Sandy We’re in Misery: Storm Recap

Posted on November 3, 2012 by Philip Orton

Hoboken taxi lot under water the day after Sandy’s sojourn to NYC and NJ. Credit: Charles Sykes, AP

Now that Sandy has moved on, and some of us are lucky enough to have power and be getting back to “normal life”, I’m finally writing to recap what happened with the coastal flooding and how the forecasts compared to the observed flood.

Coastal water levels in New York Harbor were the highest in all ~300 years of New York City (and New Amsterdam) history.  The water level at The Battery was 13.9 ft above the average daily low tide level (MLLW) at 9:24 pm EDT, with a peak storm surge of ~9.2 ft coming close to high tide.  This storm tide (water level) of 13.9 ft MLLW is about 5.5 ft above many of the area’s lowest sea walls.

Water levels (WL) for the secondary gauge (primary one failed) at The Battery for Hurricane Sandy, relative to MLLW (average daily low tide), from NOAA/NOS.  Obs-Pred is the “storm surge”.

Sandy’s storm tide beat that of Irene by 4.5 ft, the (80 year) tide gauge record of Hurricane Donna (1960), and the estimated all-time record of about ~13.3 ft from the Hurricane of 1821.  (though some estimate it to be more like 11.2 ft).

The flood elevation at Kings Point (Western Long Island Sound) was ~14 ft a few hours later, with a peak storm surge of ~12.3 ft coming near LOW tide – fortunate!

Our NYHOPS/SSWS webpage is offline due to the power loss in Hoboken, but the last graphical forecast of flood elevations that I have on my laptop (Monday at 10:30 am, posted on this blog) at Battery was low by 22%, and our forecast for Kings Point was low by 10%.  Other forecast models also under-estimated the central forecast, likely in part due to the unusual nature of Sandy (aka “Frankenstorm”) and its surprising strengthening on the last day.  The other models include P-Surge, ET-Surge (also shown here), and Stony Brook).  Some other things we will examine as possible factors with our model’s underestimation of the final storm tide are summarized in a recent paper we published on Irene’s storm tide, and include the “sea surface drag coefficient” that helps represent how well momentum from wind is transferred to the ocean, and the high-bias of the NAM atmospheric model in forecasting a tropical cyclone’s low central pressure (thus causing our model to underestimate the inverse barometer effect).

The forecast range given by NOAA’s National Hurricane Center was very valuable for decision-makers and the public, as they have a probability-oriented product that gives percent-likelihood exceedance levels.  They used those results to predict a storm surge 6-11 ft, and the surge was 9.3 ft at The Battery and 12.0 ft at Kings Point.   Stevens Institute doesn’t make probabilistic surge forecasts, but we’ve had preliminary signs that we’ve secured funding with a recent proposal to develop such a product.

(click to see) Animation of GOES infrared satellite data showing cloud top temperatures for Sandy as she made landfall in New Jersey Oct 29, 2012 (Credit: University of Wisconsin).
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Large oil spill in NY harbor delays port opening

Posted on November 2, 2012 by juliepullen

A significant oil spill in NY harbor is keeping the critical Arthur Kill closed indefinitely.  The Coast Guard reports that the diesel leak from a fuel terminal was contained November 1.  The rupture occurred as a result of Hurricane Sandy and has been called a “catastrophic failure of tanks” by Rear Adm Abel.  Clean-up continues on the estimated 300,000 gallons of fuel.  NOAA and Coast Guard are responding and the Coast Guard Atlantic Strike Team has been deployed.

The Arthur Kill separates Staten Island from New Jersey and holds crucial oil supply infrastructure.  It is the passageway for container ships to reach Port Newark.  Clean-up of comparable spills has taken 1-2 weeks.  Terminals in the port sustained damage during the storm, including the flooding of the Philips 66 terminal on the Arthur Kill.  The Kill Van Kull was re-opened for vessel traffic today (November 2), but the Arthur Kill remains closed.  Addressing both the damage to the port infrastructure and the oil spill are necessary for fully re-opening the port to all shipments.  (More details on the status of the oil terminals here.) Popular Science today has an overview of the situation.

