NHC didnt do horrible on the surge forecast for Katrina:

[brunota2003]

bump...

[mf_dolphin]

One comment about the waves. While the waves occur along the coast, the water they carry with them piles up on top of the actual surge further inland and in bays. With an on-shore wind this water can't escape and therefore builds. That may be one reason the Ixolib didn't have and waves per se and yet he had very high water. I think Cantore had some of the same thing. I remember that there was a creek close by to the building they were in. This is teh nightmare scenario for Tampa Bay as well. A storm that come s ashore in mid Pinellas County would bring an onshore wind and surge into Tampa Bay with no escape route. We been cautioned here to expect surges 25-30 percent higher than the Saffir- Simpson scale for that reason.

[Recurve]

Have to repeat that I'm 100% behind the NHC, want to discuss the advisories and effects but not be critical of their performance. I know too that local NWS FO is important and has to be listened to for local advisories.

Ixolib, I'm interested in the back bay flooding issue. In the Keys, Florida Bay stumps some residents who are convinced we are vulnerable to a huge surge from the Atlantic but can't be flooded from the bayside.

I know you've probably posted more details elsewhere. Wondering if the surge you had was Atlantic surge pushing into the bay, or caused by winds on the bay?

My guess, it's hard too to know if water in someone's yard is from level surge or waves. A wave on top of surge rushes inshore and brings water to an area above the surge; the wave-carried water stays; it looks like level water but it was waves that brought it there.

This may be a crappy analogy, but the sea-level rise from a tsunami is inches until it meets the sloping seafloor and breaking wave moves inland. So is that surge or waves on top of the surge?

Seems ultimate high-water lines might be so much higher than the actual surge, or even the wave heights reported -- if a moving mass of water a few feet deep meets a cliff or wall with enough force, the water can run upwards and flood something much higher -- but the "surge" was never that high.

They say local topography and direction of approach matters. But do people realize that the same surge could leave one house at 15 ft. above MSL dry and flood another house nearby that's at 30 ft? I'm thinking that pathways can lead water to a 30' high house while the surge bypasses lower areas. If waves break over one part of a barrier island and reach a protected water body, shore areas would flood even though the barrier island directly in front might not have been overtopped.

Thing that scared me out of the Keys for Rita was the flooding in St. Marks and Shell beach (?) area from Dennis -- people thought they were so far east of the center they wouldn't have 3 feet or more of water on their streets and yards.

[Recurve]

Dolphin, good post. That's what I was trying to say.

[Agua]

Here's the breakdown, in my uneducated opinion:

1. Storm was Cat 5 approximately 1 day from landfall on MS Coast in a location where all the water was being pushed into the bend which forms SE La and Miss Coast.
2. The windfield was HUGE at this point (and up through landfall), moving water from a vast area of the gulf into the "bend" area.
3. It didn't weaken from the 175 mph monster until just prior to first landfall, so the water continued to pile up.

It's just plain common sense. A storm of that strength, at that location, with that large a windfield pushed a hell of a lot of water into an area from which it couldn't escape; much like the exaggerated surges experienced in the big bend area of florida from a north moving storm.

[f5]

as far as surge bays&inlets go no other states has those kinds of feature except NC the way the coastline is shape surge can do some very wacky things beacuse you have bays ,barrier islands,sounds,estruaries ect

[Ixolib]

Ixolib, I'm interested in the back bay flooding issue. In the Keys, Florida Bay stumps some residents who are convinced we are vulnerable to a huge surge from the Atlantic but can't be flooded from the bayside.

I know you've probably posted more details elsewhere. Wondering if the surge you had was Atlantic surge pushing into the bay, or caused by winds on the bay?

Recurve - we were here in the house as the surge came up. There was no "rush" of water, and certainly no waves as we are well protected to our south where the wind was blowing from (Keesler AFB borders my back yard). The water came up from the bay, but it's not a small bay with narrow inlets. The outlet to the Gulf is actually quite large - at least three miles across. This water came up fast, but it was a level rise the ENTIRE time. Once it reached its peak, it stayed for a couple of hours and then s-l-o-w-l-y began to receed.

