Lessons from Isaac: Communicating the hurricane hazard

[BeauDodson]

http://isaaclessons.blogspot.com/?view=classic

Snip....

The Rain and Category Bias: A major concern for me is that media and public familiarity with the Saffir-Simpson (SS) scale leads to underestimation of the most deadly threat of a hurricane, inland freshwater flooding. It is very common to see a reporter on the beach in the wind, struggling to stand. It is also common to focus on what the SS category of the storm is and when it will become a hurricane or a “category 3” storm. A gentleman from Plaquemines Parish, discussing a levee breach and severe flooding in the Parish said, “we didn’t leave because they were saying it was not going to be a Katrina, but we wish we did”. This illustrates, in my view, an over dependence on assuming threats are only associated with major hurricanes. In fact, our own studies have shown that weaker storms can be significant rain-flood producers. With Isaac, the storm was also very large in area and moving very slowly. This combination led to localized rainfall totals in the 20 to 30 inch range. The “water” from rainfall and flooding is just as significant as the wind and surge. Is it time to consider an augmentation of the Saffir Simpson scale to capture the rainfall-flood threat? It is a difficult science problem, but probably one worth investigating. I also argue that our media colleagues must consider their coverage strategy and category “anticipation” or hype carefully.

[usedtobe]

http://isaaclessons....m/?view=classic

Snip....

The Rain and Category Bias: A major concern for me is that media and public familiarity with the Saffir-Simpson (SS) scale leads to underestimation of the most deadly threat of a hurricane, inland freshwater flooding. It is very common to see a reporter on the beach in the wind, struggling to stand. It is also common to focus on what the SS category of the storm is and when it will become a hurricane or a “category 3” storm. A gentleman from Plaquemines Parish, discussing a levee breach and severe flooding in the Parish said, “we didn’t leave because they were saying it was not going to be a Katrina, but we wish we did”. This illustrates, in my view, an over dependence on assuming threats are only associated with major hurricanes. In fact, our own studies have shown that weaker storms can be significant rain-flood producers. With Isaac, the storm was also very large in area and moving very slowly. This combination led to localized rainfall totals in the 20 to 30 inch range. The “water” from rainfall and flooding is just as significant as the wind and surge. Is it time to consider an augmentation of the Saffir Simpson scale to capture the rainfall-flood threat? It is a difficult science problem, but probably one worth investigating. I also argue that our media colleagues must consider their coverage strategy and category “anticipation” or hype carefully.

Beau, I agree to an extent. There needs to be a better way to communicate the threat as many people actually look for excuses for why not to act so if your statement gives one incidation that the storm won't be that bad (a cat 1 storm for example) they may not pay attention to the details specifying that the real threat is the slow movement. Also, don't always listen well. The forecasts always mentioned that with this storm because of it's slow movement and size would be a signficant rainfall and surge producer which could be a major problem. Instead of hearing the entire message, gentleman you site may have only heard or heeded the part that noted that the storm was only going to be a cat 1. In this case, the Plaquemines parish people were told that there would be 9-12 surge if I'm not mistaken while the parish was only protected by an 8 foot levee. That should have been conveyed clearly in a local statement. somehow threats other than the objective wind criteria probably need to be built into any objective rating scheme. However, devising such a scheme is not a trivial exercise. some fo the very heaviest rainfall have been decaying systems that no longer even are worthy of being called tropical depressions. I'm not sure how you could objectively handle such systems as their impact can be huge but over a fairly small geographic area. Amelia in 1978 (48 inches) and Allison in 2001 (40.6 inches) are two examples where there was extreme rainfall from a tropical system over a fairly small area.

Another problem is that the media pretty much hypes all storms that are going to impact the u.s which can lead to people not listening when the next more significant storm in on the way.

[HurricaneJosh]

The advisories *explicitly* warned of the great surge and rainfall threats, even in the opening sentences. If people are so dense that they're not going to listen to explicit, plain English, I'm not sure that some fancy new scale that warns of "Cat-5 rainfall" is going to help them. The NHC explicitly and adequately warned people about this storm.

