Unraveling the Sandy Storm-Surge Forecast

By: Bryan Norcross , 4:36 AM GMT on December 17, 2012

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The track forecast for Sandy has been widely acclaimed as a success of modern meteorology, and rightly so. The advance notice provided by the European Center’s ECMWF computer forecast model was truly remarkable. And the National Hurricane Center’s forecast showed an alarming threat to the Northeast 4 1/2 days before the worst of Sandy’s surge came ashore. But the little-discussed National Weather Service storm-surge forecast for New York and New Jersey was a jumble of confusing and conflicting numbers – a victim of a broken system of forecasting and communicating the threat from rising water. With critical decisions on evacuations in the balance, city and state officials needed a specific, clear assessment of the threat to coastal sections. But based on the publicly distributed bulletins, they didn't get it.

Those of us who have been critical of the National Weather Service’s handling of the storm have focused on the government’s communications protocols and procedures that resulted in no Hurricane Warning being issued for the coastline north of North Carolina. But the real measure of failure was the stunning misunderstanding of Sandy’s threat by the top people in New York City. In addition, those officials in the Northeast and Mid-Atlantic that understood that a dangerous event was unfolding got started too late to execute a fully successful evacuation-communications plan. Beginning the discussion of evacuations just the afternoon before people over a vast area need to leave home would never have produce the best possible end result.

Early this month, the New York Times reported on the shocking decision by city and state health commissioners to leave nursing-home patients in the evacuation zone, even after the Mayor announced that everyone else should leave. Normally the frail and elderly are the FIRST to be moved. Health officials cited “confusing and changing forecasts”, which sounds like a lot of CYA, but they have at least a partial point.

Friday – The First Decision Day

According to the Times, Friday, October 26, three days before the worst of the storm, was a key decision day for city health commissioners. The report says that a “well-organized evacuation…would have taken at least two days”, meaning it would have had to start the next day, Saturday. The commissioners and the city administration were getting direct internal briefings from the National Weather Service – a meteorologist from the local NWS Upton office was embedded at emergency management. We don’t know exactly what was conveyed privately, of course, but the impression that Sandy would NOT be a historic event and instead be no worse than Irene conforms with the public messages from the Upton office.

On Friday morning, Upton’s Area Forecast Discussion (AFD) – where NWS forecasters share their forecast reasoning – used the word MINOR to describe the worst of the expected storm surge in some unfortunate wording:

A FULL MOON IS EXPECTED FOR MONDAY. A STRENGTHENING EASTERLY FLOW WILL AT THE LEAST RESULT IN A MINOR COASTAL FLOOD EVENT SUN INTO TUE...WITH THE POTENTIAL FOR WIDESPREAD SIGNIFICANT COASTAL FLOODING BASED ON THE TRACK OF A COASTAL STORM ASSOCIATED WITH
TROPICAL CYCLONE SANDY.

The “minor” wording was used in 10 AFD updates through the day on Friday until 3:54 pm when the descriptive word was changed to “moderate”:

WIDESPREAD MODERATE COASTAL FLOODING IS POSSIBLE BY THE MONDAY NIGHT HIGH TIDE CYCLE AS THE STRONGEST WINDS BEGIN AFFECTING THE AREA. THEN THE EXACT TRACK/TIMING AND EVOLUTION OF SANDY WILL DETERMINE THE MAGNITUDE OF COASTAL FLOODING WITH THE TUESDAY MORNING/EARLY AFTERNOON HIGH TIDE...WITH POTENTIAL FOR SIGNIFICANT AND WIDESPREAD COASTAL FLOODING RESULTING IN FLOODING/DAMAGE IN HISTORICALLY FLOOD PRONE SPOTS.

This appears to be the “moderate” language that the health commissioners digested to make their decision. If the nursing homes were not in “historically flood-prone spots”, the impression conveyed by the National Weather Service was, apparently, that they would NOT be flooded.

In addition, we know that the internal briefings from the NWS included language comparing Sandy to Hurricane Irene. During Irene just a year before, the flood threat was also characterized by the NWS as “moderate”, so you see the confusion. In the end, of course, Irene did NOT cause the type of flooding that needed an evacuation. The memory of Irene seems to have been a key player in the decision making.