The Captain of the Port based at the Coast Guard station on Fort Wadsworth, Staten Island closed the Port of New York and New Jersey beginning Monday October 29 at 7 am.  This closure of the port, extending a week, is believed to be the longest.  The port of NY & NJ is the largest oil importing port in the country and the largest container port on the east coast.

NY harbor, normally bustling with vessel traffic, is quiet Friday afternoon. In the distance, vessels are moored awaiting entrance to the harbor.

Incidentally, jet fuel for the 3 NYC area airports is supplied by Buckeye Pipeline through Linden (NJ) Station.  Today that facility is transferring from generator power to main power. (From Department Of Energy Hurricane Sandy Situation Report # 11 November 2, 2012 (3:00 PM EDT))

Riverkeeper has been warning about water quality in the city’s waterways as a result of Hurricane Sandy.

 

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Upcoming Presentation on Surges, Barriers and Coastal Restoration

Posted on November 1, 2012 by Philip Orton

I have an oral presentation at the American Geophysical Union Fall Conference in San Francisco, December 4th, 3:25-3:40 pm.  It is particularly timely, given the destruction left by Sandy and the growing discussions about storm surge barriers.  And similarly, don’t forget that there is the Kerry Emanuel NYC hurricane risk lecture Nov 15th at Columbia (public) with attendance by registration only.

CONTROL ID: 1502631
TITLE: Contrasting NYC Coastal Restoration and Storm Surge Barrier Impacts on Flooding
AUTHORS (FIRST NAME, LAST NAME): Philip Mark Orton2, 1, Nickitas Georgas2, Alan F Blumberg2
INSTITUTIONS (ALL): 1. Maritime Security Laboratory, Stevens Institute of Technology, Hoboken, NJ, United States.
2. Center for Maritime Systems, Stevens Institute of Technology, Hoboken, NJ, United States.
ABSTRACT BODY: A detailed and well-validated hydrodynamic model is used to examine the potential effects of storm surge barriers and Jamaica Bay restoration on coastal flooding in New York City (NYC). The most recent flooding episode, the August 2011 tropical cyclone Irene, is utilized as a test case. Two experiments are run: (a) adding three storm surge barriers, and (b) reducing the depths of channels in Jamaica Bay towards their historical levels before extensive dredging took place. Results show that the surge barriers are an effective method for protecting the city center, but have a negative result of raising flood elevations outside the barriers. The rise is ~5% in the Jamaica Bay watershed, where most of NYC’s low-lying vulnerable population is located. Shallowing Jamaica Bay reduces Irene’s peak storm tide elevation by ~12% in the Bay, reduces normal high tide elevations, but also raises low tides and overall mean water levels. The reduction in storm tide flood elevations is enough to offset decades of anticipated sea level rise. In recent decades, tidal marsh islands in the Bay have been rapidly eroding. Further research should examine how the marshes would adapt to a managed long-term shallowing plan, as well as how their re-growth could provide additional flood protection.
KEYWORDS: [4564] OCEANOGRAPHY: PHYSICAL / Tsunamis and storm surges, [4534] OCEANOGRAPHY: PHYSICAL / Hydrodynamic modeling, [4332] NATURAL HAZARDS / Disaster resilience, [1641] GLOBAL CHANGE / Sea level change.
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Updated Forecasts from SSWS and ET-Surge

Posted on October 29, 2012 by Philip Orton

Our Stevens Storm Surge Warning System have been predicting flood elevations about a foot below the observations, so take this as a low-end estimate, but here are those predictions.  Also plotted are NOAA’s ET-SURGE predictions, which have a similar estimated peak water elevation for The Battery and a lower one for Kings Point.  Also, the storm is apparently strengthening, so this will likely be revised upward as the afternoon progresses – the next forecast update is at 4:30pm.

