IS east coastal florida and fl keys protected from surge

[cpdaman]

I think it is *to a degree*

with cuba to the south and the bahamas off to the se and east it would appear to me that most hurricanes effecting this part of the state would observe less than standard storm surges although the forecast would probably still call for higher water rises due to either

not wanting to lull the public into unpreparedness or not fully being aware of this

i am not speaking about the areas from naples on the west coast northward to the panhandle.

but as anyone who surfs knows the florida keys and SE florida usually misses most of the hurricane surf due to all the land masses including great bahamian bank that block wave and swell energy, now when a 100 mile an hour storm is 30 miles offshore there will be waves but i think alot of the wave energy does not get to transverse the ocean and build up when it reaches these shores like it did in the gulf with katrina or in the carolina's or most anywhere else for that matter. it would take IMO a SW ward moving storm to really deal a great storm surge to the SE coast of florida (south of melbourne) and we all know this doesn't really occur.

take wilma for example forecast to have up to 17feet of surge, reported 7-8 feet in SW florida (note cuba would block/deflect a great deal of wave energy)

hurricane frances large cat 2 storm forecast 7-8 feet got less than 6 in (5.89 in st lucie lock)

same thing with Jeanne (6ft surge) with a fomidable storm

hurricane andrew and charley were extremely powerful but compact storms and thus there surge would be expected to be less relative to a katrina but they were on the order of

charlie 6 feet on sanibel island (based on visual) and 4 feet or so on the mainland beaches

andrew widespread 6-8 feet with up to 11 feet at burger king international headquarters (high water mark was higher there to do landfall coinciding with the time of high tide which in addition to the wind waves)

but really i think since most of the deaths due to storms are from storm surge that s. florida and the keys are surprisingly protected from high surges, with the exception being a CAT 5 storm like andrew which will demolish anything in its path

note a NNE/NE swell angle would produce the highes swell for the se coast of florida and NE swell angle for area from melbourne/ juptier due to the large open ocean according to this fetch which would be surprisingly apparent if one were to look at the wave heights during storms which aimed a long fetch in these directions i.e perfect storm 20 foot plus waves and subtropical storm andrea 14 foot waves/swell in the palm beach and se florida areas.

i beleive a relatively long tracking storm from these angles would have the most potential for a storm surge but the water where a storm like this would have to originate from are too cold and climatoligcally speaking unheard of.

[Recurve]

Interesting points.
I think Burger King, Matheson Hammock area had 18' in Andrew, not 11'.
The Keys in '35 had 18' surge in places. Of course both of those were small Cat 5s.
But it seems there's plenty of area to generate a full surge with a storm on the Florida side of the Bahamas or Cuba -- 100 miles or more of open water.
As many pros have said, the seafloor profile off south florida is not as shallow as off the northern Gulf coast, and shallow approaches are what cause the highest surges.
Also, what protects the Keys from ocean swells is the reef more than the Bahamas. Miami gets crashing waves that the Keys do not; the swell break on the reef and Hawk Channel is a surprisingly calm buffer along the coast.

[MGC]

Wilma put quite a bit of water in Key West despite passing offshore. I would not want to get caught in the keys during a big hurricane....MGC

[cpdaman]

as i mentioned in my post the "high water" mark was higher due to the astronomical high tides which was occuring as the surge hit of 18 feet , the storm surge value attributed to the rise i believe was significantly lower

the keys experienced a 6-8 foot surge of water built up from the atlantic side as wilma approached

on the keys side there is appox. 90 miles of water and on the east coast side there is generally 70-90 miles in places

miami does not get swell except from a N direction they may get 8-10 foot wind waves when a storm is on top of them (literally) but places like cocoa beach get this type of surf 6-8 times a year from regular low pressure systems (nor'easter types)

the keys never have have surf they will have about 3 foot wind whipped chop in a hurricane ( the bahamas do block swell that would be from an easterly direction but like you said the reefs block the wave action anyway, this IMO is why the keys don't get a strong wind swell building (like miami sees in a storm)

i would like the pro's take on this that a storm surge is really "handicapped" in building into the SE florida coast or the keys because of the lack of fetch or other reasons

in areas like miami, fort lauderdale, west palm beach, key largo, marathon, i find it difficult to imagine them getting a surge of 20 feet even from a cat 4 or 5 although i would never wish this on these cities. although i think key west might be able to get a good surge from a wnw moving storm along the cuban coast and then turning more north into the city

i am aware of the SLOSH model for predicting maximum potential surge but i believe it does not take into account the slope of the sea shore or the fetch of open water that the "wall of water" has to build up over.

[Normandy]

Andrew actually produced a storm surge of 17 feet in biscayne bay, had nothing to do with high tide.

If Andrew produced 17 being as little as he was, Katrina could have prolly approach 20 ft on the Fl Coast....had Floyd hit at peak intensity, prolly would have reach over 20 ft.

