Hurricane Joaquin discussion

The prolonged stretch of dry and tranquil weather here across southern New England is about to come to an abrupt end as we enter the first week of October.  As we move towards the later half of the week and towards the weekend, our attention is strictly focused on what is now Hurricane Joaquin which is located just northeast of the Bahamas.  Several pieces of computer forecast guidance, including ensemble members all indicate that Hurricane Joaquin will make landfall somewhere along the east coast, with perhaps anywhere from VA to NJ receiving the highest likelihood of a direct hit.

The latest (2:00 PM EDT on September 30th, 2015) advisory from the National Hurricane Center (NHC) has Hurricane Joaquin as a category 1 hurricane with maximum sustained winds of 85 mph near the center and with hurricane force winds extending outward up to 35 miles from the center with tropical storm force winds extending outward up to 125 miles from the center.  The estimated central pressure is 968mb.  The NHC is also forecasting further strengthening of Joaquin over the next couple of days and aren't ruling out the possibility of Joaquin becoming a major hurricane (sustained winds of at least 115 mph).  Below is the latest forecasted track:



Notice the large shape of the cone in the projected track.  This cone is referred to as the "cone of uncertainty".  The larger the spread within the cone, the lower the confidence in the exact track of the storm.  The reasoning behind such a large spread is due to the fact that the atmosphere will be undergoing some incredibly complex changes over the next several days and how the pattern exactly evolves is going to vastly influence what happens with Joaquin's track.  We will explore this further below and get into the reasoning as to why the pattern will become so complex and why our computer forecast models are/will continue having a very difficult time.

One reason for the large spread in track is purely due to the large spread with computer forecast model ensembles.  Below is a graph composing of various computer forecast models and their mean projected track.  This chart is called a spaghetti chart because...well all the different tracks and such resemble a piece of cooked spaghetti.
 

Notice you have a cluster of models bringing Hurricane Joaquin into VA/NC , then another small cluster up around northern VA/MD and then a few tracks into portions of southern New England and even a couple straight out to sea.  From this we can gather a couple pieces of information:

1)  There is much spread within the models which means there is a very low confidence at this time as to exactly where the storm will track and where the storm will make landfall.  When these plots and lines are much closer together, this is when confidence is typically much higher.

2)  It does appear there is a stronger cluster of the data out across the mid-Atlantic coast (NC/VA/MA) area.  What we can decipher from this is that perhaps the likelihood of a landfall anywhere in this area may be more likely.  However, given the spread as mentioned above, we can't say this with the highest of confidence.

When it comes to the forecasting aspect, as mentioned a bit earlier, the atmospheric pattern configuration is going to be quite complex with many variables all tying into how the system evolves and where it tracks.  Depending on how each feature (which we will discuss below) evolves, that will impact what happens with the system.  We will take a look at some of the important features below which are labeled on the map:
 

 The above graphic is from one of our computer forecast models, the GFS and this is from the 12z run (8:00 AM EDT) from this morning projected out to 48-hours.  So we're looking at 8:00 AM EDT Friday morning.  This particular graphic was just chosen to provide a visual of the key features at play.

1) Trough - This trough will be a major focal point over these next several days.  Computer forecast models really amplify the trough as it moves into the southeast and digs it very far south.  The trough is also expected to become negatively tilted.  What computer forecast models do is as Hurricane Joaquin begins to turn more to the north and west, the trough will eventually capture Joaquin and bring the system right towards the East coast.  So the question here becomes, if/where this capture takes place.  If it takes places further south and earlier, the chances vastly increase for a landfall perhaps across VA/MA area.  If it's later and slower with the capture, then the chances for a landfall further north increase.

#2, #3, and #4 - I grouped all these together because they are will seemingly work in conjunction with one another...well at least with respect to what happens with Joaquin.  The strong high pressure to our north, and ridging off to our east will ultimately do its very best to keep Joaquin closer to the coast.  That cut-off low (#4) will also work to prevent the ridging (#3) from sliding east as well which would allow the opportunity for the Hurricane to slide east.

So with all this...what can we perhaps expect here in southern New England?  At this juncture it appears that the highest likelihood for the most significant impacts will be somewhere along the mid-Atlantic coast where substantial impacts may be possible.  Up here across southern New England we may get spared, however, we could still deal with the potential for a quite a bit of rain, some wind and maybe some flooding.

Confidence should continue to build over the next few days as hopefully our computer forecast models develop a better consensus.