I recommend you pay the most attention to the prior blog post, below this one, as that has forecast ranges of flood elevations and translations into what that might mean in NYC and area neighborhoods.  When it comes to life and limb, better to look at the cautious conservatively high predictions…

Stevens NYHOPS Storm Surge Warning System forecast for water levels at The Battery in New York Harbor (magenta), relative to mean sea level (LMSL). Predicted tides are also shown (blue), as well as observed water levels and the NOAA ET-Surge forecast for comparison (green).  Add 2.6 ft to heights at  The Battery to get MLLW reference (average daily low tide).

And for Kings Point …

Stevens NYHOPS Storm Surge Warning System forecast for water levels at Kings Point in Western Long Island Sound (magenta), relative to mean sea level (LMSL). Predicted tides are also shown (blue), as well as observed water levels and the NOAA ET-Surge forecast for comparison (green).

Let’s hope these model predictions are the highest we see.

These figures nicely illustrate the time-dependence of the problem — when the high tide and peak water levels hit, as well as how the tides are crucial to the floods — at Battery, the current timing of the peak surge (and basically, storm landfall of NJ) is at high tide.  At Kings Point, the forecast is for the peak surge to come before high tide, so water levels are not as likely to break records.

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What Height to Expect from this Evening’s Deluge

Posted on October 29, 2012 by Philip Orton

We are looking at a coastal flood around New York City region tonight that is nearly certain to be record-breaking.  The morning flood at The Battery and other nearby locations was close to the flood elevation of Irene, and only about a foot lower than the record-setting flood there of Hurricane Donna (1960).   We may even best the highest flood elevations in NYC history, which occurred in 1821.  This morning’s flood elevations are a useful preview of what will occur this evening as Sandy’s worst comes our way — expect roughly 2-7 ft higher flood elevations, and find high enough ground to be safe from the higher end of that, just in case!

NHC forecast track for Hurricane Irene, including the storm surge heights that have a 30% likelihood of being exceeded (data from NOAA’s National Hurricane Center’s P-SURGE). Courtesy of Dr. Nickitas Georgas.

I am basing this on the range of expected storm surge, 6-11 ft, as well as the fact that the flood is likely to come near high tide at 8:48 pm, which adds 2.4 feet more (relative to mean sea level, MSL, similar to NAVD88).  This total water elevation (storm tide) is 8.4-13.4 ft above MSL whereas 7.4ft above MSL is the record elevation from 1960’s Donna.  That is, this flood is likely to beat the Battery record by 1 to 6 ft!  And the estimates of the 1821 flood elevation are roughly 11 ft above MSL, so we may even best that approximate level that is thought to be the highest in all ~400 years of New York City (and New Amsterdam) history.

This is no celebrating matter, as this puts seawater roughly 2.5 to 7.5 ft above the city’s lower seawalls and deep water may quickly come into the city’s lower neighborhoods.

Make no mistake — this isn’t just a concern for Evacuation Zone A, it could be a danger to people at low elevations in all the Evacuation Zones.  People in basement apartments or on the first floor should be ready and watching out this evening for floodwaters, and have a plan for quickly getting to a higher floor if they aren’t already “evacuating” to a friend’s apartment.

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Dangerous, Likely Recordbreaking Surge Coming to NYC

Posted on October 28, 2012 by Philip Orton

Wind forecast (scale in knots) for 7pm Monday, from NOAA’s North American Mesoscale (NAM) model, showing winds blowing into NY Harbor at 45-55mph (red color) and even 55-65mph (magenta). The eye of the storm is the region with weak winds (white).  (created with the Weather Underground map tool).

Sandy’s storm surge for New York Harbor is almost definitely going to be worse than Irene’s, and it is likely to cause several feet higher flooding.  There is a good chance (about 50%) that flood elevations at Manhattan and nearby New Jersey will be the worst in 80 years of measurements, and if so, then likely the worst since the devastating 1821 hurricane.  Strong uncertainty exists, in part because the timing of the flood relative to high tide can make all the difference.