This whole line of thinking and wording from the NWS Upton forecasters is baffling. First, Sandy was ALWAYS forecast to be stronger than Irene, and second, it was on a track that would produce more storm surge, even if it were the same strength. Everybody that has studied the New York/New Jersey hurricane threat knows that a storm center heading toward the west or northwest into New Jersey is the worst-case track for surge. Irene was weaker and NOT on that worst-case track, so why not make the comparison clear?

The key communications point should have been that Sandy was expected to produce a higher storm surge, perhaps significantly higher, than Irene. Period. End of story. End of confusion.

So the key decision day passed without clear, emphatic public language outlining the extreme threat. You might say that the caveats of a chance of “significant flooding” should have been enough to prompt an evacuation order. But forecasters often throw in worst-case language for public consumption, but say in private that they are really expecting a non-worst-case outcome. We can’t tell which way the Upton forecasters were leaning from the Friday language, but we find out Saturday morning.

Saturday Morning

At 5:46 AM, the Upton office issued a Coastal Flood Watch for the entire coastline. The “moderate” language continued:

WIDESPREAD MODERATE FLOODING ASSOCIATED WITH THE HIGH TIDES MONDAY COULD LEAD TO WIDESPREAD FLOODING OF VULNERABLE AREAS ALONG ALL THE COAST LINES.

So “historically flood-prone spots” became “vulnerable areas”, but it was still a pretty weak statement given the threat. And, they gave some hard forecast numbers for the first time, which tell you which way they were leaning on the “moderate” scale. They also threw in some more CYA, which was barely accurate:

TIDAL DEPARTURES… 2 TO 3 FT ABOVE ASTRONOMICAL TIDES MONDAY MORNING INTO TUESDAY MORNING...WITH POSSIBLE HIGHER DEPARTURES DEPENDENT UPON THE TRACK OF SANDY.

In actual fact, a significant change in Sandy’s track would have resulted in approximately the SAME storm surge, but more importantly, 2 to 3 feet is significantly LESS than Irene, which came in at more than 4 feet. As we’ve seen, the Irene comparison was critical for evacuation decision making, so this was a good-news forecast. At its peak, Upton thought that Sandy was most likely to produce less surge than Irene.

And there’s more. The bulletin also included another number, the forecast for water rise “above MLLW” for lower Manhattan Monday morning. For comparison, Irene’s storm tide was 9.5 feet above MLLW.

THE BATTERY NYC.....831 AM.....8.7.......MODERATE

MLLW means, essentially, LOW tide. And remember, the forecast was for Sandy to peak around HIGH tide. So, good luck to the poor non-meteorologist decision maker who has to sort out tidal departures from MLLW from high tide. What a nightmare.

And the National Weather Service agrees. The post-storm assessment of Hurricane Isabel in 2003 found that “WFOs should highlight any Storm Tide forecasts in their tropical cyclone products and emphasize the total height of water expected” because emergency managers, media, and storm drainage personnel found it “more effective”. In other words, quit mixing the way the storm-surge forecast is communicated and stick with the worst case water-rise number. Also, quit hiding the information at the bottom of obscure bulletins and advisories. But, somehow, none of that got adopted.

The Mount Holly National Weather Service, serving the Jersey Shore (up to Sandy Hook just south of New York City), had stronger language in its Coastal Flood Watch and a somewhat better forecast early that Saturday morning:

…MODERATE TO MAJOR COASTAL FLOODING IS ANTICIPATED FOR BOTH HIGH TIDE CYCLES ON MONDAY…

And buried in the RAINFALL text:

…RIVERS WILL NOT BE ABLE TO DISCHARGE EXCESS RUNOFF INTO THE 3 TO 5 FOOT TIDAL SURGE AIDED BY AN INCOMING WIND GUSTING TO 60 MPH… SANDY HOOK MAY SEE A COASTAL FLOOD OF RECORD MONDAY EVENING IF THE STORM CROSSES THE COAST SOUTH OF SANDY HOOK NEAR THE TIME OF THE MONDAY EVENING HIGH TIDE…

Bizarrely, the storm-surge forecast ONLY shows up in the RAINFALL section of the Coastal Flood Watch bulletin. Talk about hiding the most important information!

