As you may now by now I’m a Professional Engineer here in Florida and I am a Structural Engineer in Massachusetts where I was first licensed. I spent 2 years in St. Croix doing hurricane reconstruction work as an engineer. So, the question is: How much worse is a Cat 1 to a Cat 2, or 3 or 4 or a full blown 5?

OK, so as an engineer we design for wind loads as expressed in pounds per square foot or psf. What we do is we correlate between the wind speed and how that translated into a loading on a structure. Many items affect this equation. Things like the shape of the house, the height above the ground that the item being designed is at, how obstructed (or not) the area upwind is, etc. As you might imagine the math can get complicated when considering all these factors. We however will look at the older, simple method, of calculating wind load without any adjustments for these factors to answer this basic question. That Formula is: P = 0.00256 V^2. NOTE the V squared term.

Cat 1 is 74-95 mph, Cat 2 is 96-110 mph, Cat 3 is 111-129 mph, Cat 4 is 130-156 mph and Cat 5 is 157 mph or higher. Remember that V squared term. Thus, the load in PSF produced by the wind at various wind speeds is…

80 MPH	16.4 PSF
100 MPH	25.6 PSF
120 MPH	36.9 PSF
140 MPH	50.2 PSF

The difference in the wind load, the pressure in PSF on your roof and trees and the like, is that it triples from 80 MPH to 140 MPH and doubles from a 100 to 140 MPH wind speed. AND 50 PSF of wind uplift load is an ENORMOUS load to resist.

Which is why in a Cat 4 “Catastrophic damage will occur: Well-built framed homes can sustain severe damage with loss of most of the roof structure and/or some exterior walls. Most trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last weeks to possibly months. Most of the area will be uninhabitable for weeks or months.”

Hurricane Dorrian is now over the Abacos with sustained 185 mph winds or 87 psf. This is total devastation.

Here’s the question I get all the time. Does it pay to install new hurricane shutters or impact rated windows?

First, the market WILL pay a premium for a home with impact windows but this is about 60% of what you will spend to install them. Is it worth 60% of X for you to have the convenience of impact rated windows?

But I’ll save on my insurance. I hear this all the time. Perhaps and perhaps not. IF your home was built according to the 2001 (or later) Florida Building Code (FBC) then you already receive the maximum wind mitigation discount which is about 85% of the unadjusted premium. Changing out perfectly good shutters for impact rated windows will NOT save you any money. That’s because the building code, and your insurance company, see impact rated windows and storm shutters as the same building code required impact resistance under the post 2001 FBC.

What if you live in a home built prior to 2002? First, read this article on how to calculate the savings of wind mitigation upgrades. For homes built before the 2001 FBC then one can apply for various wind mitigation discounts for, amongst other items, Class A or Class B hurricane protection. The FBC classifies Dade & Broward counties as being in the ‘High Velocity Hurricane Zone’ (HVHZ) and construction in these counties is to a higher level of protection. HVHZ approved panels are what are commonly referred to as Miami-Dade County approved protection. If a property is located OUTSIDE of the HVHZ then one need only install FBC approved hurricane panels BUT Citizens will give a steeper discount for the HVHZ or Class A hurricane protection even though the building code does not require it there. So, in pricing out hurricane panels or impact rated windows look at:

• Do I already get this hurricane mitigation discount?
• Do I need to change out one window/door? Is it that I simply do not have a proper garage door or am I missing panels over a single opening someplace? Can I fix a small issue?
• If I need a full set of shutters (as I did) then what’s the cost of the Class A (HVHZ or Miami-Dade) Vs. Class B shutters/windows and what are my annual savings for one Vs. the other. I did the math and I chose to install a Class A steel hurricane panel protection system. My garage door was already code compliant.
• The same math as above will apply for “impact windows” which are “Miami-Dade” approved or Class A impact rated windows or may simply “FBC” impact rated windows. Note BTW that the slang nomenclature here is misleading as ALL windows, doors and shutters installed in Florida under a building permit are FBC approved.
• The pros and cons are endless and debatable when discussing hurricane panels Vs impact windows. I try to let the math make my decisions but I will say this. When the wind starts blowing sand around, the impact windows will get scratched and this cost big $$ to have the polished or replaced. If they take an impact then they may not breech but they still crack to the point that the glazing needs to be replaced, which again is expensive. Shutters are “tougher”. If they take a hit then they typically can still be used. Ultimately, impact rated windows area a luxury item. A chevy may get you back and forth to work but the Benz does it in style. Steel hurricane panels do the same job as impact rated windows at about 10% of the cost.

