Track Shifts Southward

Here's the 11 AM update from the National Hurricane Center:

showing that the anticipated landfall has shifted south into southern New Jersey / Delaware  However, and I can't stress this enough:  don't focus on where the center makes landfall.  Yes, a southward shift to the track means that we in the DC area will likely experience more effects from the hurricane.  High winds and rain will definitely be a problem.  But this storm is large.  And if the extratropical transition I mentioned a few posts ago happens, the effects of the storm will be felt over a very large area.

On the coast, the big concern is from the center northward.  It is there that the winds will be strongest, and the problem with tides and surf will be the greatest.

Right now, as you can see from the graphic above, Sandy has weakened considerably due to dry air intrusion.  This dry air has disrupted the circulation and caused the cyclone to be a minimal hurricane.  Forecast models suggest that the storm will reintensify once it moves north and passes over the warm waters of the Gulf Stream.

After that, the models suggest a lot of cold air will enter the cyclone's circulation which will start that process of tropical-to-extratropical transition.

Hurricane Sandy.  You can see the exposed center of circulation and the thickest clouds to the northwest.  This is caused by dry air surging into the hurricane's circulation.

A hurricane is a complex engine requiring precise circulatory patterns of air to sustain intensity.  Storms like this become so large, they create their own environments but larger-pattern flow can affect them.

 The graphic above shows the typical Northern Hemisphere hurricane circulation pattern.  The spiral rain bands bring warm surface air into the cyclone where it spins up into thunderstorms near the center of circulation and especially in the area right around the center called the "eyewall".

Air then descends within the eye back to the surface.

As you might remember from previous posts:  ascending air creates clouds and descending air dries out the atmosphere.  This is why the eye is clear.

Above the storm is the outflow sector.  Air that ascends in the storm must flow outward to complete the cycle.  If the outflow or the inflow is blocked, the storm cannot intensify.  If strong upper-level winds cut across this circulation and disturb the outflow, the hurricane can fall apart.  Check out this dramatic example of windshear tearing a hurricane apart:

 See how the low level circulation is exposed as the thickest clouds are blown away by the shear?  Some of this is happening to Sandy right now.   Because of the shear, it wouldn't be entirely surprising to see Sandy being downgraded to a Tropical Storm later tonight.

 Unfortunately, there's plenty of time left for the storm to strengthen again before landfall.

So...where are we?

For now, expect a southern New Jersey landfall sometime on Tuesday.  We should start seeing some initial effects here as early as Saturday night with some initial rain bands.  The winds will increase throughout the period and the rain/wind maximum should happen by Monday night into Tuesday.

What makes this storm so unusual and the reason for the hype surrounding it is the unusual path it is expected to take.  I can't remember nor can I find an example of a storm that "hooked" to the west and made a direct-hit landfall on this part of the country.  There have been plenty of "drive by" storms (Irene comes to mind) but this left turn to a due west heading may well be unprecedented.

It's not unusual to have this kind of flow pattern in the fall and winter.  Sometimes big winter storms get caught up in this type of flow and hover in an area for a couple of days.  In fact, with winter storms, we snow lovers hope for that type of situation.

But for a hurricane to be in the right place at the right time to be caught in that kind of flow?  Unprecedented.

And for a hurricane to be absorbed into another system instead of torn apart by it?  Well, I can only think of the Perfect Storm example.

While the entire region will be affected in some way, the coastal areas north of the center could experience conditions that haven't really been seen there before.

And in DC, we could see winds on Monday night and Tuesday sustained in the 40-60 mph range with higher gusts.  If the storm track is further south, look for that to shift to Sunday night / Monday.

Sandy Update: 11 PM

Latest update from the Hurricane Center continues the same forecast rationale but shows the turn in towards land happens a bit faster and, thus, landfall is further south - in central NJ.  That's not so great for us here in DC as it likely means more rain and wind probably starting on Sunday and lasting until Tuesday.

Sandy Threat: 5 PM Update

Here's the latest Hurricane Center update:

Not much change in the forecast rationale.  This update carries the storm through landfall in New Jersey.  The storm will be quite large (in areal extent) by landfall so the center isn't really a focus - this storm will effect the region from the Carolinas to the upper Northeast especially along the coast.

There are still some crucial details to sort out - and that should happen in the next couple of days.  Temperatures around here on Monday and Tuesday will struggle to get out of the 40's with wind and occasional heavy rain.  Snow is possible in the mountains.

All we can do is watch the models and see if anything changes but at this point, there's pretty good indications for a serious weather event in the Mid-Atlantic and Northeast early next week.

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.

South south south.

As you probably know by now given the forecast trends, the storm track has continued to shift south bringing less and less snow and less cold air to our region.

What looked like a bullseye 3 days ago has become another disappointment in this unusual winter.

I expect to see some snow later this afternoon and evening but certainly no important accumulations.

Guess we would have been better off asking the first model what was going to happen rather than depending on the GFS.

With the further-south track also comes less cold air so any precipitation will likely start as rain and change to snow.

The Return

Both of me, and possibly of SNOW!

I've been conspicuously absent from this blog since, well, August when Irene came along and flooded everything.  Actually, it was Lee that flooded everything but Irene didn't help.