The bottom line: Upton forecast 2 to 3 feet (and was communicating with the New York City officials), which was well less than Irene, and Mt. Holly forecast 3 to 5 feet. Sandy produced a storm surge of 9 to 10 feet. Clearly there was bad computer guidance, bad analysis, or bad something because the forecast track, strength, and size of the storm were essentially correct. And they are the key parameters used in to forecast storm surge.

This was a colossal failure of the U.S. forecasting system and should be first on the list of issues to be examined.

Saturday Afternoon

The National Hurricane Center issued its first storm-surge forecast for the Northeast Saturday at 11:00 AM: 4 to 8 feet for the New York City area. The top end of that range ended up being more than a foot too low, but this estimate was drastically better than the forecasts from the local offices issued that morning. And, a potential 8-foot surge forecast should have gotten every emergency planner’s attention… although the forecast for Irene was also 4 to 8 feet, which was a point of confusion. In retrospect, an NHC forecast of 4 to 9 feet would have been a more impactful, just to highlight the difference from Irene.

In any case… voila, the Upton office increased its forecast and intensified its wording almost three hours later. (Why did it take that long?) The headline in the Coastal Flood Watch issued at 1:39 PM was:

...MODERATE TO MAJOR COASTAL FLOODING LIKELY MONDAY MORNING INTO TUESDAY MORNING...

And the body of the text included:

…THE POTENTIAL IS INCREASING FOR A MAJOR COASTAL FLOODING EVENT WITH POSSIBLE DAMAGE IN HISTORICALLY FLOOD PRONE SPOTS.

They should NOT have included the word “moderate” in the headline, and most of the homes that went under water would not have been considered to be “historically flood prone”, but they were moving in the right direction. When the Watch was upgraded to a Warning late in the afternoon, they continue with the same wording.

Unfortunately, when Mt. Holly upgraded to a Warning for the Jersey Shore at 5:08 PM, they quit forecasting storm surge numbers altogether and switched exclusively to the height above MLLW. And, they did NOT adopt the higher NHC forecast! Mt. Holly forecast 9.0 to 9.5 feet above MLLW for Monday morning at Sandy Hook, NJ (which is LOWER than Irene’s peak) and 8.0 feet for Monday evening (much lower than Irene). Strange but true. The final height above MLLW during the worst of Sandy that Monday evening was at least 13.5 feet.

So Mt. Holly had a terrible forecast AND a bad communications policy AND ignored the superior numbers issued by the National Hurricane Center. A triple-colossal systemic failure.

It is true that people along the Jersey Shore who are used to looking at tide gauges understand the “above-MLLW” numbers. But it’s inexplicable and inexcusable that an average person needs a Master’s Degree in Storm Surge to decipher public warnings for a life-threatening event like Sandy. Not to mention the terrible forecasts.

You might think… surely they put information in the bulletin explaining how to convert from the MLLW numbers in the new forecast to the storm surge numbers in their previous forecasts (in this area subtract about 4 to 5 feet). Nope. Surely has left the building.

The NHC Storm Surge Forecast

The National Hurricane Center increased their storm-surge forecast at 11:00 PM Saturday night for Long Island Sound (north of NYC) and Raritan Bay (south of NYC) to 5 to 10 feet. New York Harbor stayed at 4 to 8 feet. At 8:00 AM Sunday they upped the forecast to 6 to 11 for the entire New York City area.

The NHC used this sentence to describe its storm-surge numbers:

THE WATER COULD REACH THE FOLLOWING DEPTHS ABOVE GROUND IF THE PEAK SURGE OCCURS AT THE TIME OF HIGH TIDE...

I’m not crazy about the “above ground” reference, but I get the point. They are trying to relate the surge to something people can understand. The problem is that anybody living near the water immediately asks, “Do you mean above the ground in front of my house?” The answer is almost always “no”, of course, and you eventually come around to explaining that the storm-surge forecast is how much above normal the ocean water is expected to be pushed by to the storm. It would be good if the statement were revised to eliminate the obvious above-which-ground confusion. But, that’s a quibble.

The fact is, the people that know how to forecast storm surge are at the National Hurricane Center in Miami. There is a whole unit there that lives with the challenges of storm surge forecasting and communicating every day. There may be excellent weather forecasters at the local National Weather Service offices, but they can’t be expected to be storm-surge experts and tornado experts and every-other-kind-of-weather experts.