[eyewall]

Lesson: When you live a foot above sea level in a swamp it will flood when a hurricane comes.

[HurricaneJosh]

Lesson: When you live a foot above sea level in a swamp it will flood when a hurricane comes.

Bingo. I'm surprised that anyone in that region-- which is so vulnerable and has been hit so many times in recent years-- would be surprised.

By the way, the average townspeople I met on my chase struck me as the opposite-- they seemed extremely knowledgeable and conversant Re: the mechanics and threats of a hurricane. In fact, I would say these Louisiana bayou people are the most knowledgeable natives I've met on any chase, anywhere.

[gymengineer]

I've been throwing out or agreeing with ideas in the other thread about the SS scale.... Please understand these are just brainstorms. I'm not tied to any of them-- just running thought experiments. So, if you think an idea I mention is idiotic, please just reply gently and understand I'm not assuming it would work better than what's available.

So, one idea was to include the IKE in any public forecast. Another idea was to have a 3-indicator scale (wind/storm surge/rain). Another was to just completely eliminate the SS scale mention from any public advisory, instead saving those only for technical discussions, post-storm reports, etc. So, any forecast advisory would just simply state that the storm is a hurricane.

Here's another idea for changing the communication of threats: What if the entire warning system were revamped? No more tropical storm or hurricane warnings to cover all the coastal hazards (since you can have tropical storm force winds accompanied by a 12 foot storm surge). Instead, there would be a separate wind and surge warnings (the local offices already cover the inland flooding). Wind warnings would be: Gale force, Storm force, Hurricane force. Storm surge warnings might be something like: Coastal Flood, Strong Coastal Flood, Severe Coastal Flood. So, for example, for a large tropical storm in the Gulf headed towards Gulfport, the warnings issued might be: 1) Storm force winds warning; 2) Severe coastal flood warning.

[HurricaneJosh]

Gymengineer, I feel like breaking up the storm description into component parts like that is taking a step backward, because at the end of the day, the word "hurricane" is a terrifically efficient word that means "severe cyclone with destructive winds, heavy rain, and storm surges that will become more severe the closer you are to the center, and that will cause a short-lived lull in your area if the center passes over your location". For an attention-challenged audience, I think you want to keep it simple, and the word "hurricane" is a simple and efficient way to convey a lot of information.

This aside, I think the wind scale is important. Most people do want to have a basic idea if what's coming their way is an Irene or a Charley. Yeah, storm surge kills more people, but more people are affected by the wind, and they want to know if we're talking tree damage or their houses being mowed down.

At the end of the day, it seems like we're trying to fix somethin' that ain't broke. I don't see how it makes sense to completely scrap a good warning system because 1 out of 1,000 people is just so completely dense that they don't understand that a swamp a foot above sea level floods in a tropical storm.

[gymengineer]

Gymengineer, I feel like breaking up the storm description into component parts like that is taking a step backward, because at the end of the day, the word "hurricane" is a terrifically efficient word that means "severe cyclone with destructive winds, heavy rain, and storm surges that will become more severe the closer you are to the center, and that will cause a short-lived lull in your area if the center passes over your location". For an attention-challenged audience, I think you want to keep it simple, and the word "hurricane" is a simple and efficient way to convey a lot of information.

This aside, I think the wind scale is important. Most people do want to have a basic idea if what's coming their way is an Irene or a Charley. Yeah, storm surge kills more people, but more people are affected by the wind, and they want to know if we're talking tree damage or their houses being mowed down.

At the end of the day, it seems like we're trying to fix somethin' that ain't broke. I don't see how it makes sense to completely scrap a good warning system because 1 out of 1,000 people is just so completely dense that they don't understand that a swamp a foot above sea level floods in a tropical storm.