Some flooding will come with high tide as early as Monday morning, but the worst is expected at the next high tide on Monday evening, and another wave of flooding may come Tuesday morning.  The storm forecast has shown little change today — it is expected to make landfall as an extra-tropical storm similar to a very large Category 1 hurricane with maximum winds of about 70-80 mph, running a northwestward course over the middle of the New Jersey coast.  The latest weather guidance suggests it may make landfall at high tide on the Jersey Shore, another “worst case” factor for that area as well as New York City, where high tide is 8:53 pm.

This storm will be very large, and strong onshore winds of over 50 mph will likely extend hundreds of miles off toward “the right of the storm” as its center makes landfall. This suggests widespread flood impacts, not only localized impacts near the center of the storm.

Storm surge guidance – key points:

The NYHOPS Storm Surge Warning System forecast for the NY/NJ Harbor and New York City region has been for Sandy’s coastal flood height to be similar to or a few feet higher than Irene, which itself flooded into the city’s low-lying neighborhoods.  (However, if you prefer REALLY scary stories, take heed of the 10% likelihood flood forecast I describe further below, if you want to know what is a sort-of a “worst-case scenario”).

Stevens NYHOPS Storm Surge Warning System forecast for water levels at The Battery (magenta), relative to mean sea level (LMSL – NOTE THIS IS A CHANGE FROM PRIOR PLOTS). Predicted tides are also shown (blue), as well as observed water levels and the NOAA ET-Surge forecast for comparison (green).

Above is a figure showing the NYHOPS and NOAA forecasts for Battery Park — the New York/ New Jersey Harbor region – 7.1 ft above mean sea level.  This is about 1-2 ft above some low seawalls around the city; a few inches higher than Irene’s flood level.  The surge doesn’t coincide with the high tide in this forecast, but if the storm comes a few hours earlier, then the total water level will be a few feet higher.

Above is the forecast for Kings Point and other areas in Western Long Island Sound and the eastern end of East River (e.g. Flushing) – 10.4 ft above local mean sea level; this is roughly 2.5 ft ABOVE Irene’s flood elevations.

“The 10% likelihood exceedance” flood elevation

However, one should take heed of the NOAA P-SURGE 10% likelihood exceedance storm surge forecast, which is sort of like a mild version of a worst-case scenario forecast. That currently shows there is a reasonable possibility for Sandy to be about 4-5 feet higher than these forecasts.

NOAA’s probabilistic surge (P-Surge) forecast of a 10% likelihood storm surge amplitude. To estimate total water levels, add this value to the tide height at the time of peak surge.

For a good estimate of a “worst-case scenario” total water elevation, add this to the high tide elevation, but subtract 1 ft because they use an old height datum (NGVD29) and that is close to a foot below mean sea level.  In this case you get a total of about 11.5 ft above mean sea level for The Battery, or 13 ft for Kings Point, both shattering existing records and sending water 5-6 ft above seawalls and deep into the city’s neighborhoods (beyond Evacuation Zone A).

It concerns me greatly that I’m hearing of people ignoring evacuations, and I’m seeing apartments on my street that are below sidewalk level that aren’t in the evacuation zone.  The sidewalks are about 10 ft above mean sea level, so there is the potential for some people to get waterfalls of endless ocean water coming into their homes tomorrow evening.  Look out for your neighbors, and spread the word about what the flood forecast means in your low-lying neighborhood!

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Sandy’s Storm Surge Forecast Interpretation: Steady and Not Good

Posted on October 28, 2012 by Philip Orton

The forecasts are gradually steadying for the storm surge flood elevations for Sandy, but strong uncertainty exists because the timing of the flood relative to high tide can make all the difference … The “central forecast” for the storm is for it make landfall as an extra-tropical storm similar to a very large Category 1 hurricane with maximum winds of about 70-80 mph, and run a northwestward course across the center of New Jersey’s coast. This storm track is more-or-less a worst-case scenario for NYC flooding. Below I will briefly summarize what our storm surge forecasts say we can expect, as well as what we see as the worst-case scenario for flood elevations.

