Ramblings of Meteorologist Jim Sullivan

This post will be divided into four sections, so you can scroll down to what you’d like to read about.

-Sandy: Current and short term forecast

-Model madness: Trying to pin down the track of Sandy into the Northeast US

-Meteorological Insanity: Trying to figure out how strong Sandy will be as it hits the Northeast US

-Be Prepared: Preliminary Impact Graphics

Sandy: Current and short term forecast:

Above is a current look at hurricane Sandy, as of 12:45pm EDT on this Friday. As has been expected, shear and dry air associated with an upper level trough of low pressure have caused Sandy to expand and begin taking on sub-tropical characteristics. Sandy is still a powerful cyclone with sustained winds of 80MPH over the northern Bahamas and a minimum central pressure of 970mb as it slowly moves north.

As Sandy pulls north of the Bahamas it is expected to maintain minimal hurricane intensity due to a large area of upper level divergence near the cyclone. The wind field of Sandy, as can be seen on the satellite image above, is expanding, and will continue to slowly expand as Sandy becomes more and more non-tropical on its way up the east coast. Due to the large nature of the wind field, even though Sandy is expected to track well off-shore of the Carolinas, tropical storm force winds will be possible, especially in areas close to the coastline.

When looking at the GFS model forecast for Saturday morning, what stands out is although strong upper level winds will continue to pierce through the center of Sandy off the southeast US coast, the very strong upper level winds appear to be “fanning out” north of the hurricane. This will allow for significant lift to occur with Sandy through the weekend and allow the storm to maintain a low pressure and category 1 hurricane intensity this weekend, even if the system doesn’t look like a classic hurricane anymore.

Model madness: Trying to pin down the track of Sandy into the Northeast US

Above is a look at this afternoon’s GFS (American) and European model runs. This afternoon’s GFS took Sandy farther north; towards the Long Island area this run of the model while the European model took Sandy farther north than it has, however is still farther south than the GFS into NJ. When looking at the two models above valid Sunday morning, the differences are very subtle:

1. The two models are in remarkable agreement in the Pacific and western N. America pattern.
2. The two models are almost identical in the north Atlantic, with one exception: The GFS is still a little bit weaker with the strip of ridging between Sandy and the ocean low to the east. This allows Sandy to swing a little bit farther east on the GFS before phasing with the incoming trough, resulting in a landfall a bit farther north than the Euro.

Other than small disagreements in how far east Sandy can swing out before being captured by the incoming trough, the two models both appear to handle the phase of Sandy and the incoming trough well…with both models showing a little bit of Fujiwhara interaction between the two features before Sandy accepts its fate in merges with the trough.

In general, the GFS and last night’s European ensembles agree on this type of scenario…with the GFS ensembles clustering on a NJ to Long Island landfall and last night’s European ensembles keying on a southern NJ landfall.

Given this general agreement, I still expect Sandy to landfall in NJ Monday night or Tuesday morning, with some risk of a landfall farther north or south:

Risks to this landfall forecast:

1. If the incoming trough ends up stronger or weaker than expected, phasing may occur sooner or later than currently expected. This would result in an adjustment in this track forecast.
2. If the Atlantic ridging is weaker or stronger than expected, Sandy may swing more or less out to the east before hooking back towards the NW, resulting in a landfall farther north or south.

Meteorological Insanity: Trying to figure out how strong Sandy will be as it hits the Northeast US

Above is a look at meteorological insanity—a hybrid, very strong low pressure system pegged under a very deep upper level low hitting the east coast of the US—as projected by the European model. The media has tossed around terms like “Frankenstorm” and “Perfect Storm II” to describe this storm as it moves ashore. Will it be all that it’s hyped to be as it moves in?

To answer that question, let’s look at the forces that will help strengthen or weaken Sandy into early next week. A look at the current upper level plot shows that strong upper level winds are causing considerable shear over Sandy, which is located just north of the western Bahamas at the time of this image. However, one can see that as mentioned earlier, the upper level winds north of the center are fanning out, which is creating upper level divergence or lift, shown by the purple. This will help Sandy maintain its deep central pressure—currently at 970mb—and aid in convective development, when combined with the warm waters of the Gulf Stream:

These two factors support Sandy remaining a deep cyclone through the weekend as it tracks off the southeast US coast. The strong upper level winds however will continue to shear Sandy, meaning it will remain a sub-tropical cyclone, and also meaning any intensification over the weekend will be minimal. Essentially, I am expecting Sandy to maintain category 1 hurricane intensity with a pressure around 970mb through the weekend.

