Remembering Sandy – 1 Year Later

Damage from Sandy in Fairfield

We dodged a bullet with Sandy. Yes, that’s right – we lucked out. While people who lost homes and businesses during the storm would likely disagree with that assessment (and for good reason) the damage from Sandy could have been exponentially worse.

Stamford Hurricane Barrier (Courtesy: Army Corps of Engineers). Green - astronomical tide, Blue - observed water level, Pink - surge/residual.

Stamford Hurricane Barrier (Courtesy: Army Corps of Engineers). Green – astronomical tide, Blue – observed water level, Pink – surge/residual.

The peak wind and storm surge during Sandy struck near low tide. Had Sandy arrived 4 hours later the storm surge would have been record breaking and catastrophic. The images from the New Jersey shoreline would have been displaced 100 miles north on the Connecticut shoreline.

Sandy in Connecticut was also an example of how storm preparedness and good communication can work. Local media, towns, and the state seemed to all be on the same page with storm impacts and the appropriate response. By and large evacuations were successful, utilities responded quickly to outages, people took the necessary steps to protect themselves and their families. Granted, a lot of this occurred because of Tropical Storm Irene a year prior, but it was nonetheless an impressive and successful preparation and response to Sandy here in Connecticut.

More on Sandy: Storm Summary / More on Sandy’s Wind Damage

 

Advertisements

A Closer Look at Sandy’s Damaging Wind

We’ve spent a lot of time talking about Sandy’s storm surge but the wind associated with Sandy along the Connecticut shoreline was quite impressive. In fact, the recorded wind gusts were some of the more impressive wind gusts I’ve ever seen at the official ASOS stations on the coast here in Connecticut.

When factoring in the duration (i.e. not a quick hitting thunderstorm) and how widespread the 60 knot gusts were (i.e. not in just one corner of the shoreline) this is probably the strongest wind storm on the Connecticut coast since Hurricane Gloria in 1985.

The peak gust of 66 knots at BDR was recorded at 21:03 UTC and the lowest pressure was recorded at 22:02 UTC with 971.9 mb. This graph of wind and pressure is what you’d expect for a hurricane passing near (but not over) a certain area. Hurricanes have a tight radius of strong winds near the center of the storm with lower wind velocities the farther one goes from the storm’s center. While Sandy was a hybrid storm it did maintain an inner core through landfall that contained the strongest winds.

If you look at the RUC proximity soundings around the time of lowest pressure at BDR you can see some interesting things. I’ve attached the BUFKIT soundings from the surface through 800mb at Sikorsky Airport at 18z, 21z, and 00z. Note the time listed is standard time and not daylight saving time.

The top sounding form 00z shows a very shallow mixed boundary layer. The mixing depth is only around 700 feet with a wind velocity of 59 knots at 700 ft AGL. Not surprisingly, the hourly gust at BDR was 46 knots.

By 21z the mixing depth was similar but the wind field was a bit stronger. At 21z maximum wind gust was 49 knots but by 21:03 UTC a peak gust of 66 knots was recorded! While the RUC sounding only shows a 64 knot wind at the top of the shallow mixed layer by 22 UTC (not shown) the wind at that level increased to 74 knots. It’s possible the RUC analysis missed the northern extent of the stronger wind field at 21 UTC. In addition, the boundary layer was in the process of drying out and warming up. Between 20:52 UTC and 21:42 UTC the temperature spiked from 16ºC to 18ºC which means the mixing depth may have been a bit deeper than 700 feet.

By 00 UTC, there’s no question the mixed layer is deeper up to 1900 ft AGL with 77 knot winds there. Impressive. Below is the first SPECI with the 66 knot gust. There were also several 63 knot wind gusts at BDR at 22:01 UTC, 22:31 UTC, and 23:19 UTC.

SPECI KBDR 292142Z 08044G56KT 2SM -RA BR SCT014 BKN025 OVC030 18/16 A2873 RMK AO2 PK WND 06066/2103 P0001

The 00z OKX sounding shows the same thing with a raging jet just off the deck and a mixed boundary layer into a portion of that stronger jet (69 knots at 445m AGL).

As mentioned in my Sandy summary blog post we’re lucky that the soil was dry and the trees were mainly bare. Had winds like this occurred a month earlier the wind damage to trees would have been exceptionally more impressive than what we saw.