Bur first, in plain English: Coastal flooding for coastal areas within roughly 100 miles north and east of the storm will most likely be severe and damaging, roughly similar to Irene’s flood and going over seawalls and over beaches that lack protective dunes. And at the more extreme end, with lower probability, flood levels could be about 6 feet above area seawalls and even surpass coastal dunes, causing even more severe destruction and extending far inland into low-lying areas. Some flooding could come as early as Monday morning, but the worst is expected Monday evening. Another wave of flooding may come with Tuesday morning’s high tide.

Our NYHOPS/SSWS system’s forecast is in general agreement within a foot or two of the forecasts of NOAA’s ET-Surge (shown in plots below) and Stony Brook’s surge model, so models are coming into much better agreement.

This storm will be very large, and strong onshore winds of over 40 mph will likely extend hundreds of miles off toward “the right of the storm” as its center makes landfall. This suggests widespread flood impacts, not only localized impacts near the center of the storm.

Storm surge guidance – key points:

The NYHOPS Storm Surge Warning System forecast for the NY/NJ Harbor and New York City region is for Sandy’s coastal flood height to be similar to or a few feet higher than Irene, which itself flooded into the city’s low-lying neighborhoods. (However, if you prefer REALLY scary stories, take heed of the 10% likelihood flood forecast I describe further below, if you want to know what is a sort-of a “worst-case scenario”).

Stevens NYHOPS Storm Surge Warning System forecast for water levels at The Battery (magenta), relative to mean lower low water (MLLW – normal daily low tide). Predicted tides are also shown (blue), as well as observed water levels and the NOAA ET-Surge forecast for comparison (green).

Above is a figure showing the NYHOPS and NOAA forecasts for Battery Park — the New York/ New Jersey Harbor region – 9.4 ft above MLLW (typical low tide level), 6.7 ft above local mean sea level (near NAVD88). This is about 1-2 ft above some low seawalls around the city; about the same as Irene’s flood level.

Stevens NYHOPS Storm Surge Warning System forecast for water levels at Kings Point in Western Long Island Sound (magenta), relative to mean lower low water (MLLW – normal daily low tide). Predicted tides are also shown (blue), as well as observed water levels and the NOAA ET-Surge forecast for comparison (green).

Above is the forecast for Kings Point and other areas in Western Long Island Sound and the eastern end of East River (e.g. Flushing) – 15.0 ft MLLW, ~11 ft above local mean sea level; this is roughly 3 ft ABOVE Irene’s flood elevations.

“The 10% likelihood exceedance” flood elevation

However, one should take heed of the NOAA P-SURGE 10% likelihood exceedance storm surge forecast, which is sort of like a mild version of a worst-case scenario forecast. That currently shows there is a reasonable possibility for Sandy to be about 4-5 feet higher than these forecasts.

NOAA’s probabilistic surge (P-Surge) forecast of a 10% likelihood storm surge amplitude. To estimate total water levels, add this value to the tide height at the time of peak surge.

For a good estimate of a “worst-case scenario” total water elevation, add this to the high tide elevation, but subtract 1 ft because they use an old height datum (NGVD29) and that is close to a foot below mean sea level. In this case you get a total of about 14 ft above MLLW (typical low tide) for The Battery, or 17 ft for Kings Point, both shattering existing records and sending water 5-6 ft above seawalls and into the city’s low-lying neighborhoods.

This could happen if the storm winds up making landfall with stronger peak winds than are currently predicted, perhaps as a strong Cat-1 hurricane with peak winds from 80-90 mph. These would be by far the highest flood elevations in the 80 years that records have been kept, and unless efforts are taken to protect vulnerable infrastructure, this would definitely cause some subways, highway tunnels, and electrical infrastructure to be filled with salt water and shut down for weeks.

The Stevens NYHOPS Storm Surge Warning System is re-run with the latest weather forecast every six hours, so visit again to check for updates, and STAY DRY!

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Sandy’s Flood Forecast Gets Bleaker (and Bleeker?)

