By Meteorologist Sean Lowe
Today is the day where the national news media has caught on to the prospect of a nightmare of a storm affecting the northeast and/or Mid-Atlantic early next week (as well as creating halloween inspired names for it too). ZoomRadar has been following the latest model and National Hurricane Center forecasts for the past several days now. This update will go into some of the role players behind this unusual weather scenario.
First off, gotta love the the title of the 12Z HPC Long Range Forecast Discussion: “High Impact Merging of Energetic Systems Anticipated Off the Mid-Atlantic Coast.”
They of course are referencing the collision of an amplifying polar trough that is descending into the eastern US, with what is now Hurricane Sandy. The hybrid tropical system/Nor’easter that could result would be historical to say the least. Further implying the potential severity of the event, the NWS has ordered extra weather balloon launches (4x a day instead of the normal 2x) country-wide in order to feed the models with the most recent data.
Last night, Sandy impressed all those who are keeping an eye on her, as she became a strong category 2 hurricane, topping out with 110 mph winds before making landfall in Cuba. It has been fascinating to watch a late-October storm like this develop, let alone what happens from here…
Setting the Scene
From the very first model runs days ago that steered Sandy into the US mainland, most meteorologists knew that key synoptic (large-scale) features would need to develop with a certain strength and location in order for Sandy to simply be kicked out to sea. The North Atlantic Oscillation (NAO), is an index used to quantify 500mb height anomalies in the Northern Atlantic. Currently this index has tanked into the negative scale (in fact the lowest it’s been since June).
What is usually seen during this stage of the NAO is a blocking pattern that results in large east coast storms. I labeled the main features in this pattern using the 12Z GFS run 72 hours out:
Blocking high northeast of Nova Scotia and a strong ocean low out in the northern Atlantic.
The “spaghetti-maps” you might have seen online or on T.V. showed the vast uncertainty of model tracks. Most of the models are now catching on to these features and while nothing is set in stone 4-5 days out, the ensembles favor an east coast landfall anywhere from the mid-Atlantic to New England. Here are a couple of the “major” models:
12Z GFS Model, 132hr Sea-Level Pressure and 500mb height Forecast:
-Landfall occuring in southern New England.
12Z European Model, 96hr Sea-Level Pressure and 500mb height Forecast:
The Weather Service 5-day forecast map has a scenario similar to the GFS.
The NWS places the cold front nearing the coast Monday morning. The cold airmass to follow will be ingested by Sandy and will contribute to the “bombing-out” of the low pressure. This rapid decrease in pressure often occurs between a polar airmass and much warmer tropical air (October/November is a GREAT time for this to happen). While I think a sub-950mb low might be overdone by the models, the pressure gradient is sure to look impressive.
As the system loses its tropical characteristics, the wind field will spread out rather than remaining confined to the center. Sustained winds could range from 50-60 mph with hurricane force gusts.
The low is bound to slow down as it makes landfall and with all the tropical moisture still associated with with it, prolonged rain events could result in major flooding.
Here is the NOGAPS 6hr forecast of rainfall totals around the time of landfall:
(to be used loosely, but nonetheless puts the amount of moisture associated with Sandy in perspective)
Another major issue of a storm with such a large diameter, is the ability for the seas to be driven up immensely. Especially when tropical storm force winds are forecast to extend 250+ miles outwards from the center.
On top of a mid-900mb low churning up the waters, the lunar cycle will be in favor of high wave action along the coast.
The phases I boxed in red are inconveniently set to occur at the onset of Sandy. A spring tide occurs just after the full moon and gravitational pull on the water will be strongest.
Yes, the backside of the storm could eventually pull in enough cold air down from Canada to cause snow in higher elevations perhaps in the mountains of say, West Virginia. TBD where and when this could happen…
In wrapping things up, here’s a neat graphic showing the latest reconnaissance flight which shows the incredibly large wind field on the east side of the storm:
Be prepared but not panicked. Let’s get a better picture of where the storm is heading in the next few days.
Interestingly enough, Halloween was pretty much rescheduled in my town of Bedford, NY last year due to the early season snowfall that occurred while leaves were still on trees bringing power lines down everywhere. Not hoping for a repeat…