After the wind died down Tuesday  morning Connecticut Light and Power had just shy of 500,000 customers without power. Not surprisingly, the highest number of outages were along the shoreline and in the more rural parts of Connecticut. Areas with elevation in the northwest and northeast hills saw somewhat higher winds than the Connecticut River valley.

These outages would put Sandy on par with Gloria for number of outages and behind Irene and the October snowstorm (which holds the record of 803,000).

There’s no question this storm produced an impressive and powerful several hour burst of damaging wind shortly after nightfall across the state. Getting several hours of 60+ knot wind gusts at various reporting sites in the state is impressive. I can’t recall a storm since Gloria being able to do it here in the state.

Dangerous Sandy Eyeing the Northeast

Hurricane Sandy / Courtesy: WeatherTap

The northeast is facing a serious threat from Hurricane Sandy with the potential for a devastating impact somewhere in the storm’s path. The exact track is still uncertain as we are about 96 hours out before the brunt of Sandy will approach.

Hurricane preparations should begin for people living in Connecticut tonight or tomorrow. You will have Friday, Saturday and most of Sunday to prepare. Threats include serious coastal flooding, inland flooding, wind damage, and prolonged power outages. The extent of any of these threats is too early to know but it’s important to be prepared for any event.

I do think, however, that this storm will be an historic event for someone in the northeast. Too early to say if it’s New England or Washington, D.C.

This is the 5 p.m. forecast from the hurricane center. The forecast shows Sandy jogging east of North Carolina (over the Gulf Stream, by the way) and then hooking left toward the northeast. This type of track is virtually unprecedented for a New England hurricane (accurate records back into 1800s) yet is forecast by virtually every tool at our disposal.

The NHC keeps the storm a hurricane up until landfall and then transitions it to a “post-tropical” low that still contains powerful 65 mph sustained winds (which is what Irene was at landfall in New York).

Our computer models are in remarkable agreement with a track that takes the storm into New England or the northern Mid Atlantic. There are a few outliers, such as the 12z op Euro, that bring the hurricane into the southern Delmarva penninsula but that seems unlikely to me. It would be extremely difficult to get a hurricane to take such a hard left hook to start moving due west of event south of west like the Euro shows.

While the vast majority of these tracks would produce a signifcant impact in Connecticut the exact track may mean the difference between a full fledged hurricane and what would seem similar to a more typical fall-like nor’easter.

The question becomes what will the intensity of Sandy be at landfall and will she still be a hurricane? The answer to the second question is, in my opinion, yes. As I discussed yesterday the models keep Sandy as a warm core system during its slow extratropical transition. That continues today per Bob Hart’s cyclone phase space diagrams.

With Sandy expected to maintain a warm core and feature an expanding wind field the concern for serious impacts is quite high. Our computer models indicate that the hurricane may actually strengthen as it approaches the northeast. With colder waters to our south how is that possible? The answer is that the models show a remarkable amount of synoptic scale lift that will make strengthening of the storm possible as it heads to our latitude.

We always talk about the jet stream and how it influences our weather. Local maxima in the jet stream, called jet streaks, are what lead to really fun kinds of weather.

From quasigeostrophic theory it’s easy to come figure out which areas of a jet streak feature rising air or sinking air. It can be done with PV thinking too (which I actually think is a cooler way of demonstrating) but here’s the deal with QG.

Jet Streak Schematic / Courtesy NC State

108 Hour GFS 250mb height/isotach Forecast

In a jet streak you have rising motion in the right entrance region and left exit regions. In Sandy’s case you can see 2 powerful jet streaks in the eastern U.S. There’s also a smaller (easterly) jet streak over Newfoundland and a second jet out over the north Atlantic southeast of Nova Scotia.

I labeled the favored areas of the jet stream for QG upward motion with LFQ for left front (exit) quad and RRQ for rear right (entrance) quad. I’ve never seen a coupled jet structure like this in my life over this part of the Atlantic. The “Boom!” indicates what will happen in between the 4. Even if there wasn’t a hurricane coming north we would probably still see a sizable nor’easter given this setup near the tropopause.

All of this results in an extremely large area of upper level divergence that will be located over Sandy. This divergence will help keep the storm intense and possibly, depending on how the Sandy’s extratropical transition goes, intensify the hurricane.