The confirmed-and-then-retracted report from the NOAA Hurricane Meeting this month says that the NHC’s much-delayed Storm Surge Warning program will go into internal-experimental mode this year, with public release in 2015. How the Storm Surge Warning would have been implemented in non-hurricane-warned Hurricane Sandy is an open question. But, we can only hope that this will be a first step toward improving storm surge forecasts and standardizing communications from local National Weather Service offices as well.

The National Hurricane Center exists because hurricanes are a specialized slice of meteorology. The local offices are wasting their time trying to forecast storm surge in parallel with the NHC, and there are other things, like communicating, they should be doing better. There is a systemic change required here that only the National Weather Service Headquarters in Washington can implement, and it needs to be done right away.

In addition to adding a Storm Surge Warning, the NHC needs to change their surge-forecasting timetable to reflect the reality on the ground in a mega event like Sandy. The first surge forecasts are currently released two days before landfall, normally coincident with the Hurricane Watch. That will work in most cases, but not an extreme event. As we have seen, critical decisions were required in New York City on Friday, the day before the NHC issued its first storm-surge numbers for that area. The key message, “the surge threat for New York from Sandy is significantly greater than it was in Irene” was needed THAT day to clear away the comparative confusion that was hindering decision makers. Plainly we need new and clear storm-surge messaging for use three and four days in advance of the storm’s landfall in situations like Sandy.

Surge Forecasts from Local NWS Offices on Sunday

The Upton, NY National Weather Service office, which serves the area in and around New York City, increased their storm surge forecasts in step with the National Hurricane Center, sort of. Here’s their wording at 8:00 AM Sunday morning:

…POTENTIAL FOR 5 TO 10 FT ABOVE MONDAY NIGHT INTO TUESDAY MORNING. THE HIGHER END OF THE RANGE RELEGATED TO THE MOST FLOOD PRONE COASTAL LOCATIONS WHERE TIDAL DEPARTURES WILL REACH 6 TO 11 FT. THIS INCLUDES WESTERN LONG ISLAND SOUND.

What does that mean? How is 6 to 11 at the higher end of 5 to 10? At that time the NHC was forecasting 6 to 11 feet ALL around New York City, including New York Harbor, so why hedge the numbers? You get the feeling that Upton didn't fully buy into the NHC forecast.

In the same bulletin, Upton issued a specific forecast of 8.4 feet above MLLW (remember, subtract 4 to 5 feet to get the surge). First, issuing a storm surge forecast to the tenth of a foot is a terrible idea. Why don’t we issue temperature forecasts as 75.4 degrees? Obviously, because it’s bad science. Storm surge can't be forecast with that kind of precision.

But also, that forecast is for Monday MORNING. It’s a confoundingly confusing combination of numbers and formats and time periods. I know it doesn't seem so confusing to people that use these bulletins every day, but people in the media and decision makers in city and state government are NOT in that category. Numbers stand out… that’s where your eye goes. And confusing numbers make a confusing message.

Mt. Holly increased its forecast numbers as well, but at a slower rate. It wasn't until 4:41 PM on Sunday afternoon, just over a day before landfall, that they finally issued a forecast representative of the actual storm surge that occurred. Though their numbers on Sunday morning would have raised alarm in any decision maker who had the decoder ring for the above-MLLW forecasts.

The Hurricane Isabel report had the answer. Let’s get storm surge forecasts standardized and in a format that everybody can understand.

Don’t Forget the Rivers

That 6 to 11 foot NHC storm-surge forecast for New York Harbor had ramifications beyond the immediate coastline. As the harbor filled, water pushed up the Hudson River raising the water level in Newark Bay and pushing water up the Passaic and Hackensack Rivers… with devastating results. You may have seen the damage in Little Ferry and Moonachie, which are south of Hackensack in Bergen County, NJ. Water poured through homes blocks from the river.

The problem is, nobody told those people the water was coming.

The Upton NWS office, which is responsible for that area, included a broad statement in their Sunday afternoon Coastal Flood Warning. The affected area included:

…THE TIDALLY AFFECTED PORTIONS OF THE HACKENSACK AND PASSAIC RIVERS…

But, they did NOT include Bergen County in the list of counties that were warned. No county listed meant no warning on NOAA weather radio, cable systems, and the like. Yet another systemic failure.