As the trough currently over the upper Midwest continues to amplify, an extremely impressive jet structure will set up over the eastern US and western Atlantic. The above image off the GFS model, valid for Sunday evening, shows three jet streaks providing for mass evacuation of air over Sandy (due east of North Carolina at this point). This will provide for tremendous lift and should allow for Sandy to begin deepening more at this point.

Once Sandy phases with the upper level trough on Monday, significant mid-level height falls will ensure over the storm. Note how on this image, from the GFS valid early Tuesday morning, the mid-level heights, represented by the black lines, are much lower along the Mid Atlantic coastline than over surrounding areas. This occurs when the lower heights with the trough combine with the lower heights of Sandy, resulting in a very deep mid-upper level low pressure system over Sandy. This, combined with significant mid to upper level spin in the atmosphere, indicated by the color-fill, will result in tremendous low to mid-level lift with Sandy, which will aid in the system further lowering its minimum central pressure Monday as it nears the northeastern US.

In addition, once the warm, remaining tropical core of Sandy gets caught under the cold core trough aloft, it will aid in providing for lift over Sandy due to the buoyant nature of warm air.

These factors will allow for Sandy to strengthen 10-20mb (I’m talking central pressure here) once the phase occurs on Monday. Seeing as though I expect Sandy to maintain a pressure of 965 to 970mb until the phase, I still like yesterday’s forecast of a 945-960mb low pressure system hitting somewhere in the Northeast Monday night or Tuesday. Wind wise, this would correlate to a large area of 70-80MPH winds over water, or a category 1 hurricane. These are sustained values, gusts will be higher.

Be Prepared: Preliminary Impact Graphics

Storm surge:

Due to the large wind field that will be associated with Sandy as it approaches the Northeast, a large amount of water will be moved around. As Sandy moves off the Southeast US coastline an easterly flow will allow some water to pile up even south of the expected landfall point. Here, rises will be more negligible. Near and north of the landfall point, which at this point appears to be NJ or thereabout, an extended period of strong onshore winds over a large area will push a lot of water towards the shoreline. It is too early to put specific numbers on the surge threat, however, in the red area, should Sandy remain on the forecast track, storm surge values would be several feet or more, meaning areas on the coastal plain would see several feet of storm surge flooding. This water will be able to pile up for several tide cycles, with the onshore flow increasing Sunday night and not decreasing until Sandy makes landfall on Tuesday. This will coincide with higher than normal lunar tides to maximize the potential storm surge flood threat. Please heed any evacuation orders that may be issued along the Northeast US coastline.

Winds:

Given the large and intense wind field of Sandy, literally the whole Northeast US and adjacent southern Ontario and Quebec will see the potential for damaging wind gusts. As Sandy nears the shoreline, model guidance is indicating a belt of 100+MPH winds about 5,000 feet above the ground to the north of the center of circulation. Due to the stable nature of the airmass, this won’t mix to the ground as efficiently as in normal hurricanes, however to the north of Sandy’s landfall point, hurricane force wind gusts may occur well inland. The biggest risk for hurricane force wind gusts occurring well away from the ocean will be over Southern New England and New Jersey. Areas near the landfall point of Sandy will without a doubt see hurricane force wind gusts along the shoreline.

Farther inland, the pressure gradient will be very tight, and the winds about 5,000 feet above the ground will blow at over 80MPH over a large area. Here, wind gusts to 60+MPH appear likely. Locally stronger winds may occur over the higher elevations of PA and VA and downwind of these higher elevations, assuming the low tracks to the northeast after a NJ landfall.

The pressure gradient will be strong back to the Great Lakes, where tropical storm force wind gusts will be possible.

In general, in the green area, where wind gusts will be “low end tropical storm force,” isolated to scattered power outages may occur. In the yellow area, where wind gusts will be “high end tropical storm force,” more widespread tree and power line damage will likely occur. In the red, where I think hurricane force wind gusts are most likely, power is expected to go out, and some structural damage may occur.

Should the expected strength/track of Sandy change, I will update this wind gust map.

Snowfall:

Due to the cold air that will wrap in to the west of Sandy, very heavy mountain snow is expected as the tropical moisture is thrown back into the cold air. The heaviest snow should occur over the central Appellations from southwestern PA south through WV and far western VA. Here, several feet of wet snow may fall.

Elsewhere, there may just be enough cold air over the eastern Great Lakes and upper Ohio Valley for some snow as Sandy pushes inland. However, this scenario is much more uncertain, so for now will paint in a “low impact” snow event where snow is most likely in these areas.