All of this means we need to be prepared for a direct hit from a hurricane. While it’s certainly possible that this storm will just miss us to the east or west the wind, rain, and coastal flooding from Sandy will stretch far from the actual landfall location. It looks like Sandy will be quite a storm for someone… let’s hope it’s not here!

 

Some Impact From Sandy Appears More Likely

Our computer models are slowly getting into better agreement that hurricane Sandy will pay someone in the northeast a visit by early next week. The threat area for a direct hit stretches from North Carolina all the way to Nova Scotia.

12Z Euro 500 mb Heights/Vorticity 84 Hour Forecast

The giant “block” that we’ve been talking about over the Atlantic Ocean appears strong enough to prevent the hurricane from sliding east and out to sea.

The block itself is what’s called a Rex block. Rex blocks occur when a ridge of high pressure exists poleward of a cut-off low pressure. These patterns are somewhat stable and slow to change. To the west of the Rex block a ridge of high pressure (red dashed line) is nosing up from the Caribbean to the north Atlantic. This ridge is effectively preventing Sandy from losing too much longitude as it heads to the north.

So will the block hold? There was some hope  that a weakness would develop allowing Sandy to sneak out to sea. It does not look like that will happen with only a handful of pieces of available guidance (including the 18z operational GFS and some of its ensemble members) showing an out to sea track.

Here’s a spaghetti plot showing all the different GFS ensemble forecasts. Basically, each line represents a separate forecast using initial conditions that have been tweaked a bit to represent the inherent uncertainty in our ability to capture an accurate initialization of the atmosphere.

12z GEFS Ensemble Members

You can see here that even the ensemble members that appear to have found an escape route near Bermuda get stuck in their tracks and are forced to turn around by the block. This tells me, when coupled with the Euro ensembles and most other computer models, that a trip out into the open Atlantic is unlikely. It’s a fairly good bet (better than 50/50 chance) that this thing is coming toward the U.S.

But just how close it gets to Connecticut is an open question. It’s also unclear when the storm will make landfall. Some computer models bring Sandy ashore Sunday night. Others bring it ashore Tuesday night. Some models target Maine for a direct hit while others like Ocean City, Maryland. There are several that have a bullseye right on Connecticut and Long Island.

Until we have a better idea where the storm will make landfall it’s impossible to get too specific with the exact hazards and threats that Sandy will pose. We are still 5 days from a possible impact which is an eternity when forecasting a hurricane’s track!

It’s also unclear how strong the storm will be when it reaches the northeast.

There’s no question the storm will be “warm core” in nature by the time it reaches our latitude. It will not be an extra-tropical storm. This means the storm’s strength will decrease with height the way hurricanes do! It’s also likely that Sandy will develop frontal systems (or baroclinicity) which is a trait of an extra-tropical storm. Basically, the storm will be a hybrid between a nor’easter and a hurricane.

It’s important to note that a warm-core “hybrid” can be quite dangerous and powerful. The hurricane of 1938 (This is an example folks…. not comparing the two!!!) was likely a hybrid storm as was the 1991 “Perfect Storm”.

Here’s a way to quantify the storm’s forecast hybrid characteristics courtesy of Bob Hart of Florida State University. This cyclone phase-space shows how warm core a storm is (i.e. how a cyclones’s intensity varies with height) and how symmetric a storm’s temperature gradient is. A purely tropical system would have an intensity decreasing with height (can measure this from the thermal wind) and no temperature gradient tangential to its motion.

This indicates the potential (based on 12z GFS) for Sandy to strengthen once it undergoes extratropical transition. It appears as if the storm will become a dangerous warm seclusion. This means it will have an asymmetric thermal gradient yet remain warm core. Warm seclusions are infrequent in our neck of the woods and they’re characterized by a large radius of gale force winds and a tight (tropical-like) core of stronger winds near the storm center.

For what it’s worth the cyclone-phase space indicates that this will be a deep warm core system (can figure this out by comparing the thermal wind in the upper troposphere to lower troposphere) and not a more typical shallow warm core system.