The surge was definitely pushed into the bay, and subsequently, into our neighborhood and houses. For those who live at the same proximity I do to the bay, but on the north side, their houses were literelly destroyed because of the waves from the bay ON TOP OF the 30+ foot surge. Take a look at Porto Bay, Langley Point, Racetrack Road in D'Iberville if you can find the pics on the net. They are on the north side. But if you look at Bayview Avenue (on the south side of the bay), most of those houses are still standing because there was no wave action. Only a 30+ foot storm surge with level lines throughout their homes. For that matter, compare the NOAA pics on the north side of Biloxi Back Bay with those on the south side. BIG Difference in destruction. I'm very thankful we live south of the bay, and therefore, had absolutely NO WAVES!! But we did have plenty of water in the house... And we're 30 feet above MSL.

[Agua]

Ixolib,
You know what is bizarre? Oh the OS side, north Fort Bayou, the water doesn't appear to have risen even 5 feet so as to disturb ANY of the piers / moorings. So odd.

[Edit to include the following:] Go look behind Aunt Jenny's / Anthony's in OS.

[brunota2003]

Storm Surge:
An abnormal rise in sea level accompanying a hurricane or other intense storm, and whose height is the difference between the observed level of the sea surface and the level that would have occurred in the absence of the cyclone. Storm surge is usually estimated by subtracting the normal or astronomic high tide from the observed storm tide.

[Recurve]

Ixolib -- Thanks, that's a great eyewitness account, I really appreciate the explanation.

[Ixolib]

Ixolib,
You know what is bizarre? Oh the OS side, north Fort Bayou, the water doesn't appear to have risen even 5 feet so as to disturb ANY of the piers / moorings. So odd.

[Edit to include the following:] Go look behind Aunt Jenny's / Anthony's in OS.

Good point Agua, and it's the bizarre that keeps us so interested in this stuff, isn't it!!

We ate at Aunt Jenny's just the other day. It was our first "going out meal" since the storm (Mmm Mmm Good)!! Anyway, you are right about the piers there. But also, remember those establishments are on the SOUTH side of Fort Bayou and therefore, were protected from the wave action because of the land mass of Ocean Springs. Anthony's, by the way, did take a pretty good hit from plain surge, but because there were no waves, the building stood. Also, the piers on the south side faired well too because they simply went underwater pretty quick and were therefore well protected from the wind/wave action.

Now, if you're sitting in Aunt Jenny's and look north just a few hundred yards across Fort Bayou, you will see that virtually EVERYTHING on the shoreline there was either destroyed or severely damaged. In fact, as many may recall, that is where Gulf Hills is located and that neighborhood took a major hit -- to include a few deaths.

I'll agree that the surge in that area of Fort Bayou was not 30 feet - but that area is also quite a distance from its outlet/inlet into Biloxi Bay. Had there been 30+ feet of surge there, I believe the Fort Bayou bridge (at least the north end) might have been in the same shape as the O.S. bridge, B.S.L bridge, and the Popps Ferry Bridge. We're all very lucky the Fort Bayou bridge survived intact!!

For a contrary perspective, when Elena, Georges, and Frederick (and even Ivan to a small degree) hit, ALL the piers on my side of the bay (south side) were destroyed. Reason being that those storms were either slightly or well to our EAST, and hence, the northerly winds (plus relatively small surge) pounded those piers straight on. However, in Katrina, many of the piers on my side of the bay faired pretty well. First off, they went well underwater pretty quick and secondly, the water was pretty calm on this side. Again, NO waves since the wind was from the S and SE throughout.

And speaking of the Popps Ferry bridge, that's a great example (with greater proof of 30+) of surge plus wave action - but, we'll leave that for another thread.