Posted on October 27, 2012 by Philip Orton

Our six-hour update just came in and it’s not good news for New York City and areas of New Jersey inside NY/NJ Harbor — the model forecast for Monday night rose two feet higher at The Battery, so now it calls for a flood elevation of 10.8 ft above MLLW (normal daily low tide), which is 1.3 ft higher than Irene’s flood elevation and about 3 ft above the area’s lowest seawalls.  This is bad news, but the forecast is still highly changeable.

Stevens NYHOPS Storm Surge Warning System forecast for water levels at The Battery (magenta), relative to mean lower low water (MLLW – normal daily low tide).  Predicted tides are also shown (blue), as well as observed water levels and the NOAA ET-Surge forecast for comparison (green).

The flood elevation is a combination of a 6.5 ft storm surge coinciding with the time of a high tide, so slight changes to storm surge timing could help reduce the forecast water level.  The forecast flood elevation at Kings Point is still about 13 ft, but it is noteworthy that it would be a 7 ft storm surge that is arriving three hours before the time of high tide, so it could be worse with a slight delay in arrival time.

If the Battery forecast should hold or worsen, these would be the highest flood elevations in the 80 years that records have been kept at that location.  Unless efforts are taken to protect vulnerable infrastructure, this would cause some subways, highway tunnels, and electrical infrastructure to be filled with salt water and shut down for weeks.  And beyond that, I would estimate the 10% likelihood exceedance flood elevation (sort of like a mild version of a worst-case scenario) for Sandy to be about 3 feet higher than this forecast.  This could occur if the peak surge coincides with high tide and the storm ends up making landfall with stronger peak winds than are currently predicted.

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Sandy/Frankenstorm Storm Surge Forecast Interpretation

Posted on October 27, 2012 by Philip Orton

Here comes Hurricane Sandy, aka Frankenstorm — The “central forecast” for the storm is for it make landfall as a Category 1 hurricane with maximum winds of about 70-80 mph, and run a northwestward course over Southern New Jersey.  Quite importantly for our storm surge forecast, this storm starts like a bad nor’easter and ends like a hurricane, so the storm surge will be building up all day on Monday.  Below I will briefly summarize what our storm surge forecasts say we can expect, as well as what we see as the worst-case scenario for flood elevations.

Bur first, in plain English:  Coastal flooding will probably will be similar to what we had with Irene, but the weather forecast is still not very clear — at worst, flood levels could be several feet above area seawalls and coastal protective dunes, so keep checking back for our latest updates.  Flooding could come as early as Monday morning, but the worst is expected Monday evening.

The weather forecast is still having that “uncertainty problem” — the range of all the different forecast models is large, and some predictions suggest the center of the storm might hit as far east as Eastern Long Island, while others say as far south as the Delmarva peninsula (or the Maryland-Virginia border).  Uncertainty is slowly decreasing as the storm gets closer, so keep checking in for updates.  Regardless, the storm will be very large, and strong onshore winds of over 40 mph will likely extend hundreds of miles off toward “the right of the storm” as its center makes landfall.  This suggests widespread flood impacts, not only localized impacts at the center of the storm.

Storm surge guidance – key points:

The NYHOPS Storm Surge Warning System forecast for the NY/NJ Harbor and New York City region is for Sandy’s coastal flood height to be similar to Irene, with about a foot lower in some places and about a foot higher in others.  (However, if you prefer scary stories, take heed of the 10% likelihood flood forecast I describe further below, if you want to know what is a sort-of a “worst-case scenario”).

Stevens NYHOPS Storm Surge Warning System forecast for water levels at The Battery (magenta), relative to mean lower low water (MLLW – normal daily low tide).  Predicted tides are also shown (blue), as well as observed water levels and the NOAA ET-Surge forecast for comparison (green).

Above is a figure showing the NYHOPS and NOAA forecasts for Battery Park — the New York/ New Jersey Harbor region – 8.9 ft above MLLW (typical low tide level), 6.2 ft above local mean sea level (near NAVD88).  This is about 0.4 ft above some low seawalls around the city; about 0.6 ft below Irene’s flood level.