While the pressure readings I’ve seen from some of the global models look far too low (i.e. 930ish mb) there is the potential for this storm to be quite intense. When coupled with an astronomically high tide the concern is there for coastal flooding for anyone in the storm’s path. Wind damage and heavy rain will also be an issue somewhere near Sandy’s path. Will that be here in Connecticut? It’s just too soon to tell.

We’ll have to watch Sandy closely over the next few days but at this point I’m becoming increasingly concerned about a rather serious storm somewhere in New England. There remains an outside chance that this storm could smack Long Island and southern New England directly as a hurricane. There’s also a chance, albeit a small that, that the storm is able to sneak through a weakness in the block and head out to sea like the 18z GFS and some of its ensembles now show.

Even without a direct impact coastal flooding and flooding rains are possible with a storm thats hundreds of miles away as a secondary low pressure system may develop off the coast and absorb some of Sandy’s moisture. We need to keep our guard up and be ready to start preparations when Sandy’s probable path and strength becomes more clear. This is a low confidence but potentially very high impact storm.

Sandy… Please Start Your Jog East!

When you see an exceptional weather model run or two on a day 7 or 8 forecast you expect it to go away. Every once in a while we see a bit of long range weather porn pop up on the computer models only to quickly disappear.

12z GFS Ensemble Forecast / Courtesy: Weather Underground

Sandy is a bit of a pain, however. She’s not behaving like most tropical storms or hurricanes do. The “spaghetti plot” of this afternoon’s GFS ensembles really tells the story with 2 distinct possible paths for Sandy.

This is one of the oddest spaghetti plot I’ve ever seen for a storm threatening the northeastern U.S.! While half of the GFS ensemble members curve the storm east (including the operational GFS in white which is in the out to sea track)  the other half of the models take Sandy to just east of Cape Hatteras and sling shot it west into New England. That would be one of the most unusual paths ever documented for a New England tropical storm or hurricane!

The operation European model agrees with the left hook bringing Sandy ashore in southern New England as a hurricane from the southwest. Exceptionally unusual.

12z Euro QPF/MSLP / Courtesy: WSI

There is no doubt in my mind that the European model is overdoing the strength of this storm. It has a tendency to strengthen storms like this that are undergoing extratropical transition a bit too much. Needless to say a track like this is concerning.

So what should we make of it all? At this point we are still at least 36 or 48 hours from really getting a good handle on Sandy. The reason for all these funky looking computer model solutions is that the weather pattern is very amplified and all blocked up!

Euro Ensemble Mean 500mb Heights (156 hour forecast) / Courtesy: WSI

The Euro Ensemble mean shows a monstrous ridge over Newfoundland and Greenland which may act as a block for Sandy and prevent it from moving out to sea. The positive height anomalies near Newfoundland are nearly 4 standard deviations above normal! The large rex block that develops in the next 72 hours will transition to a large omega block which is pictured above (the height contours make on outline of the Greek letter omega). How this block evolves will determine whether Sandy can escape to the east like the GFS shows or get shoved up the coast like the Euro shows.

Hurricane Esther Best Track / Courtesy: Unisys

While we have seen truly anomalous New England hurricane tracks in the past – they are few and far between. Here’s a look at Esther from 1961. What the heck was Esther doing out there???

The category 4 hurricane approached New England from the south and then the storm did a loop south of Cape Cod. The storm made 2 landfalls in New England.

Other storms have done odd things. Most notably, the Great New England Hurricane of 1938 which was in the process of being absorbed by a large cut-off low that was diving south of the Great Lakes.

1938 Hurricane Best Track / Courtesy: Unisys

This hurricane tracked due north or maybe even a hair west of due north and then hooked left south of Montreal toward Toronto.

The fact that we need to look back to 1961 or 1938 to find hurricanes that impacted New England that took really unusual paths says something about just how hard it is to get a storm to get absorbed at just the right time by the jet stream and hook left into the region and not head out to sea or continue due north.

Even if Sandy takes a path that will indirectly or directly impact us it’s not clear how strong the storm will be. While there is a very outside chance of a direct hurricane hit the more likely scenario is a brush or a hit with a hybrid system that will act like a fall-nor’easter that is spinning around in the north Atlantic.

No need to panic! Let’s watch things and see how they shake out over the next day or two. My gut feeling is that the computer models will trend away from the extreme solutions (they almost always do) and we’re left with something in the middle.