about something which is 7+ days out.  While we can forecast in this timeframe with rather decent confidence at times, when it comes to tropical system the forecast confidence decreases drastically and there is pretty much no confidence at all.  In my mind, the goal for a forecaster, whether that forecaster be a degreed meteorologist or a hobbyist is to inform the public in a responsible manner, not scare the public.  The later is something that is easily done nowadays as social media has blossomed and this is because so much information gets posted and when this is done irresponsibility the wrong idea gets out.

While we are still several-plus days away from any potential landfall along the east coast there are numerous factors which will come into play which will determine; 1) If Irma makes landfall along the east coast and 2) where Irma would make landfall. Within this post we will look at all of those factors.

Over the past few days there has been rather strong agreement between the computer forecast ensembles have been in rather strong agreement in bringing Hurricane Irma very close to the east coast of the United States.  It is likely this reason alone which has led many to be discussing the possibility of a hit along the east coast.  Below are ensembles from both the GFS and European computer forecast models showing the cluster of potential tracks.  The GFS ensemble mean is from this morning's run of the GFS while the European ensemble mean is from last night's run (as of this writing this morning's run was not yet out):

While both computer forecast models show a great deal of members showing a landfall somewhere in the southeastern United States, the European model has several members which actually take Irma and curve it out to sea.  While a landfall somewhere along the east coast is possible, a re-curve out to sea is just as possible.  The million dollar question is; what determines whether Irma makes landfall or whether Irma re-curves out to sea?  This is where we explore everything that will play a factor in what the ultimate outcome will be.

Believe it or not, one of the key pieces to all of this is thousands, and thousands of miles away well out in the western Pacific Ocean in the form of Typhoon Sanvu.  Extensive research has shown that re-curving typhoons out in the western Pacific play a substantial role in the evolution of the synoptic weather pattern across the eastern central/eastern Pacific ocean and across North America.  More times that not, tropical systems are quite large in nature.  Within these systems a great deal of condensation occurs and the process of condensation releases what is called latent heat.  When you have these large systems with a great deal of condensation, you're going to get a great amount of latent heat release.  In fact, so much latent heat can be released that it actually shapes the weather pattern across the areas mentioned above.  This can be illustrated by looking at this mornings run of the GFS computer forecast model.  Looking at the jet stream at 250mb (almost 40,000' off the ground)) notice the extensive ridging (massive northward build in the jet stream) which develops across Alaska, western Canada, and the western United States over the next 5-days:

The significance of this ridging developing is it typically correlates with a trough (dip in the jet stream) either across the central and/or eastern United States.  Looking back at the image, notice the troughing develop and amplify (strengthen) between the central and eastern United States.  The significance of this feature is, when dealing with land-falling tropical systems across the east coast, and especially southern New England, this feature is nearly a prominent feature in many land-falls.  However, there is also more to this.  In order to increase the likelihood of a land-fall with this sort of scenario, you typically want the trough to amplify and become what is called negatively tilted as the tropical system is beginning to make the turn up the coast.  When this all occurs, the negative-tilt of the trough 'captures' the system and tugs it right into the east coast.  A great example of such a scenario would be with what occurred with Hurricane Sandy.

The next feature to focus on is across the northern Atlantic Ocean.  Again, using this morning's run of the GFS computer forecast model we will focus on the large area of high pressure which becomes established over a large portion of the north Atlantic:

  The importance of this feature is it could act as a block and actually prevent the tropical system from re-curving out to sea.  In this scenario, the only possible track would likely be into the United States.  Like with the troughing scenario, however, there is also more to this.  If the extent of this high pressure cell shifts eastward, this now opens up an 'escape' route for the system to make a re-curve out to sea.  How this high pressure center evolves over the next several days will be extremely critical in what Irma does as far as track is concerned.

The latest forecast track of Irma shows Irma potentially making striking Puerto Rico, the Dominican Republic, and Haiti regions:

  Not only would this yield substantial destruction across portions of these areas but the topography, especially of Haiti would drastically alter the strength and organization of the system.  When tropical systems go over land, they weaken significantly and rapidly as they need the ingestion of warm and moist air in order to keep going.  Also, Haiti is home to some rather large mountains.  If a tropical system goes over a mountain, if the mountain(s) are large enough, they can vastly disrupt the circulation of the tropical system which causes it to weaken substantially.

Some other factors to consider with regards to Irma are the degree of wind shear out ahead of Irma as well as available atmospheric moisture.  Tropical systems tend to strengthen when they reside in areas with weak wind shear and high amounts of available moisture content.  Assessing current wind shear across the Atlantic Ocean and just off the east coast of the United States we have low wind shear present around Irma and across the majority of the projected path of Irma.  However, across the eastern United States and just off the east coast we have rather strong wind shear:

The forecasts are for this region of stronger shear to remain in place for at least the next several days.  If this holds true, if Irma does take a turn towards the east coast or comes up the east coast, Irma could weaken quite a bit because of this.

Current water vapor imagery does show some drier air out ahead of Irma.  This may not be all that significant, however, if Irma does ingest some of this drier air this could act as a weakening factor for Irma:

 At this juncture its still extremely too early to say for certain what the likelihood is for a landfall across the eastern United States or if we have to worry about a landfall here in southern New England.  At this time, however, my best guess would be either a landfall off the southeast coast (perhaps SC/NC/N FL) or either a sharp re-curve out to sea once Irma nears the east coast.  However, the uncertainties are still rather high and any possibility remains on the table at this point.  All the latest data will continue to be reviewed and over the coming days we'll have a much better idea as to what solutions are more likely and which aren't.