You have to remember that the surge of a hurricane is directly related to its windfield, and the larger the area of 65kt and 90kt winds, the higher the surge is going to be. For example, look at Katrina's surge of 28 feet. Had, lets say, Carla or Gilbert hit when they were at their peak (Wind maxima wise), then the surge could have been 30-35 ft.

[cpdaman]

actually it had plenty to do with high tide and you can read about it in http://www.nhc.noaa.gov/1992andrew.html

the 16.9 feet on the western side of the biscayne bay was a "Storm tide" the combination of storm surge and an astronomically high tide. i will concede the surge was probably 13 feet minus the astonomically high tide

hurricane camile was a small category five with 50 miles radius of hurricane winds it had a surge of 24 plus feet

[MGC]

Camille didn't have 50 mile radius of hurricane force winds. Kesler AFB, about 20 miles away from eye landfall had Cat-1 winds. Camille's radius of HFW was on the order of 25-30 miles.....MGC

[docjoe]

Given that radius of winds determines storm surge to a large degree what explains such high surges with labor day 35? It was a rapidly strengthening storm thus had minimal time with such high winds. Secondly the radius of hurricane winds was relatively small. Did the offshore topography cause it or when the winds get that high do the rules change to a degree??

docjoe

[cpdaman]

1. i would question the mark of 35 feet for the storm surge back in the day, wind waves could account for a significant rise in creating a high water mark, but i would question a 35 foot surge total.

2. i think wind radius determines the swath of the storm surge (amount of miles effected) and to a lesser extent it's acute (over small area) total surge height

[jinftl]

The website below shows projected storm surge flooding in Miami (and links to other cities like Tampa, New Orleans, Charleston as well) for various storm categories. Definitely any of the barrier islands (including Miami Beach) in South Florida are at risk for storm surge flooding (all accounts of the 1926 hurricane tell of Miami Beach being totally covered with water).

Also, I believe I have read that the coast of South Florida is more vulnerable to high wave action, which can compound any surge flooding...but i will let the experts confirm that.

http://www.environmentaldefense.org/article.cfm?contentid=5353

[Aric Dunn]

just a couple things to add..

distance that wind blows over water is called "fetch" so the wind radius can be refered to as such.

second i did not see anyone mention pressure.. storm surge is partially attributed to the low pressure near and at the center.. the largest increase of surge is as the eye makes landfall .. so andrew, katrina camille, all very low pressures at landfall... verses say frances , and jeanne not so low. and there are always exception.. depending on forward motion of the storm and angle of approach as well as the actual coast.. if its a bay etc..

pressure . plays a larger role in how high the surge can be ..

wind can only do so much ...

[MGC]

One inch of merury equates to about 13 inches of water if I recall correctly. So, a really intense hurricane will at most have 2-3 feet of surge caused by lowered atmospheric pressure. The majority of surge is water trapped against the shore cause by the extent of strong winds blowing the water shoreward......MGC

[Aric Dunn]

One inch of merury equates to about 13 inches of water if I recall correctly. So, a really intense hurricane will at most have 2-3 feet of surge caused by lowered atmospheric pressure. The majority of surge is water trapped against the shore cause by the extent of strong winds blowing the water shoreward......MGC

need to find the exact numbers please.. ?

[Aric Dunn]

well besides .. the likelihood of there being slight discrepancies this link is good.. its from wikipedia

http://en.wikipedia.org/wiki/Storm_surge

[Aric Dunn]

At least five processes can be involved in altering tide levels during storms. These include the pressure effect, the direct wind effect, the effect of the earth's rotation, the effect of waves, and the rainfall effect (Harris 1963).

actually addresses south florida pretty good..
in that previous link

good graphic.. showing the difference in pressure verses wind driven

[Derek Ortt]

The Atlantic side of Florida (including the Keys) has something called deep water.

Do not compare Charley. Had it have had even Andrew's size, it would have caused a 20 foot surge

[cpdaman]

thank you ARIC you bring up a great point with pressure , seems i underestimated it

and thank you derek the deep water off the coast would indeed help prevent very high surges

[Aric Dunn]

there is one big problem .. that we forget on the east coast.. something called
"rogue waves"

you may or may not have heard of them.. but the gulf stream is notorious for them?

[Aric Dunn]

http://en.wikipedia.org/wiki/Freak_wave

there is a link that helps with it even mention hurricane katrina..
there is evidence that during hurricanes .. these waves are even more common..
daytona beach was hit by a rogue wave that happened in the gulf stream ...

[jinftl]

Photo of Miami Beach from 1926 Great Miami Hurricane..this would not be a pretty sight on Miami Beach today....

http://www.palmbeachpost.com/storm/content/storm/about/history/26storm.html