Rainfall:

As Sandy moves northwestward, it will bring a large slug of tropical moisture. A large swath of 3-6”+ rainfall amounts will occur, and flooding will be possible. Look at the above map to see what the Government’s Hydrometeorlogical Prediction Center expects for rainfall in your area.

I will have another update as details become clearer Saturday Night or Sunday Morning.

After ravaging eastern Cuba as a strong category 2 hurricane last night, hurricane Sandy is zigzagging her way through the central Bahamas with sustained winds of greater than 100MPH. Rain bands from Sandy are also brushing up against the southeastern coast of Florida as the hurricane passes by to the east. Although Sandy is still purely tropical with a tight core of intense winds over the central Bahamas, the hurricane is beginning to interact with an upper level trough which is why the hurricane has such a large mass of clouds associated with it.

Through the weekend, Sandy is expected to pass close to or over the western Bahamas, which remain under a hurricane warning. The hurricane will then turn towards the north-northeast off the southeast US coast, with large, battering waves and a high risk of rip currents occurring through the weekend from southern Florida north through the Carolinas.

As Sandy snakes its way off the southeast coast this weekend, it is still expected to merge with a mid to upper level trough (shown above), causing the cyclone to begin taking on sub-tropical characteristics.  This means that while Sandy will still draw energy from the warm waters of the Gulf Stream, and still maintain strong winds near its center, the system will begin to also draw energy from non-tropical sources such as the jet stream and warm and cold fronts. While this happens, the winds from Sandy will also spread farther away from the tight core, which means that although Sandy will likely weaken to a category 1 hurricane this weekend, it will remain a large and dangerous storm.

Today, two clusters of modeling have developed with relation to Sandy’s track and eventual landfall:

1. The Euro and NOGAPS models show Sandy staying closer to the US coastline and phase the system more aggressively with the diving central US trough, resulting in a landfall into the Delmarva region.
2. The GFS, GGEM (Canadian) and UKMET models forecast Sandy to wander a little farther north before being captured by the incoming trough, resulting in a landfall in the NYC, Long Island or Southern New England area.

There appear to be couple of differences in the modeling that result in these two camps of possible landfall locations:

1. The main difference seems to be the strength of ridging stretching between the ocean low over the open Atlantic and Sandy. The camp that takes Sandy farther north show slightly weaker ridging in this region. The camp that takes Sandy into the Delmarva region show stronger ridging. The GFS (left) and Euro (right) are posted above to illustrate this difference.
2. The GFS, GGEM and UKMET all show Sandy resisting phasing a little bit initially…which can be seen on this graphic below:

This is the GFS model valid Monday morning. As can be seen, Sandy has been captured by the diving central US trough, but instead of being captured and violently phasing with the trough right away, Sandy resists this phasing. This is likely because the model is picking up on Sandy being a much stronger hurricane right now than originally thought, and maintaining a stronger warm core farther north. Strong warm core cyclones are known to initially resist phasing with a cold core trough, because the systems are not alike.

In the end however, all models do eventually show a phasing of Sandy with this northern trough, resulting in a NW motion towards the northeastern US coastline.

Which camp is ultimately correct? Right now, I’d lean towards the camp that takes Sandy into the coast a little farther north, mainly due to the possibility that Sandy will initially resist phasing a little bit, allowing it to get farther north before ultimately sling-shotting towards the northwest. The GFS and European ensembles generally agree on this type of scenario, with a likely landfall zone from NJ northward towards the Boston area, with some risk of a landfall as far south as northern Virginia, with the time-frame for landfall being Monday into Tuesday:

Now that we have established that landfall is likely, and should occur somewhere from Virginia points north Monday into Tuesday, it is time to discuss the possible strength of Sandy as it impacts the northeast US:

There are a few factors that will allow Sandy to go from a sub-tropical storm with winds near hurricane strength to a very deep hybrid storm as it nears the coastline.

Jet Structure:

Two potent jet streaks, shown above by the blue color-fill, will be positioned to provide for a huge amount of lift over the entire Mid Atlantic, Northeast, and near-shore waters as Sandy approaches.

Potential warm-seclusion nature of Sandy near landfall:

If Sandy is able to maintain a strong warm core as it heads northward into early next week, the warm core will be caught under and upper level trough and surrounded by cooler air aloft, as shown above on the GFS. This will allow for a tremendous amount of lift with Sandy due to the buoyant nature of warmer air.