Stevens NYHOPS Storm Surge Warning System forecast for water levels at Kings Point, far Western Long Island Sound (magenta), relative to mean lower low water (MLLW – normal daily low tide).  Predicted tides are also shown (blue), as well as observed water levels and the NOAA ET-Surge forecast for comparison (green).

Above is the forecast for Kings Point and other areas in Western Long Island Sound and the eastern end of East River (e.g. Flushing) – 12.0 -13.5 ft MLLW, 8.0-9.7 ft above local mean sea level; this is roughly 0-1.5 ft above Irene’s flood elevations.

For Western Long Island Sound and even possibly into East River, flood elevations are looking to be worse due to the strong northeast winds blowing down Long Island Sound that will precede the storm’s arrival.  Flood elevations for these areas are forecast to be about a foot higher than they were for Irene.

“The 10% likelihood exceedance” flood elevation

However, one should take heed that we estimate the 10% likelihood exceedance flood elevation (sort of like a mild version of a worst-case scenario) for Sandy to be about 5 feet higher than these forecasts.  This could occur if the storm winds up making landfall with stronger peak winds than are currently predicted, perhaps as a strong Cat-1 hurricane with peak winds from 80-90 mph.  These would be by far the highest flood elevations in the 80 years that records have been kept, and unless efforts are taken to protect vulnerable infrastructure, this could cause some subways, highway tunnels, and electrical infrastructure to be filled with salt water and shut down for weeks.  Until we see forecasts that give more certainty that this will not happen, the population and city officials should be preparing as though these higher flood elevations will occur.  We don’t use our model to quantify this 10% likelihood event — it is based on our model forecasts and expert judgement — but we are seeking funding to develop such a product.

The Stevens NYHOPS Storm Surge Warning System forecast extends three days from each night at midnight, and is re-run with the latest weather forecast each six hours.  It typically shows up about 6 hours after the new forecast comes out, due to the time it takes for model runs and graphics productions – so, look for Tuesday’s forecast any time after 6am on Sunday.

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Spring Tides and Perfect Storms

Posted on October 25, 2012 by Philip Orton

Map of winds during the Perfect Storm of late October, 1991. Color shading shows wind speed (in meters per second, roughly double it to get knots or mph).  The storm caused what has been estimated as “500-year” flood elevations storm surge for Boston.

A storm with similarities to the Perfect Storm of 1991 is expected to come northward by early next week and may make landfall in the Northeastern U.S. or Canadian Maritimes.  Some have been mentioning that the storm would arrive near the full moon and thus spring tide, so I wanted to make a quick post explaining that predicted the tide ranges for the New York City region aren’t going be too bad during this period.

Total water elevation at the coast, called the “storm tide”, is driven up by winds and low atmospheric pressure (components of “storm surge”), as well as the astronomical tides.  Tides are predictable, as they are driven by the regular periodic orbits of the earth around the Sun and the Moon around the Earth, as well as Earth’s rotation.  The tides predicted to be present early next week are slightly larger than average, due to it being a “spring tide” — a twice-monthly occurrence when the sun and moon’s gravitational forces are working constructively to create larger tides.

However, this spring tide will actually be a weaker one than many, so the tide’s contribution to total water level isn’t going to be as bad as one might think — the tide range for spring tides varies from month-to-month for multiple astronomical reasons.  The tide range will be only a little bit above average, actually — a range of 5.4 feet at Battery Park on Monday Oct 29, in contrast to the last spring tide (Oct 17) that had a predicted range of 6.5 feet.  Average tide range for Battery Park is about 4.9 ft.

Heights relative to mean-lower-low-water (MLLW; average daily low tide level) — Predicted  (astronomical) tides, observed total water levels (WL), and the anomaly (Obs-pred) at The Battery for October, 2012.  The anomaly is mainly storm surge but can also include rainfall, freshwater from river inputs, and other minor influences.

There is still a great deal of uncertainty on where the storm will hit, and how big a storm surge will be driven up by its strong winds.  If the storm ends up approaching our region, people can visit http://stevens.edu/SSWS for water elevation predictions, and this blog for commentary and interpretation.

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