I would guess there would be disagreement on whether the current warning structure is working very well or not... I'm curious whether Isaac will have an NWS Service Assessment conducted, and if so, what the recommendations are that follow. For example, a lot of people argued that the system was fine for tornado warnings in light of the April '11 and Joplin tornadoes, and that the public was who bore all the responsibility for the large number of deaths. The NWS assessment team disagreed that the system was fine as it was and issued recommendations specifically regarding the phrasing of warnings, inviting in social scientists to study what would better motivate the public to act, etc.

Also, although more people are affected by wind than storm surge, way more people are affected by heavy rains through the entire life of the storm than by strong winds. Right now, the inland flooding task is left to the local forecast offices and HPC. So, again, why is the wind scale the only scale that is put forward for public consumption by the NHC?

[HurricaneJosh]

I would guess there would be disagreement on whether the current warning structure is working very well or not... I'm curious whether Isaac will have an NWS Service Assessment conducted, and if so, what the recommendations are that follow. For example, a lot of people argued that the system was fine for tornado warnings in light of the April '11 and Joplin tornadoes, and that the public was who bore all the responsibility for the large number of deaths. The NWS assessment team disagreed that the system was fine as it was and issued recommendations specifically regarding the phrasing of warnings, inviting in social scientists to study what would better motivate the public to act, etc.

Joplin was the deadliest single tornado in the better part of a century. How many people died in Isaac? One? If we're going to judge warnings by number of fatalities, Isaac was a terrific success.

Louisiana was prepared. On the ground in the bayous, I saw firsthand that people were well-warned and getting ready more than 24 hr in advance. On the governmental level, state, parish, and city authorities were all over this and well-prepared-- not just New Orleans but smaller towns as well. No one was caught off guard by this storm. Again, if you live in Plaquemines Parish and you're surprised about tropical cyclone flooding, a psychiatrist might be more helpful than a new warning system.

Also, although more people are affected by wind than storm surge, way more people are affected by heavy rains through the entire life of the storm than by strong winds. Right now, the inland flooding task is left to the local forecast offices and HPC. So, again, why is the wind scale the only scale that is put forward for public consumption by the NHC?

Because wind speed is the criterion for classing a system as a hurricane-- not the amount of rain it drops. A depression or a tropical wave can dump ten times more rain than a hurricane-- there is no relationship between the word "hurricane" and the amount of rain a system drops. If there were, we'd be calling everything a hurricane.

If an Andrew or a Charley is coming my way, that "Category 5" or "Category 4" designation is going to get my attention and make me appropriately scared.

[turtlehurricane]

I suppose current day NHC public advisories already cover wind, rain, tornadoes, surge, and surf with specific details, so another scale is unnecessary as long as people read the public advisories or the news disseminates it correctly.

TTAA00 KNHC DDHHMM

BULLETIN

TROPICAL STORM ISAAC INTERMEDIATE ADVISORY NUMBER 21A

NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012

800 AM EDT SUN AUG 26 2012

...ISAAC EXPECTED TO BE NEAR THE FLORIDA KEYS LATER TODAY...

SUMMARY OF 800 AM EDT...1200 UTC...INFORMATION

----------------------------------------------

LOCATION...23.5N 80.0W

ABOUT 135 MI...220 KM ESE OF KEY WEST FLORIDA

ABOUT 155 MI...245 KM E OF HAVANA CUBA

MAXIMUM SUSTAINED WINDS...65 MPH...100 KM/H

PRESENT MOVEMENT...WNW OR 300 DEGREES AT 20 MPH...31 KM/H

MINIMUM CENTRAL PRESSURE...995 MB...29.38 INCHES

WATCHES AND WARNINGS

--------------------

CHANGES WITH THIS ADVISORY...

THE GOVERNMENT OF THE BAHAMAS HAS DISCONTINUED THE TROPICAL STORM

WARNING FOR THE CENTRAL AND SOUTHEASTERN BAHAMAS...AND HAS CHANGED

THE HURRICANE WARNING TO A TROPICAL STORM WARNING FOR ANDROS

ISLAND.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A HURRICANE WARNING IS IN EFFECT FOR...