Confusing the Decision Makers?

When a plane crashes these days, it’s usually a chain reaction of all the wrong things – somebody spills his coffee, so somebody doesn't notice a gauge, then this then that. If just one person had done something different, the day could have been saved. The Sandy communications and forecasting fiasco was a similar cascade of missed opportunities.

If the folks at the Upton NWS office really understood the threat, why didn't they speak up when the health commissioners and the Mayor were headed in the wrong direction on Friday and Saturday? Somebody should have said, “Yo, Mayor, you’re going to look like an idiot if you don’t get with the program”.

The thing is… Upton’s bulletins and statements indicate that they didn't understand the threat. But where was the rest of the National Weather Service? And are those New York City people in such a hardened bubble that the extreme alerts that were on The Weather Channel and in the New York Times didn't penetrate at all? Governor Christi and mayors up and down the coast got the message. There is clearly something wrong at New York City emergency management that confusion was allowed to rule the day.

Standard operating procedure in an extreme situation should be to plan on the WORST credible level of threat, not the best-case scenario. New York City didn't follow that rule. Bad on them.

But in the series of blown forecasts and systemic failures, the National Weather Service’s decision to NOT issue a Hurricane Watch and Warning had a nasty side effect that might have played into the problem as well. No Hurricane Local Statements were issued by the local NWS offices because Sandy was forecast to morph into a nor'easter right before landfall (a policy that hopefully will never be used again). The Hurricane Local Statement is an annoyingly long synopsis of the threats to the local area, but without it the local message is fragmented in little known and, as we've seen, arcane bulletins in a variety of technocratic formats. This is bad communications plan at any time, let alone leading up to a historic disaster.

Had the Hurricane Watch been issued on Saturday, Hurricane Local Statements would have come out summarizing the local threats. Even though that would have been late in the city’s decision-making process, would it have made a difference? You never know, but it couldn't have hurt. And, sometimes it only takes one person to notice that something’s not right to stop a cascade of bad decisions.

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18. ChrisH57
7:41 PM GMT on January 02, 2013
Quoting V26R:
Chris
If you are going on what that map of yours says
Its wrong all around
All of Staten Island would not have gotten flooded
as well as you are missing the entire Jamaica Bay Basin
I don't know what happened in Manhattan as I was working in Southwestern Brooklyn But I do know that
the entire JB Basin did flood over as well as the
coastal areas of Staten Island
Another problem with your map is that the majority
of people who lived in those flood prone areas on your map either did not know about it or did not have access to it (Since your from Texas, I'll hold my jokes) Go out and ask any farmer who lives near any major river in Texas if they know what the flood risk plan is. I'll bet they do not, then go ask them is they know how to find it! again, nope!
Like (I think Bryan) said if one person would have received any type of warning from the Bloombag administration, maybe it would have set something in motion where the damage would have occured, but the Injuries and Deaths would have not
Maybe something good will come out of this thing
(I hope!)


Note - the map isn't mine, it was issued by the Coastal Emergency Risk Assessment (CERA).
Member Since: December 18, 2012 Posts: 0 Comments: 2
17. WunderAlertBot (Admin)
2:21 PM GMT on January 02, 2013
bnorcross has created a new entry.
16. V26R
6:44 PM GMT on December 23, 2012
#5
I don't think Bloombag was the one making the decisions on this. SOmeone had his ear and was giving
him alot of bad Intel on this system, and like a good politician, he took the advise that he thought was correct. I remember s statement from the book
Red Storm Rising, when Jack Ryan was talking to The
Chief of Staff and The COS says Hey Im just a Politican and that means that when Im not kissing babies to make myself look good Im actually stealing their candy to cover my ass. Bloombag is that type of politician and just choose the wrong person to listen
to with this situation. I really would love to know who was feeding him the intel on this and hang them
in Times Square
Member Since: July 20, 2006 Posts: 0 Comments: 1762
15. V26R
6:38 PM GMT on December 23, 2012
Bap
thats just called emphasising a word or a statement
to get your point across
AND Im going to leave it at that
Member Since: July 20, 2006 Posts: 0 Comments: 1762
14. bappit
8:11 AM GMT on December 22, 2012
Quoting V26R:
Hey Bap
What do you mean Rant?
This sounds like an intelligent conversation to me
Am I missing something?

