Vulnerable Northeast SLOSH Scenarios

Yesterday on Facebook I was admiring some graphics posted by Michael Laca, which using computer generated scenarios, depicted SLOSH (Sea, Lake, and Overland Surge from Hurricanes) inundation "worst-case" storm surge situations for several locations in Florida. Michael, a veteran hurricane chaser with over 25 years experience, runs the website TROPMET.COM, and after seeing these startling graphics my interest was immediately sparked to see what would happen "if" a major hurricane barreled into a northeast location from New Jersey to Cape Cod, including New York City. Michael gladly helped me out and produced the SLOSH inundation maps below using the MOM (Maximum Of Maximum) algorithm for each surge basin, which is agnostic of a specific track.

A couple things to note: The SLOSH analysis typically considers hypothetical scenarios – from 10 different directions, four forward speeds, five intensities and 10 to 20 landfall points within a basin, resulting in anywhere from 2,000 to 4,000 combinations of storm scenarios. The program then analyzes each combination and generates a MEOW (Maximum Envelope of Water) for all variations of similar scenarios (such as a category 4, moving northwest at 15 mph, making landfall at 20 different locations within the basin), and then retains the highest surge value at each grid square. The MOM then preserves each of the highest values from each MEOW, resulting in a graphic depicting the highest surge value for any point within the basin across all possible combinations of storms.

So what does that all mean? The maps below show the worst-case scenario at any one point when you consider ALL possible scenarios. That does not mean that for one specific storm scenario, that all areas shown in these maps will experience a "worst-case" surge, since each storm's size, strength, and forward speed will dramatically change the inundation at any particular location. It should also be stressed that these maps are only intended as guidance and should not be used to make decisions on specific evacuations always listen to emergency management and local officials when it comes to an actual event.



Worst case scenario for Manhattan / Hudson River, New York. Exceptionally high surge values of 30–32 feet above MSL (Mean Sea Level) can be expected in several locations, with widespread inundations between 20–25 feet experienced elsewhere.



Worst case scenario for Long Island, New York. Exceptionally high and widespread surge values of 30–33 feet above MSL can be expected along Atlantic facing coastal locations, with extensive inundations between 15–20 feet experienced elsewhere.



Worst case scenario for western Long Island, New York. Exceptionally high and widespread surge values of 30–33 feet above MSL can be expected along Atlantic facing coastal locations, with extensive inundations between 15–20 feet experienced elsewhere.



Worst case scenario for New Jersey / Delaware Bay. Highest surge values of 18–20 feet above MSL can be expected in several locations, with extensive inundations between 10–15 feet experienced elsewhere.



Worst case scenario for Providence, Rhode Island / Cape Cod, Massachusetts. Extremely high surge values of 35–39 feet above MSL can be expected in isolated locations at the heads of rivers and bays, with widespread inundations between 15–20 feet experienced elsewhere.

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Computer Models Define Tricky Forecast

We at The Northeast Quadrant are not card-carrying meteorologists but we do know a lot about weather. And that starts with a basic understating of forecasting. We know that in situations like today when everyone’s eyes and ears are set on an impending winter storm that has yet to form, that we must look at the computer models, and only base our knowledge of the situation on what they are telling us.

I hear the buzz around the office today and I am sure it’s the same for all who commute into Manhattan – “what is in store for me tomorrow? And Friday?”

In my office we have people commuting from Long Island, New Jersey, upstate New York. Even from Pennsylvania. Well, the answer for all of them is different. It is absolutely guaranteed that tomorrow morning each one of us will wake up with another story when we look outside. And another story when we get to work, if we get to work.

If you turn on any weather station or throw any weather-related URL in your address bar you will probably hear a variety of forecasts, all which draw no real conclusion. At least not the conclusion you want to hear, such as:

• It’s going to be a close call for New York City
• The rain snow/line will be very close to New York
• New York and points north and west will likely see all snow
• Long Island and coastal Connecticut will likely see a changeover to rain
• New York may see 6-12 inches
• New York May see a foot plus
• New York may see several inches of snow, then rain, then more snow
• New Jersey will see over 2 feet of snow in the higher elevations

How frustrating, right? The deal is… this storm is so amazingly complex that just a few miles will make a difference in precipitation type and amount. Literally speaking, this time tomorrow there may be a raging snowstorm in downtown New York City, while just several miles away in Nassau County, Long Island there may be a heavy, windswept rain. Same holds true for areas in New Jersey. While there may be a blizzard of epic proportions in the northwestern parts of the state, the coastal areas may see a mix of rain and snow limiting accumulations there.

OK, so you get the picture. But the reason for this post is to show you that when a storm has not even formed, speculations like the above can only be made from computer analysis.

Here are two very reliable computer models that tell us two very different stories:

• The 12Z NAM shows a foot of snow around the New York City area, while the 12 GFS shows only about six inches
• The 12Z NAM shows about four inches across western Long Island, while the 12 GFS shows about eight inches
• The 12Z NAM shows about sixteen inches in northeastern New Jersey, while the 12 GFS shows about ten inches
• The 12Z NAM shows about four inches in southwestern Connecticut, while the 12 GFS shows about eight inches
• The 12Z NAM shows about fifteen hear Philadelphia, while the 12 GFS shows about eight inches



All in all, this will continue to be a tricky forecast that will not be nailed down until tomorrow when the storm develops.

Enjoy the weather – it’s the only weather you got!