* THE FLORIDA KEYS INCLUDING THE DRY TORTUGAS

* THE WEST COAST OF FLORIDA FROM BONITA BEACH SOUTHWARD TO OCEAN

REEF

* FLORIDA BAY

A HURRICANE WATCH IS IN EFFECT FOR...

* THE FLORIDA EAST COAST FROM GOLDEN BEACH SOUTHWARD TO OCEAN REEF

* THE MOUTH OF THE MISSISSIPPI RIVER TO INDIAN PASS FLORIDA...NOT

INCLUDING METROPOLITAN NEW ORLEANS

A TROPICAL STORM WARNING IS IN EFFECT FOR...

* THE CUBAN PROVINCES OF CIEGO DE AVILA...SANCTI SPIRITUS...VILLA

CLARA...CAMAGUEY...LAS TUNAS...GRANMA...HOLGUIN...SANTIAGO DE

CUBA...AND GUANTANAMO

* THE NORTHWESTERN BAHAMAS

* THE FLORIDA EAST COAST FROM SEBASTIAN INLET SOUTHWARD TO OCEAN

REEF

* LAKE OKEECHOBEE

* THE FLORIDA WEST COAST AND THE FLORIDA PANHANDLE FROM NORTH OF

BONITA BEACH TO INDIAN PASS...INCLUDING TAMPA BAY

A TROPICAL STORM WATCH IS IN EFFECT FOR...

* THE CUBAN PROVINCES OF MATANZAS AND CIENFUEGOS

* THE FLORIDA EAST COAST NORTH OF SEBASTIAN INLET TO FLAGLER BEACH

A HURRICANE WARNING MEANS THAT HURRICANE CONDITIONS ARE EXPECTED

SOMEWHERE WITHIN THE WARNING AREA...IN THIS CASE WITHIN THE NEXT 24

HOURS. PREPARATIONS TO PROTECT LIFE AND PROPERTY SHOULD BE RUSHED

TO COMPLETION.

A HURRICANE WATCH MEANS THAT HURRICANE CONDITIONS ARE POSSIBLE

WITHIN THE WATCH AREA. A WATCH IS TYPICALLY ISSUED 48 HOURS

BEFORE THE ANTICIPATED FIRST OCCURRENCE OF TROPICAL-STORM-FORCE

WINDS...CONDITIONS THAT MAKE OUTSIDE PREPARATIONS DIFFICULT OR

DANGEROUS.

A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE

EXPECTED SOMEWHERE WITHIN THE WARNING AREA WITHIN 36 HOURS.

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE

POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN 48 HOURS.

INTERESTS IN THE REMAINDER OF CUBA...THE REMAINDER OF FLORIDA...AND

THE REMAINDER OF THE NORTHERN GULF COAST SHOULD MONITOR THE PROGRESS

OF ISAAC.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA IN THE UNITED STATES...

INCLUDING POSSIBLE INLAND WATCHES AND WARNINGS...PLEASE MONITOR

PRODUCTS ISSUED BY YOUR LOCAL NATIONAL WEATHER SERVICE FORECAST

OFFICE. FOR STORM INFORMATION SPECIFIC TO YOUR AREA OUTSIDE THE

UNITED STATES...PLEASE MONITOR PRODUCTS ISSUED BY YOUR NATIONAL

METEOROLOGICAL SERVICE.

DISCUSSION AND 48-HOUR OUTLOOK

------------------------------

AT 800 AM EDT...1200 UTC...THE CENTER OF TROPICAL STORM ISAAC WAS

LOCATED NEAR LATITUDE 23.5 NORTH...LONGITUDE 80.0 WEST. ISAAC IS

MOVING TOWARD THE WEST-NORTHWEST NEAR 20 MPH...31 KM/H. A WEST-

NORTHWESTWARD TO NORTHWESTWARD MOTION IS EXPECTED DURING THE NEXT

48 HOURS WITH A GRADUAL DECREASE IN FORWARD SPEED. ON THE FORECAST

TRACK...THE CENTER OF ISAAC IS EXPECTED TO MOVE JUST NORTH OF CUBA

THIS MORNING...MOVE NEAR OR OVER THE FLORIDA KEYS LATER TODAY AND

TONIGHT...AND MOVE INTO THE EASTERN GULF OF MEXICO ON MONDAY.

