I realized that my answer to this question in THIS BLOG is too long. I just updated this with some more information ahead of Helene.
Here’s the short answer. You’ll need the elevation of the finished floor of your house. This will be on your building plans, survey perhaps or an Elevation Certificate prepared by a land surveyor. What you’re looking for is something like: “FF Elev = 9.1′ (NAVD 88)” or “FF Elev = 9.1 NGVD 1929”.
Now go to the NOAA site and find the tide station closest to your house. Let’s say that your house is near the “East Bay” tide station inside Tampa Bay. On this tide station page click on the “tide/water levels” and select datums. Now set the datum to NAVD 88 and note the Mean High High Water. In this case it’s +0.86′ by the NAVD 88 Datum, the same one used for your house, let’s call that +1′ by the NAVD 88 datum. NOTE THAT THE ACTUAL TIDES HAVE BEEN RUNING ABOUT 1′ HIGHER THAN THIS BUT NOAA PREDICTS STORM SURGE BASED UPON THE HEIGHT ABOVE THE MEAN HIGH HIGH WATER (MHHW) So, when NOAA predicts say a 12′ surge it is 12′ above this MHHW level.
So for our example, basically, for this house there is ABOUT 8′ (9.1′-1′) of differance between the calculated mean high high water, at this sensor with no hurricane, and the finished floor elevation of your house. Anything more than a dead flat predicted 8′ surge and your floor is wet.
Now, what about the other number, the 1929 NGVD elevation? According to the SW Florida Water Management to convert the older 1929 datum to the new 1988 DATUM one would SUBTRACT ABOUT 1.1′. So, for our example IF 9.1′ is given on the plan or elevation certificate you found in the older 1929 datum then this would be ABOUT 8.0′ in the now used 1988 datum. So now there’s basically there is ABOUT 7′ of differnence between the high water, at this sensor with no hurricane, and the finished floor elvation of your house. Anything more than a dead flat 7′ surge and your floor is wet.
Please keep in mind to hide from wind and run from water. This simple example does NOT include localized flooding effects or say wind driven waves or another house floating into your house. Be smart. GET OUT!