Mid-level height falls, positive vorticity advection:

As Sandy is captured, the low pressure aloft associated with Sandy will combine with the lower pressure aloft created by the incoming trough, to result in pressures, or “heights” aloft to fall dramatically near and over Sandy as it approaches the US coastline. In addition, the mid-level spin, or “vorticity” within Sandy and the trough will combine and create a large amount of vorticity aloft as shown above by the color-fill. This vorticity aloft will also enhance lift.

When you combine the upper level lift caused by the jet streaks and the remaining warm core of Sandy providing for tremendous lift under a very strong low aloft, you have the ability for the storm to really strengthen as it approaches the US coastline on Monday and Tuesday. It is estimated that Sandy’s pressure will hold steady as it moves northward this weekend due to a baroclinic assist, as discussed earlier. Thus, Sandy will likely have a pressure of somewhere around 965-970mb before it begins to interact with the trough. As trough interaction occurs, Sandy will have 12-24 hours of intensification before the pro-intensification factors max out. Thus, it is reasonable to assume Sandy will strengthen 10-20mb after phasing occurs. Doing the math, this results in a potential 945-960mb low pressure system hitting the US coastline on Monday or Tuesday—and many models remain near the strong end of that if not stronger. This will result in a large and strong wind field as Sandy makes landfall.

It is too early to say who will see how much wind; however as a general idea of the wind potential Sandy will carry as it nears the US coastline:

This is the European model’s representation of winds about 5,000 feet above the ground Monday morning in knots. 1 knot equals 1.15 miles. Winds at this speed at 5,000 feet above the ground (80-90 knots) would likely translate to 60-70 knots on the surface, or about 70-80MPH over the water. These types of wind speeds are consistently showing up on our models over the water, with weaker but still dangerous winds potentially spreading well inland with Sandy.

This wind representation will change as the models continue to hone in on a final landfall destination, however there are some key takeaways from this situation:

1. Sandy is likely to impact the Mid-Atlantic and Northeast as a category 1 hurricane Monday and Tuesday, with residual impacts lasting through Wednesday.
2. Sandy will feature an exceptionally large area of tropical storm force winds, likely several hundred miles across, as it makes landfall.
3. Damaging winds are likely along the coastline near and potentially hundreds of miles north of Sandy’s landfall point along the coast. Some wind damage may occur inland as well, although the strongest winds will be near the ocean.
4. Large battering waves and significant storm surge will occur near and north of Sandy’s landfall destination.
5. Significant rainfall will occur over much of the Mid-Atlantic and Northeast, with some rainfall reaching as far west as Ohio and Michigan.
6. A crippling wet snow event remains possible over the Appellations from central PA south through the mountains of WV, Maryland and western VA.

As this event continues to draw closer I will have further updates with more specific impact information.

Hurricane Sandy, the storm projected to eventually impact the east coast of the US, has already hit eastern Jamaica and is now eying eastern Cuba as a hurricane. As can be seen above, the hurricane has developed a small eye with a well-organized ring of cold, intense cloud tops wrapping around this small eye. Sandy is becoming an impressive looking hurricane.

Over the next few days, Sandy will begin to have its early US impact. However, first Cuba will deal with a potent category 2 or 3 hurricane early Thursday morning. Thereafter, on Thursday and Friday, Sandy will snake its way through the central and western Bahamas, potentially as a hurricane—the Bahamian government has issued a hurricane warning for that portion of the island chain. Eastern Florida may also be grazed by Sandy, with breezy conditions and heavy rains likely to end the work-week.

As Sandy moves through the Bahamas and off the southeast US coast it will merge with a mid to upper level trough of low pressure. On the map above, the black lines indicate isobars about 18,000 feet off the ground, and one can see the mid-level low that Sandy, represented by the ball of yellow and orange off the coast of Florida, combines with. While this happens, the winds located approximately 40,000 feet off the ground, represented by the wind barbs on this map, will pierce through Sandy from the south at over 50MPH. This will cause Sandy to acquire sub-tropical characteristics off the southeast US coast as we head towards Saturday. What does this mean?

1. Sandy’s wind field will expand, but initially weaken.
2. Precipitation will spread out farther from the center of Sandy.
3. Sandy will retain a “warm-core,” meaning that heat from the ocean will fuel thunderstorms with Sandy.
4. Sandy will also tap “baroclinic” sources of energy, meaning that it will begin to tap sources of energy from the jet-stream, changes in temperature, and will be more resilient to wind shear and lower sea surface temperatures.