MAXIMUM SUSTAINED WINDS ARE NEAR 65 MPH...100 KM/H...WITH HIGHER

GUSTS. SOME STRENGTHENING IS FORECAST DURING THE NEXT 48 HOURS...

AND ISAAC IS EXPECTED TO BE AT OR NEAR HURRICANE STRENGTH WHEN IT

REACHES THE FLORIDA KEYS.

TROPICAL-STORM-FORCE WINDS EXTEND OUTWARD UP TO 205 MILES...335 KM

FROM THE CENTER. MOLASSES REEF RECENTLY REPORTED A WIND GUST TO 54

MPH...87 KM/H.

THE LATEST MINIMUM CENTRAL PRESSURE REPORTED BY THE AIRCRAFT WAS 995

MB...29.38 INCHES.

HAZARDS AFFECTING LAND

----------------------

RAINFALL...TOTAL RAINFALL ACCUMULATIONS OF 4 TO 8 INCHES...WITH

MAXIMUM AMOUNTS OF 12 INCHES...ARE POSSIBLE ACROSS THE FLORIDA

KEYS...THE SOUTHERN PENINSULA OF FLORIDA AND PORTIONS OF CENTRAL AND

EASTERN CUBA. TOTAL RAIN ACCUMULATIONS OF 3 TO 6 INCHES ARE

POSSIBLE OVER THE CENTRAL AND SOUTHERN BAHAMAS.

WIND...TROPICAL STORM CONDITIONS ARE OCCURRING OVER PORTIONS OF

EASTERN AND CENTRAL CUBA AND THE BAHAMAS AND THE TURKS AND CAICOS

ISLANDS. TROPICAL STORM CONDITIONS ARE POSSIBLE IN PORTIONS OF

NORTHWESTERN CUBA BY LATE TODAY.

HURRICANE CONDITIONS ARE EXPECTED IN THE HURRICANE WARNING AREA IN

SOUTHWEST FLORIDA AND THE FLORIDA KEYS TODAY. HOWEVER...THE

LIKELIHOOD OF HURRICANE CONDITIONS OCCURRING IN SOUTHEAST FLORIDA

IS DECREASING.

TROPICAL STORM CONDITIONS ARE OCCURRING IN THE TROPICAL

STORM WARNING AREA ALONG THE FLORIDA EAST COAST. TROPICAL STORM

CONDITIONS ARE EXPECTED TO SPREAD NORTHWARD ALONG THE WEST COAST OF

FLORIDA AND INTO THE EASTERN FLORIDA PANHANDLE IN THE TROPICAL

STORM WARNING AREA TONIGHT AND MONDAY.

HURRICANE CONDITIONS ARE POSSIBLE IN THE HURRICANE WATCH AREA ALONG

THE NORTHERN GULF COAST ON TUESDAY...WITH TROPICAL STORM CONDITIONS

POSSIBLE BY MONDAY NIGHT.

STORM SURGE...THE COMBINATION OF A STORM SURGE AND THE TIDE WILL

CAUSE NORMALLY DRY AREAS NEAR THE COAST TO BE FLOODED BY RISING

WATERS. THE WATER COULD REACH THE FOLLOWING DEPTHS ABOVE GROUND IF

THE PEAK SURGE OCCURS AT THE TIME OF HIGH TIDE...

