Wednesday, October 24, 2012

Hurricane Sandy Staring Down East Coast

It should be noted that some information posted here is from yesterday's Sandy update. I repost it only because the information is still valid.

Tropical Storm Sandy has strengthened to a Category 1 hurricane as she moves a steady northbound track at this hour. Sandy has prompted hurricane warnings to be issued for much of the western Caribbean, with Florida also getting into the action. A tropical storm warning is in effect for the eastern coast of Florida, with a tropical storm watch surrounding that warning. With all the controversy swirling around Sandy, I still maintain my case that Sandy will pose a threat to the East Coast, and here's why:

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.

Shown above are the ECMWF Ensembles on top and the GFS Ensembles on the bottom. Both are from today's 12z model suite. As you can see, both indicate that a strong system will hit the Mid Atlantic in the days leading up to Halloween. The two ensemble sets are pretty similar in forecasts- both have a strong storm crashing into the Mid Atlantic, and this situation would indeed pull down very cold air as the GFS ensembles depict on the lower image.

I believe that an ensemble set always triumphs over a single model. Why? Well, imagine the ECMWF model. It's a great model, very reliable, a very good model overall. Now imagine that same ECMWF model, but now there's 52 of them, combined into one overall forecast. It sounds too good to be true, almost like a sure-fire forecast (for the record, that's nearly impossible, no matter the model). That sums up what the ECMWF ensemble system is. The same goes for how the GFS Ensemble system works.

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. Personally, at this point in time, I am favoring Option 2.

I've run over the model forecasts and weather theories to give my first (but certainly not last) forecast on Sandy. Keep in mind that she will be EXTRATROPICAL (not a hurricane, but a strong coastal storm like the ones seen in winter). However, this does not mean that the tornado threat will be nil- such a post-tropical cyclone can definitely produce some tornadic activity.

DISCLAIMER: These are my own personal thoughts and are subject to major change in the next several days.
DO NOT use this information in place of official government weather information.


Anonymous said...

will philadelphia get some snow action, and will philly see strong winds if shecome our way

wiiluigi1998 said...

I know there is no real answer, but do you have an idea if the storm will be a hurricane?

Andrew said...

Anonymous: They will see strong winds, but snow is kind of dicey.

wiiluigi1998: It already is a hurricane at this time, but will weaken and dissipate by the weekend.

ERN WX said...

WOW!!! This continues to look like the BIG ONE!!! People around here are kind of in shock. The ECMWF has done a great job. I expect the track will be a little further N though. The Apps and OH Val will get most of the snow. I will get washed out and blown away!!! No, I like strong winds. Any reports from this dangerous storm I will give. Thank you for providing great coverage of this storm. The lesson we all see, is -NAO=BIG East Coast storm.

Anonymous said...

what effect will this storm have on southern ontario snow/rain? high winds