These sub-tropical characterizes will become important, because as Sandy moves just off the southeast coast of the US Saturday and Sunday, it will not only tap the warm waters of the Gulf Stream, it will be near or under portions of three jet-streaks, shown above Sunday afternoon, that will ventilate the storm and provide plentiful lift. This will allow Sandy to maintain strong tropical storm or category 1 hurricane intensity through the weekend as it crawls northward off the southeast coast of the US. This much we know…it’s what happens after Sunday that may impact millions of people.

There are a number of players on the field for this potential major east coast storm. I have highlighted them on this evening’s GFS run, valid early Monday morning:

1. First and forecast, a very large –NAO block over the North Atlantic will force the flow over the northwest Atlantic to turn south-southeast, towards the north-northwest, and in combination with a blocking ocean low, will make it difficult for Sandy to escape out to sea.
2. The PNA over the Pacific and western N. America will go “positive,” which translates to ridging over the western US. This will force pieces of energy south over the northern Plains and Great Lakes, which will carve out a trough over the central US.
3. As the pieces of energy attempt to move east, they will be blocked by the massive –NAO block and will have no choice but to carve out a sharper, deeper, and negatively tilted trough. This will further aid in turning the steering currents towards the north-northwest over the northeastern US and far northwestern Atlantic.
4. Assuming the NAO block is as strong as currently projected on essentially all modeling, Sandy will have no choice but to be caught in these NNW steering currents, and come towards the Mid Atlantic or Northeast US coastline.

Let’s take a look at some of our forecast models and see if they track Sandy in this direction:

This afternoon’s UKMET, shown above, captures Sandy late, and pulls the storm towards Maine as a very strong storm system Tuesday morning.

This afternoon’s GGEM (Canadian) model is very similar, taking a very strong storm system into the Boston area Tuesday morning.

This afternoon’s European model is much faster with the whole scenario and takes a still sub-tropical (and potent) Sandy into the Delmarva Peninsula on MONDAY.

The most recent GFS runs have been interesting. They have shown Sandy trying to escape out to sea, only to be kept in the fray by the large blocking high over the N. Atlantic, and eventually pulled back towards the Canadian Maritimes and New England by the Great Lakes trough that is forced to deepen and pull Sandy back in due to the +PNA ridge over the western US and strong –NAO block.

Regardless of western US ridging and central US trough depth and strength, the operational models have all found a way to sooner or later sling-shot Sandy towards the northeastern US due to the extensive blocking not only preventing the cyclone from escaping, but also forcing a trough to sit and deepen over the Great Lakes and Ohio Valley, which also aids in pulling Sandy in. The GFS, European, and GGEM (Canadian) ensembles all more or less pull Sandy in as well:

GFS ensemble tracks:

European ensemble mean valid Tuesday morning:

GGEM (Canadian) ensembles valid Tuesday morning:

So, this essentially has the unmitigated impact of saying the chances of a major impact from a hybrid tropical-nor’easter are increasing by the day over the northeastern US. Due to the strength of the possible system, strong damaging winds, coastal flooding, heavy rains and potential snow in the mountains of western NY, PA, WV and western VA are all impacts that may be felt from Virginia northward towards Nova Scotia, including the I-95 corridor from Richmond through Boston as early as Monday.

However, it is important to note that this forecast is not quite a certainty:

-If Sandy manages to move farther east than forecast over the Bahamas, it may still be difficult for the block and central US trough to draw it towards the US coastline.

-If the western US pattern ends up significantly flatter than shown, the central US trough may have a harder time deepening enough to capture Sandy. This is the potentially the biggest risk for this big storm forecast.

-If the blocking in the Atlantic ends up weaker than currently projected, it would take an extremely deep trough to capture Sandy.

As we head towards the weekend, this forecast confidence will increase. However, right now it is important to state that a strong storm is likely to track into or very close to the Mid-Atlantic and Northeastern US, and Canadian Maritimes Monday into Tuesday. Whether or not the system actually strikes the US or Canada is still a bit uncertain, but impacts, especially to the marine community, appear increasingly likely.

Right now I’d put the odds at Sandy making landfall over the Mid Atlantic or Northeast at about 60%…the chances of it missing but passing within 100 miles of the coast at 30%…and the chances of it missing by more than 100 miles at 10%.

There is also a chance of a “weaker” nor’easter developing and impacting the Northeast if Sandy stays out to sea, due to the depth of the potential trough over the Great Lakes and Ohio Valley.

I will have another post tomorrow afternoon on this situation.