I'll just pick a sentence.

"So Mt. Holly had a terrible forecast AND a bad communications policy AND ignored the superior numbers issued by the National Hurricane Center. A triple-colossal systemic failure."

Anytime you have words in all caps ("AND") or use of the words "terrible" and "colossal" you are probably looking at a rant. The tone of the entire blog post is similar to this one sentence. Ergo, it is a rant. I'll grant you that it has more details than a previous rant on the subject--it is a pretty good rant--but it is still a rant.
Member Since: May 18, 2006 Posts: 10 Comments: 5960
13. Number5MoreInput
2:27 AM GMT on December 22, 2012
Friday afternoon:
[Bloomberg said] a firm decision would be made Sunday about whether public schools will be open Monday. “Everybody should plan to go to school and plan to go to work,” he added.

“There are some forecasts that say it’s going to weaken. Some forecasts say it’s going to strengthen. Some forecasts say it’s going to hit south of us or north of us or on us. Nobody really knows.”

He's confused by disagreeing forecasts, and doesn't yet understand that it's so big it doesn't really matter exactly where it hits.

Saturday afternoon:
“Let me tell you first we are not ordering any evacuations as of this time for any parts of the city. We’re making that decision based on the nature of the storm.

“Although we’re expecting a large surge of water, it is not expected to be a tropical storm or hurricane-type surge. With this storm, we’ll likely see a slow pileup of water rather than a sudden surge, which is what you would expect with a hurricane, and which we saw with Irene 14 months ago.

“So it will be less dangerous."

Very clear that Bloomberg for one *was* making decisions based on whether it was a "hurricane."

As for me, I must say I am ***EXTREMELY GRATEFUL*** to the weather bloggers, because without them I wouldn't have known. I normally read the NHC website and the local NWS forecasts. I was very lucky to discover weather bloggers around the time of the Joplin tornado. (I'm not a weather hobbyist, just a rubbernecker. :/ )

Both the NHC forecasts and the local NWS forecasts were less severe than the weather bloggers' statements. *Especially* the local NWS forecasts. The NHC forecasts, you could interpret as just middle-balling it while the weather bloggers were warning of the worst case scenario. The locals though...almost managed to convince me the NHC and weather bloggers were overhyping the situation. Luckily, I believe in preparing for the worst case scenario!

As for "smart people," all I can say is I'm a member of SET. That's a study run by JHU: SET members scored above the 98th percentile on the SAT before age 13, and since the SAT is normally taken by 17-year-olds, JHU estimates that such a score at under 13 puts us in the top 1 in 10,000 in general intelligence. Granted I have no common sense, as illustrated by the fact that I'm willing to post this to a bunch of strangers on the internet. ;) But still...like I said...

If it weren't for the weather bloggers, looking just at the local NWS forecasts and even the NHC, I wouldn't have known.
Member Since: December 22, 2012 Posts: 0 Comments: 0
12. V26R
3:24 AM GMT on December 21, 2012
Hey Bap
What do you mean Rant?
This sounds like an intelligent conversation to me
Am I missing something?
Member Since: July 20, 2006 Posts: 0 Comments: 1762
11. V26R
3:21 AM GMT on December 21, 2012
Chris
If you are going on what that map of yours says
Its wrong all around
All of Staten Island would not have gotten flooded
as well as you are missing the entire Jamaica Bay Basin
I don't know what happened in Manhattan as I was working in Southwestern Brooklyn But I do know that
the entire JB Basin did flood over as well as the
coastal areas of Staten Island
Another problem with your map is that the majority
of people who lived in those flood prone areas on your map either did not know about it or did not have access to it (Since your from Texas, I'll hold my jokes) Go out and ask any farmer who lives near any major river in Texas if they know what the flood risk plan is. I'll bet they do not, then go ask them is they know how to find it! again, nope!
Like (I think Bryan) said if one person would have received any type of warning from the Bloombag administration, maybe it would have set something in motion where the damage would have occured, but the Injuries and Deaths would have not
Maybe something good will come out of this thing
(I hope!)
Member Since: July 20, 2006 Posts: 0 Comments: 1762
10. bappit
6:17 PM GMT on December 20, 2012
This is a better rant than the previous one on this topic.
Member Since: May 18, 2006 Posts: 10 Comments: 5960
9. ChrisH57
2:04 PM GMT on December 19, 2012
Quoting bnorcross:
Chris,

My understanding is that the NHC forecast is supposed to convey the highest the water level can get including all of the surge factors you list. So their forecast of 6 to 11 feet meant that they expected the water to be 6 to 11 feet above the ground if you were standing at the water's edge at high tide. Then, of course, waves would be on top of that.