* CRYSTAL RIVER THROUGH THE BIG BEND OF FLORIDA...4 TO 7 FT

* SOUTHWEST FLORIDA COAST WITHIN HURRICANE WARNING AREA...4 TO 6 FT

* FLORIDA WEST COAST FROM BONITA BEACH TO SOUTH OF CRYSTAL RIVER

INCLUDING TAMPA BAY...3 TO 5 FT

* SOUTHEAST FLORIDA COAST AND THE FLORIDA KEYS...1 TO 3 FT

* CENTRAL AND EASTERN CUBA...1 TO 3 FT

* THE BAHAMAS...1 TO 3 FT

THE DEEPEST WATER WILL OCCUR ALONG THE IMMEDIATE COAST IN AREAS OF

ONSHORE FLOW. SURGE-RELATED FLOODING DEPENDS ON THE RELATIVE TIMING

OF THE SURGE AND THE TIDAL CYCLE...AND CAN VARY GREATLY OVER SHORT

DISTANCES. FOR INFORMATION SPECIFIC TO YOUR AREA...PLEASE SEE

PRODUCTS ISSUED BY YOUR LOCAL WEATHER SERVICE OFFICE. NEAR THE

COAST...THE SURGE WILL BE ACCOMPANIED BY DANGEROUS WAVES.

TORNADOES...ISOLATED TORNADOES ARE POSSIBLE OVER PORTIONS OF CENTRAL

AND SOUTHERN FLORIDA AND THE FLORIDA KEYS TODAY.

SURF...DANGEROUS SURF AND RIP CURRENT CONDITIONS WILL CONTINUE TO

AFFECT THE BAHAMAS...THE TURKS AND CAICOS...EASTERN AND CENTRAL

CUBA...THE FLORIDA PENINSULA AND THE FLORIDA KEYS DURING THE NEXT

COUPLE OF DAYS. PLEASE CONSULT PRODUCTS FROM YOUR LOCAL WEATHER

OFFICE FOR MORE INFORMATION.

NEXT ADVISORY

-------------

NEXT COMPLETE ADVISORY...1100 AM EDT.

$$

FORECASTER PASCH/ROBERTS

[HurricaneJosh]

I suppose current day NHC public advisories already cover wind, rain, tornadoes, surge, and surf with specific details, so another scale is unnecessary as long as people read the public advisories or the news disseminates it correctly.

Exactly. They go into great detail about each threat. And I specifically remember the leading statement in the Isaac advisories emphasizing the water threat (surge and rain) without even mentioning the wind. The emphasis was appropriately placed.

[gymengineer]

Joplin was the deadliest single tornado in the better part of a century. How many people died in Isaac? One? If we're going to judge warnings by number of fatalities, Isaac was a terrific success.

Louisiana was prepared. On the ground in the bayous, I saw firsthand that people were well-warned and getting ready more than 24 hr in advance. On the governmental level, state, parish, and city authorities were all over this and well-prepared-- not just New Orleans but smaller towns as well. No one was caught off guard by this storm. Again, if you live in Plaquemines Parish and you're surprised about tropical cyclone flooding, a psychiatrist might be more helpful than a new warning system.

Because wind speed is the criterion for classing a system as a hurricane-- not the amount of rain it drops. A depression or a tropical wave can dump ten times more rain than a hurricane-- there is no relationship between the word "hurricane" and the amount of rain a system drops. If there were, we'd be calling everything a hurricane.

If an Andrew or a Charley is coming my way, that "Category 5" or "Category 4" designation is going to get my attention and make me appropriately scared.

Just the 150 mph sustained wind designation wouldn't do the same? Why is the categorization necessary at that point?

[HurricaneJosh]

Just the 150 mph sustained wind designation wouldn't do the same? Why is the categorization necessary at that point?

For the same reason that broad categories are used to communicate other sets of objects in life-- like the bed size, car size, drink size, etc.: it's easier to remember.

A five-level scale is simple shorthand that quickly communicates a threat and is easy to remember and easier to use when comparing a current threat to previous threats. Residents of Louisiana know that Betsy was a Cat 3 and Gustav was a Cat 2 and that Katrina was a Cat 5 when it was just offshore. I doubt any of them could specifically tell you the exact wind speed in each. An average person can remember five numbers for purposes of comparing different events, whereas remembering that this storm had winds of 105 mph and that one had winds of 125 mph and this one was 80 mph gets more complicated.

