Sandy Trouble for the Mid-Atlantic / Northeast?

Hi everyone!  I guess we're starting a bit early this year.

For the record:  I expect this winter to be significantly snowier than last winter - so, if that ends up being the case, there will be lots to blog about.

First, though, there's Sandy.

In 1991, right around this time in fact, an intense low pressure system developed off the coast of Canada and moved southward because of a large blocking high pressure system.  The storm became so large and organized that it actually absorbed a hurricane (Grace) and became a hurricane itself.  The Perfect Storm, as it would be known, eventually impacted the Mid-Atlantic and Northeast - largely through huge surf and the resulting coastal damage.  If the storm had actually made landfall, it would have been much much worse.

Satellite image of The Perfect Storm on the morning of November 1, 1991.  The hurricane has already formed in the center of the circulation although NOAA elected to leave it unnamed to prevent confusion.

While this is not the same situation, we have another case where a large system (in this case, a strong cold front moving across the country) could significantly affect the track of a hurricane (in this case, Sandy).  And this time, it looks like the effects on the east coast could be more direct - especially if certain model solutions verify.

Weather forecasts are fraught with conditional language.  "Could", "if", "might", "chance" are the vernacular of most meteorologists and the reason - as I've often mentioned - is that the atmosphere is a hugely complex system where any small change in a particular parameter could change everything about a forecast.


That said, it seems likely Sandy will continue to move north or north-northeastward for the next 36 hours or so before curving somewhat more to the northeast.  At that point, several factors will combine and how they combine is really important.

Most models now forecast Sandy's northeastward motion to accelerate on Saturday and Sunday.  If the timing of the incoming cold front is just right, sometime on Sunday the accompanying trough may "capture" Sandy and that's where the problems really begin.

A couple of days ago, this "capturing" looked unlikely to happen.  Now the timing and system locations look more and more like it will happen.  In fact, only one model right now suggests that the storm will pass harmlessly out to sea - i.e. that the trough will miss the capture and Sandy will become what is referred to as a Fish Storm.  And actually, looking at the latest model runs, I think that one has jumped on board as well.

The official National Hurricane Center forecast (at 11 AM 10/25) shows the capture taking place on Sunday and the storm turning in towards land by Monday with potential landfall on Tuesday as an extratropical storm or hybrid.

At the same time, colder ocean surface temperatures and interaction with the trough will probably cause Sandy to begin transition to an extratropical cyclone.  In technical terms, Sandy will be changing from a warm-core low (tropical system) to a cold-core low (extratropical).  In practical terms, the winds at the center of circulation will begin to weaken but the wind field itself would spread out significantly from the center meaning that places well inland could have tropical storm-force winds.

We could be looking at practically every weather effect you can think of from a storm like this.  There would be big problems with surf, coastal beach erosion and wind damage at the coast - especially at and north of the center landfall location.  Winds of 70-80 miles per hour at the coast would be common - even in places like New York City and especially in Long Island and points to the north.  Rainfall amounts will vary by location and I'm not sure at this point how much we'll see here but areas in the northeast will likely receive many inches of rain and elevated areas - especially in Pennsylvania and New York - could see a lot of heavy, wet snow.  Tropical storm-force winds could affect the entire region which means a lot of tree damage.

Here is one of the latest model runs showing the storm position on Halloween just off of New York City:

If this verifies, this would be a historic storm - the type that gets named afterwards (and I don't mean something like "Sandy"). 

In some models, the storm actually does a loop before heading out to sea.  During this loop is when we in the DC area stand the best chance of receiving precipitation although I think that we would see winds and clouds before then.

The time frame for effects here looks to be starting on Sunday and lasting into Tuesday night with wind and clouds initially, some rain during the curve into the coast and then, depending on what it does next, some lingering effects.

There is a lot of uncertainty as to the particulars of who-sees-what.  Right now, what seems least likely is that Sandy will go harmlessly out to sea (unfortunately).  Readers in the northeast and along the coast should consider making preparations soon and we'll watch this for the next couple of days to see what its going to do.

Snow is fun and big storms in the winter are fun but there's nothing fun about this one.  This could be really bad - especially north of the DC area along the coast.  Let's hope something changes in the next 48 hours to take Sandy out to sea.

More to come.