In the end the water came up 9.23 feet. The difference between MLLW and the surge is about 4.7 feet at the Battery.

Just the fact that we keep talking about the definitions is an indication of how important it is to have one standard way of talking about storm surge.

Thanks.



Bryan,

I'm not aware that NHC surge forecasts include the astronomical tide. The reason for that is the uncertainty as to the timing of landfall. Did you check with the NHC to see if they include tides in the surge forecasts? I don't think they do.

Are you going to attend the AMS meeting in Austin in a few weeks? Should be a lively Sandy town hall meeting on Monday evening.

I think one big problem is that we cannot use words alone to convey the surge threat. The public need graphics. Unfortunately, the NHC stopped producing detailed surge graphics this year in favor of those low-resolution probabilistic surge graphics. The public don't want to know that there is a 40% chance of a 10ft surge, they want to know "what does it mean to me?"

The maps produced by the Coastal Emergency Risk Assessment (CERA) website prior to Sandy's landfall were a great tool for conveying the real threat from Sandy, but they never got much attention. Check out the image below, released a day or two prior to Sandy's arrival. It shows southern and western Long Island underwater and Staten Island completely underwater. That would get the public's attention:

CERA Sandy Graphic
Member Since: December 18, 2012 Posts: 0 Comments: 2
8. Wista
11:29 AM GMT on December 19, 2012
Speaking of bad decisions made by local agencies, one of the worst was made by NJ transit. They moved most of their rolling stock to a flood area

Link

Member Since: December 6, 2012 Posts: 0 Comments: 6
7. Bryan Norcross , Hurricane Specialist
2:49 AM GMT on December 19, 2012
Chris,

My understanding is that the NHC forecast is supposed to convey the highest the water level can get including all of the surge factors you list. So their forecast of 6 to 11 feet meant that they expected the water to be 6 to 11 feet above the ground if you were standing at the water's edge at high tide. Then, of course, waves would be on top of that.

In the end the water came up 9.23 feet. The difference between MLLW and the surge is about 4.7 feet at the Battery.

Just the fact that we keep talking about the definitions is an indication of how important it is to have one standard way of talking about storm surge.

Thanks.

Member Since: August 24, 2012 Posts: 38 Comments: 8
6. Patrap
12:56 AM GMT on December 19, 2012
Here's the graphic from the MDL website for Sandy's impact at The Battery. The red dashed line is the total water height above MLLW for Sandy's passage

















Member Since: July 3, 2005 Posts: 421 Comments: 127636
5. ChrisH57
9:28 PM GMT on December 18, 2012
Bryan,

I share your concerns about the poor communication about the threat Sandy posed to the northeast. I'm a hurricane forecaster working for a private weather company in Houston, TX. Reading through your post, I noticed a few things.

The term "MLLW" (Mean Lower Low Water) is the standard datum from which all tides are measured, both high and low. A predicted high tide of 8ft, for example, means that the water will reach 8ft above MLLW.

As for the tides associated with Sandy's landfall, there is more confusion. First, there were the astronomical tides, which were quite high due to the full moon. Then there was the setup tide, a water level increase due to large waves moving into the coast. Finally, there was the storm surge, a mound of water that moves ashore just ahead of the center of the storm. All three of these put together equal the "storm tide". I believe that the value reached at Battery Park, for example, was around just under 14ft (13.88ft above MLLW to be exact). Of that 13.8ft, about 5 feet was due to the normal astronomical tide. The actual storm surge was closer to about 8-9ft at The Battery.

Some excellent graphics can be found at the Meteorological Development Lab's website , but they clearly showed the components of Sandy's storm tide, including the height of Sandy's storm surge alone.