[gymengineer]

In other words, the public should be able to interpret the storm surge heights in the forecast without it being assigned a category (interpret meaning comparing it to the height of their location as well as other surges they've experienced), right? So why couldn't they do the same with the wind? So both threats are described in the narrative instead of by a scale...

[gymengineer]

For the same reason that broad categories are used to communicate other sets of objects in life-- like the bed size, car size, drink size, etc.: it's easier to remember.

A five-level scale is simple shorthand that quickly communicates a threat and is easy to remember and easier to use when comparing a current threat to previous threats. Residents of Louisiana know that Betsy was a Cat 3 and Gustav was a Cat 2 and that Katrina was a Cat 5 when it was just offshore. I doubt any of them could specifically tell you the exact wind speed in each. An average person can remember five numbers for purposes of comparing different events, whereas remembering that this storm had winds of 105 mph and that one had winds of 125 mph and this one was 80 mph gets more complicated.

Right.. But that's what people have to do with surges right now.

[HurricaneJosh]

In other words, the public should be able to interpret the storm surge heights in the forecast without it being assigned a category (interpret meaning comparing it to the height of their location as well as other surges they've experienced), right? So why couldn't they do the same with the wind? So both threats are described in the narrative instead of by a scale...

You're comparing apples and oranges.

Surge height is directly relevant to the elevation of your location. If you live 5 ft above sea level, knowing the surge will be 10 ft means you need to leave. Given this, what you need to know immediately is that expected value in ft-- not some broad scale rating.

It does not work this way with wind. No one knows the exact wind speed that is going to tear off their roof. Given this, a broad scale makes sense, since it's simple and easy-to-remember.

[HurricaneJosh]

Right.. But that's what people have to do with surges right now.

See above. A typical resident knows the exact elevation of his town. He does not know what wind speed will tear off his roof.

[HurricaneJosh]

Again, let's go back to Isaac. Why is there a perceived problem with the warnings? Did a lot of people die? Was some area flooded that wasn't expected to be flooded?

[gymengineer]

You're comparing apples and oranges.

Surge height is directly relevant to the elevation of your location. If you live 5 ft above sea level, knowing the surge will be 10 ft means you need to leave. Given this, what you need to know immediately is that expected value in ft-- not some broad scale rating.

It does not work this way with wind. No one knows the exact wind speed that is going to tear off their roof. Given this, a broad scale makes sense, since it's simple and easy-to-remember.

Isaac's surge was higher than Gustav's in most locations and higher than Katrina's in others. You're really saying it would not have helped to have that captured in an easy-to-interpret scale rating on the surge? So just as you are arguing that a Cat 4 SS rating would inspire concern and action, why wouldn't an easy to understand Cat 3 surge rating inspire concern and action as well (even though winds were only Cat 1)?

[gymengineer]

Again, let's go back to Isaac. Why is there a perceived problem with the warnings? Did a lot of people die? Was some area flooded that wasn't expected to be flooded?

There was a couple who died in a house that had water up to the attic. I really don't think officials were expecting that as widespread an area would have greater than Katrina surge as what happened. I mean, overall loss of life was certainly not ridiculous, but many Category 1's don't kill anyone due to surge.

[HurricaneJosh]

Isaac's surge was higher than Gustav's in most locations and higher than Katrina's in others. You're really saying it would not have helped to have that captured in an easy-to-interpret scale rating on the surge? So just as you are arguing that a Cat 4 SS rating would inspire concern and action, why wouldn't an easy to understand Cat 3 surge rating inspire concern and action as well (even though winds were only Cat 1)?

Again, if I know I'm 5 ft above sea level, the single, most-important piece of information for me to know is the expected surge height, in ft-- not a category rating.

It does not work this way with wind-- I don't know the exact wind speed that will cause structural damage to my house.

If Isaac's surge was under-forecast, that is a problem with the forecast, not the style of communication-- i.e., whether the threat was conveyed in ft or a category assignment. Separate issue.

