Tuesday, October 23, 2012

Sandy Likely To Threaten Mid Atlantic

The following is my own personal thoughts on Sandy and is provided as an advice article. I am not responsible for whatever actions you take in response to this article, and do not endorse or reject doing any activity directly in response to the following information.


I now believe Tropical Storm Sandy has real potential to affect the East Coast, whether it be from a tropical viewpoint or on the snowy side. This is indeed a pretty bold statement, so let's decipher why I think this could get serious.

The first thing we must examine is teleconnections. Above is a multi-model display of the 0z models and ensembles' predictions of the North Atlantic Oscillation. The North Atlantic Oscillation, or NAO, has two phases: positive and negative. In the negative phase, a colder and stormier pattern is encouraged over the East US as the jet stream dips south. In the positive phase, warm conditions can be found in the East.

Models are forecasting the NAO to stay well in negative territory, possibly well into November, but that's another story. The key piece is that the NAO will be extremely negative from now until October 27. Because teleconnections observations and their effects are delayed (the atmosphere doesn't work that fast), we want a good 3 day lag of negative NAO values before the storm strikes to show that the NAO would support such a possibility of an East Coast threat. Looking at the NAO forecasts, there is a good consensus on such a negative period through Halloween, which will enable the jet stream to dip in a negative NAO pattern. This provides a base for a theory on an East Coast threat.

The second item, potentially of much more importance, is something called the Fujiwhara Effect. The Fujiwhara Effect is named after Sakuhei Fujiwhara, and deals with interactions between two cyclones in close proximity. When I say 'cyclones', I mean a disturbance, tropical or non-tropical. The Fujiwhara Effect states that, when two cyclones are in close proximity, they will begin to orbit each other in a cyclonic flow (counterclockwise). To build off of this theory, let's look at the latest ECMWF forecast below.

This is the ECMWF forecast for hour 96, showing 850mb vorticity, 500mb heights, and MSLP readings. These three combine to give a fairly accurate depiction of where disturbances and high pressure systems are located. 96 hours (4 days) away from now, we see a very strong Sandy sneaking by Florida. However, notice the reds and oranges in the Ohio Valley and Northeast. That is a disturbance. We can now apply the Fujiwhara effect.

As the storm moves north (likely influenced by both the strong cyclone to the northeast and the advancing disturbance to the west), it has two options, which is the key player that is confusing the models. Here is a breakdown of each option.

Option 1: The storm moves north and is coaxed east by the strong disturbance located to the northeast in the image above. The storm keeps moving northeast and does not affect the US mainland.

Option 2: The storm moves north, but is more influenced by the disturbance in the Ohio Valley. The Fujiwhara Effect comes into play, and Sandy cycles to the west to orbit with the incoming disturbance over the Ohio Valley. This cycling persuades Sandy to move towards the US and make landfall.

If we look at the 12z ensembles forecasts for Sandy, we can see that they are showing both potential options happening. However, one can see that the edge is given to Option 2, where Sandy makes landfall on the Mid Atlantic/Northeast. Such a situation could be dangerous- similar to how Nor'easters 'bomb out' (rapidly strengthen) in the wintertime as they go up the East Coast, Sandy could very well do the same, bringing a tropical hurricane to an extratropical (not a hurricane) monster that would likely bring rain, snow, and a severe weather threat to much of the East US.

The ECMWF Ensembles (very reliable in my eyes) go as far as to say Sandy will merge with the Ohio Valley disturbance mentioned above and make landfall. Such a merge is called 'phasing', meaning two storms coming together into one. Again, the storms would be attracted to each other and Sandy would be persuaded to move west and retrograde (storms moving west in the North Hemisphere) into the US.

I honestly don't want to even discuss snowfall amounts, but here's some 'eye candy' for you winter weather lovers. This is off the 0z ECMWF and is 240 hour (10 day) snowfall total. This is from AccuWeather Pro and should be referenced as such if you are going to use this image. (Know that the data is not from Accuweather (snowfall forecast), the layout of the image is (color scheme, outline of image, etc.))

In summary: I believe that the East Coast has a threat on their hands. How great this threat actually is has yet to be determined. However, I advise all East Coast residents to keep a close eye on this system. If I lived in the Mid Atlantic, I might want to just keep an eye out at the moment, maybe make sure you have necessary supplies in the event of any evacuation at any time, not just for this event.



Anonymous said...

could we be looking at 9 inches of snow in philly

J. Clark said...

Good report Andrew! It is looking like the snow gods will be shining down upon central PA! I will be checking hourly for updates. Looking forward to this potential snowfall. Loving it!! Saltsburg, PA

Andrew said...

Anonymous: It's a bit too far out to know that much. I will know better probably on Friday.

J. Clark: Glad you liked it! There does indeed appear to be a snowfall threat if Sandy comes onshore.

J. Clark said...

If there is landfall with Sandy, I will be sure to post updates of current snowfall amounts in my neck of the woods. Saltsburg is about 35 miles east of Pittsburgh. I hope to see a snowflake or two anyways. Keep us posted Andrew. This is the best place to click for weather, period. Yay snow, sorry everyone had to say it again!

Janey said...

I hope this is right! I live in central PA and it's looking good if Sandy comes onshore! I just hope it is snow and not rain. Thanks for your weather reporting! I have added it to my favorites and check back quite often. Keep us posted with your thoughts of Sandys impact on Northeast please!!!

J. Clark said...

The European model in this post is very accurate. What Andrew has in this post is right on the money for snowfall amounts. Granted it is a 10:1 snow to water ratio, thus, depending on how cold it gets and if the snow stays at a 10:1 ratio for the duration of the weather event. For my area, Saltsburg, PA, when I added the amount it said that we would see between 18.4 and 27.8 inches of snow, precisely what the graphic in this post is saying. While this is possible you must keep in mind that the 10:1 ratio and duration of the storm will vary from the time the system begins until the end of the system. Therefore, using the ECMWF model, if everything goes 100% the way it is forecasting, then yes, indeed we will see some startling snow totals. However this is a long range forecast and there is still a great chance of seeing those numbers go down. I am thinking for my neighborhood, we could be seeing 2-8 inches, a far cry from 18-27, it all depends on how cold it gets and where and how far inland the system makes it. But, who knows, mother nature may have a trick up her sleeve!