Now this is fascinating. I was just doing a blog post on correlation between the finished floor elevation of my house in North Palm Beach and basically when the forecast storm surge is such that I should be worried. In looking at the NOAA web site for the Lake Worth Pier and I found a plot that shows the MEASURED change in sea level since that station began reporting data. What I saw there astounded me.

CLICK HERE to see the trends of all the tide monitoring stations of NOAA.

“The plot shows the monthly mean sea level without the regular seasonal fluctuations due to coastal ocean temperatures, salinities, winds, atmospheric pressures, and ocean currents. The long-term linear trend is also shown, including its 95% confidence interval.”

“The relative sea level trend is 3.54 millimeters/year with a 95% confidence interval of +/- 0.56 mm/yr based on monthly mean sea level data from 1970 to 2018 which is equivalent to a change of 1.16 feet in 100 years.”

THIS GRAPH OF THE ACTUAL RECORDED SEA LEVEL AT THE LAKE WORTH PIER SHOWS THAT THE SEA LEVEL HAS RISEN THERE BY OVER 1′ IN JUST THE LAST 100 YEARS. (Note the graph is in Meters.) I would expect this to be similar to places along the coast such as Jupiter, Singer Island and Jupiter Island to be very similar.

I happen to live in a neighborhood that has pretty decent elevation BUT after looking at this I would NOT buy property between Indiantown road and the river for instance. This land is already low, the location along the river makes it susceptible to storm surge, and after seeing this trend this is going to get worse in the not too distant future.

The things I sit around thinking about. I just did a blog posting on the cool map that NOAA has to predict storm surge, and particular around Jupiter Florida.

The actual storm surge for Hurricane Idalie at Cedar Key.

The measured storm surge for Hurricane Ian.

The measured storm surge for Hurricane Helene at Cedar Key

CLICK HERE for the short(er) version of the answer to this question.

I wanted to see how the forecast surge aligned with my real world observations of the storm surge water levels at my house in Hurricane Jeanne in 2004. This led me to an interesting question. How can I tell how say a 5′ storm surge relates to the elevation of my house?

First my real world observation. I recently went through a whole bunch of work to file for and obtain a Letter of Map Amendment (LOMA) from FEMA for my house east of US-1 in North Palm Beach. During that process I asked the surveyor to locate and flag the 6′ NAVD 88 elevation contour in my front yard as this the Base Flood Elevation (BFE) shown on the FEMA FIRM. I remember where the water came up to in 2004 during hurricane Jeanne and that was with a reported 5′ storm surge at the FP&L power plant in Riviera Beach near me. The actual high water line at my house for Jeanne was indeed just below this 6′ contour and again, in our area the mean high high water line is at +0.55′ by this NAVD 88 datum. I also know (look at your Flood Elevation Certificate or building plans) the finished floor elevation of my house is +7.5′ NAVD 88. So does that mean that with say an 7′ storm surge, (7’+0.55′) is my first floor is wet or nearly wet?

Intuition would tell us yes and it turns out intuition is right in this case. Storm surge is the water level ABOVE the CALCULATED ocean water LEVEL ON THAT DATE. Storm surge is caused by the temporary effect of the wind and low pressure of a hurricane. It is added to whatever the tide happens to be when the storm hits. But tide calculations fluctuates based upon the time of the year, the cycle of the moon and even day (higher) vs night. In south Florida we are all aware of this and what we call the ‘King tides’ which happen to occur in, you guessed it, hurricane season.

First we need to ask what is mean high high water? Well, at the Lake Worth Pier the Mean High High Water (MHHW) is given as +0.51 ft ABOVE the NAVD88 datum. The CALCULATED high water line in at +0.51 ft using the same datum or reference line used by surveyors to show the elevations of my land and the first floor of my house. However this MHHW changes based upon where you are . If you want to know this then look at the NOAA tide station near where you live and the sensor information page.

Looking at my flood Elevation Certificate (EC) for my house I noted that my FF EL = 7.5′ (NAVD 88). Thus, if the forecast is for a 7′ storm surge ABOVE THE CALCUALATED MHHW OF +0.51′ then my house finished first floor should be wet. Always remember, hide from wind, RUN from water.

If you have an old survey or elevation certificate for your house which give the elevation of your floor in the 1929 datum then THIS POST will show you how to translate this to the newer 1988 datum.