Here's the graphic from the MDL website for Sandy's impact at The Battery. The red dashed line is the total water height above MLLW for Sandy's passage:



Normally, when a tropical cyclone is making landfall, a forecast is made of the storm surge height alone, not to include any astronomical tides. This means that the public need to understand their elevation and be able to calculate whether or not an additional, say, 8ft of water is going to inundate their homes. The NHC is making an attempt at communicating that the water may reach a particular height "above ground", but this is not very easy considering that even a small section of the coast will have quite significant differences in elevation.

Trying to communicate how high the water might rise above ground is going to be impossible using words alone. What is needed is a highly-detailed graphical representation of potential storm surge. I'm aware of the probabilistic storm surge graphics generated by the NHC and I'm definitely not a fan. They're about as clear as mud for the general public. Sandy demonstrated once again for better communication on potential storm impact.

Member Since: December 18, 2012 Posts: 0 Comments: 2
4. terstorm
8:05 PM GMT on December 18, 2012
I found this in the Hurricane Irene Service Assessment:

Finding 18: The reliance of NWS on a single person at the SSU for internal and external storm surge decision support led to extreme fatigue and is not sustainable. This is a potential single point of failure.

Recommendation 18 (Strategic): An additional federal employee should be allocated to the SSU. The NWS should establish a 24-hour SSU tropical cyclone support and Technical Support Branch capability with staff members who can provide official guidance and support to field offices, ROCs, and external partners during a threat for a landfalling tropical cyclone.


Would anyone know if this was done?
Member Since: October 11, 2005 Posts: 0 Comments: 27
3. Bryan Norcross , Hurricane Specialist
3:17 AM GMT on December 18, 2012
I agree that media and emergency management people should all be able to decode all of this and immediately know what's really bad. And I think most EMs can. But, remember, the surge forecasts from Upton and Mt. Holly were terrible Friday and Saturday. The actual numbers were bad.

I also agree that Mt. Holly writes excellent discussions and is generally on of the best NWS offices. That makes it doubly surprising that they would put out such bad numbers... even forgetting the format.

The good news is, their numbers were just high enough to scare the state officials into ordering the evacuation on Saturday... but the lower numbers out of Upton were low enough to convince NYC officials that the no-evacuation decision was the right one.

Sandy Hook is the top of Mt. Holly's area.
Member Since: August 24, 2012 Posts: 38 Comments: 8
2. terstorm
7:50 PM GMT on December 17, 2012
I thought Sandy Hook was in Upton's forecast region?

(Mt. Holly's forecasts were very dire for several days, even if that doesn't seem reflected in the various products the offices put out. To be honest, when I logged on to Mt. Holly's page before the storm I only read the briefings at the top of the page which were very alarming. Also, can all forecast offices write their technical discussions like Mt. Holly does?)

It does seem that some of the messaging did contribute to bad decisions in New York City, even though the media was screaming its head off. I think this will get addressed in the service assessment.

Member Since: October 11, 2005 Posts: 0 Comments: 27
1. Wista
5:29 PM GMT on December 17, 2012
I know it doesn't seem so confusing to people that use these bulletins every day, but people in the media and decision makers in city and state government are NOT in that category

The emergency management staff in cities (certainly in a major city such as NYC) should very well know what these numbers mean. And certainly the weather forecasters in media outlets should know. I still think the warnings were extremely clear several days before the storm -- a very major, very dangerous storm was on the way. About Little Ferry and Moonachie: there is flooding in the cities even with relatively minor storms. The whole cities are in flood plains. Also, I realize that the inhabitants of nursing homes are often old and infirm, but 48 hours being required for evacuation strikes me as excessive. And Mount Holly's warnings were as dire as can be. Of course, there were residents who ignored Katrina warnings too.


I think the real issue is that Irene's impact in some areas (including NYC) was less than anticipated, so planners and residents in those areas were less likely to take action. Those impacted by Irene took much better precautions this time around.

Ultimately, there is always going to be uncertainty in weather forecasting. The key problem is getting people to take attention, while recognizing the danger of crying wolf.


Member Since: December 6, 2012 Posts: 0 Comments: 6

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This is the official blog for Bryan Norcross, Hurricane Specialist at The Weather Channel.

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