In any case, there hasn't been much to blog about this winter - certainly no one wants to read a blog about the 1/2 inch of snow that's likely to fall on any given day.

But this weekend looks like the first (last?) real chance at a real snowstorm.  If it happens, and the models hold, it looks like we might be in the bullseye for this one which makes it fun, too.  At least it gives me something to write about.

Let's start where we always do:  the models.

Sorry.

The GFS at 57 hours (10 PM Saturday night) shows a pretty good storm organizing in the southeast US.  Note the blue line indicating the freezing point for this particular part of the atmosphere.  We want to be north of that line and at this hour, we're right on it.  That's a good thing.

Also a good thing?  That high pressure area in the Great Lakes that will be moving east and bringing cold air to our area which should make for fewer precipitation issues (snow vs. rain vs. sleet).

By 66 hours, the storm is really getting wound up.  It's phasing (or phased) with northern stream energy from the jet stream and is beginning the turn up the coast.  Notice that we're in the freezing zone by this point.  It's too early to tell how the precipitation will start, but if these model forecasts hold, the major portion of it should be snow.

At 75 hours, early afternoon on Sunday, the main event should be in full swing around here.  This shows moderate to heavy precipitation in our area and that we're well to the north of the freezing line.  The potential for significant accumulating snow exists.  But the storm track means everything and we're still more than 3 days from this model time.

At 78 hours, late afternoon Sunday, we're still in the thick of it.  The storm looks to slide off the coast, right along the freezing line so this likely means not much for our Northeast neighbors but a possible bullseye for us.

By Sunday night the storm is moving away, precipitation ends from west to east and our storm is done. 

Of course, the question is "how much?"

For now, I think the concentration should be on whether the models hold for another day.  If these runs don't change much and the other models fall into line, this looks like the real deal.  The ECMWF has been flip-flopping between a more southerly track and a more northerly track.  The southern solution means less precipitation for us so this all bears watching.

For now - the probability exists, I'd say better than 50%, for a significant snowstorm with 3+ inch accumulations starting late Saturday night and ending Sunday night. The possibility for more exists of course but this is the highest probability range for now.

Just for fun:  the GFS "clown" map:

which shows us just outside of the 4-6 inch range or so.  These aren't all that accurate this far out except to show the path and pattern of the snowfall.

Stay tuned. 

Here Comes Irene

I've decided to post a rare non-winter blog entry because of the impending hurricane here on the East Coast.  As usual, the post will be more concerned with effects in the DC area since that's where I live.

Irene is currently a Category 2 hurricane.  She has weakened a bit in the last day or so and has maximum sustained winds of 100 MPH placing it just inside Category 2 status (which begins at 96 MPH).  The intensity will likely not change significantly before landfall in extreme eastern North Carolina - probably in the vicinity of Cape Lookout tomorrow morning.

Two things to remember:

• This storm is large.  So is the extent of the rain and wind fields.  For this reason, its projected path offshore is still close enough to the coast to cause problems for us.
• However, the cut-off between significant rain and just a few showers is usually pretty sharp with hurricanes passing to our east.  If the storm follows the current forecast track, I'd guess that we'll get significant rain in the DC area - especially south and east of the city.

If this type of forecast sounds familiar it's because a hurricane's impact pattern is similar to the large snowstorms we get in the winter.  Track means a lot - although exactly where the center travels matters less...especially with a storm this large.  That's why the National Hurricane Center cautions people to concentrate less on the line that marks center track and just heed the warnings they issue.

Speaking of which...

We're under a Tropical Storm Warning here in the DC area - mostly for areas near water but including the following counties:

DISTRICT OF COLUMBIA...NORTHERN BALTIMORE...HARFORD...
MONTGOMERY...HOWARD...SOUTHERN BALTIMORE...PRINCE GEORGES...ANNE
ARUNDEL...CHARLES...CALVERT...PRINCE WILLIAM/MANASSAS/MANASSAS
PARK...FAIRFAX...ARLINGTON/FALLS CHURCH/ALEXANDRIA...STAFFORD...

SPOTSYLVANIA AND KING GEORGE.

And in St. Mary's county, the Tropical Storm Warning is now a Hurricane Warning.

So what should we expect?

The storm is likely to move fairly far off the coast so I expect the worst conditions on the Eastern Shore. 

Probably 6 inches of rain and winds gusting to 80+ there at times tomorrow.

Here, things start going downhill late tonight.  The first bands from Irene could arrive tomorrow morning

and the winds will be increasing all day.  Expect winds in the 20-30 MPH range by tomorrow afternoon,

increasing to 30-40 with higher gusts tomorrow night.  The worst should be tomorrow evening and 

overnight as the storm passes by to our east. 

Again, the cutoff for precipitation is expected to be fairly sharp.  I'd guess areas around I-95 could pick

up 1-3 inches of rain, more to the east, less to the west.  Places out in the Blue Ridge might just have a 

cloudy day.

This is a storm to take seriously but in DC, I also don't see the need to go out and buy all the bottled water

you can find.  Flooding is possible, power outages are probable and 50 MPH winds with saturated ground 

can make trees a problem.

The next official advisory from the National Hurricane Center comes out at 5 PM.

For now, here's an excellent graphic with the forecast storm track:

Boston Globe Irene Tracker