[HurricaneJosh]

There was a couple who died in a house that had water up to the attic. I really don't think officials were expecting that as widespread an area would have greater than Katrina surge as what happened. I mean, overall loss of life was certainly not ridiculous, but many Category 1's don't kill anyone due to surge.

Compared to fatalities in previous hurricanes of all categories, two deaths is low-- especially given the size and duration of the event.

Again, if the surge was under-forecast, that is a problem with the forecast-- not the classification system or the communication style.

[HurricaneJosh]

I just feel the NHC did a very good job with this one, despite the crazy model divergences.

[CT Rain]

Isaac's surge was higher than Gustav's in most locations and higher than Katrina's in others. You're really saying it would not have helped to have that captured in an easy-to-interpret scale rating on the surge? So just as you are arguing that a Cat 4 SS rating would inspire concern and action, why wouldn't an easy to understand Cat 3 surge rating inspire concern and action as well (even though winds were only Cat 1)?

I disagree. I think we should de-emphasize with SS entirely but the last thing we should replace it with is another, more complex, scale.

I'm not sure what else people need the government and media to do.

There was a hurricane warning in effect with a lead time of 48 hours. There was a mandatory evacuation in place. There was a forecast of 9-12 feet of storm surge.

What more can be done???

I don't know what the local media was saying (so it's entirely possible they were downplaying, I'm not sure) but the products from the NWS and the evacuations seemed spot on to me.

[gymengineer]

Again, if I know I'm 5 ft above sea level, the single, most-important piece of information for me to know is the expected surge height, in ft-- not a category rating.

It does not work this way with wind-- I don't know the exact wind speed that will cause structural damage to my house.

If Isaac's surge was under-forecast, that is a problem with the forecast, not the style of communication-- i.e., whether the threat was conveyed in ft or a category assignment. Separate issue.

The designation "major hurricane" is only based on winds and moves people towards action, including public officials. All I'm saying is that with extended use, such a scale for surge might do the same.

[HurricaneJosh]

I disagree. I think we should de-emphasize with SS entirely but the last thing we should replace it with is another, more complex, scale.

I'm not sure what else people need the government and media to do.

There was a hurricane warning in effect with a lead time of 48 hours. There was a mandatory evacuation in place. There was a forecast of 9-12 feet of storm surge.

What more can be done???

I don't know what the local media was saying (so it's entirely possible they were downplaying, I'm not sure) but the products from the NWS and the evacuations seemed spot on to me.

Agreed-- except I still think the SS scale has value and should be kept.

My impression, being on the ground in LA, is that the threat was well-communicated and well-heeded.

[HurricaneJosh]

The designation "major hurricane" is only based on winds and moves people towards action, including public officials. All I'm saying is that with extended use, such a scale for surge might do the same.

I agree with you that the term "major" can be problematic, in that its omission can perhaps create a false sense of security in a situation where a 70-kt cyclone is producing a "major" surge.

[gymengineer]

I just feel the NHC did a very good job with this one, despite the crazy model divergences.

I agree with this completely. Nothing in their forecast was inadequate. This discussion is more about social science and what spurs people to act. While there weren't more deaths, many people did have to be rescued during the storm who should have evacuated.

[gymengineer]

Like, would more mandatory evacuations have been ordered before the storm (like in Slidell) if the storm had been called "major?"

What was the cause of all these water rescues being necessary for people trapped in their attics? It's useful to figure it out.. Wherever the breakdown occurred..

It's certainly not the hurricane center's fault, but too many did stay behind.

[HurricaneJosh]

Like, would more mandatory evacuations have been ordered before the storm (like in Slidell) if the storm had been called "major?"

What was the cause of all these water rescues being necessary for people trapped in their attics? It's useful to figure it out.. Wherever the breakdown occurred..

It's certainly not the hurricane center's fault, but too many did stay behind.

Well... Enough with these trivial life-and-death topics. Did you like my chase?