Coastal weather events come in all shapes and sizes, as does the impact they have on the Southwest Florida Coast. Naturally, the two are correlated - though not always in the way you might think.
1. Size matters: A tightly wrapped, intense storm can do a lot of damage in a small area. But a broader, less windy storm that is slower moving can be even more destructive, by affecting a broader area with still-punishing winds, a more significant storm surge and storms bands spiraling off heavy rainfall and tornadoes. When it heads inland, the threat of flooding from a disintegrating storm puts the final touches on its power.
2. Duration does, too: A fast-moving storm hits and moves on. A slow-moving one just grinds away, piling on rainfall and erosive waves for hours and even days. A great example of the power of persistence was tropical storms Debby and Isaac this year. Tropical Storm Debby never made it to hurricane strength but, by spinning away out in the Gulf of Mexico for more than two days, it scoured west Florida beaches in a way not seen in decades while its rainfall-driven flooding ended up causing just one less fatality than a far more intense storm (with twice the wind speed at peak) that sped through the same general area. Hurricane Isaac was a slow-moving storm that sent torrential rains all through southern Louisiana.
3. Category rating doesn't gauge impact: Hurricane Isaac barely crossed the 74-mph threshold before making landfall south of New Orleans, but it carried with it the storm surge of a much stronger storm.
Why?
It was large (if not well organized) and it had a couple of days to push water out ahead of it resulting in a surge that rivaled Hurricane Katrina in many places even if the wind was nowhere near as strong. It reminded the weather pros that focusing on a storm's category can underestimate its true strength.
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Founded in 1926, the American Shore & Beach Preservation Association provided this information.
4. What wind can't do, water does: Hurricane Isaac's nominal hurricane-force winds weren't the issue on Gasparilla Island.
It was the significant storm surge, inundating rainfall and slow forward motion that made this system significant in terms of destruction. Folks along the Sun Coast got sloshed with surge while those inland had to cope with swollen rivers and overwhelmed dams.
Isaac wasn't windy but the compounding catastrophe of deluge and duration made it a major storm event.
5. Gauging damage: We've seen this phenomena a couple of times recently: Middling tropical storms bring maximum destruction when they drive far inland. Either their weakened winds are still potent enough to wreak havoc on a landscape unused to such strength or abundant rainfall pushes rivers and streams into disastrous torrents. Hurricane Irene devastated towns in the Northeast that hadn't seen rainfalls of such magnitude in decades. TS Debby combined flash floods with tornadoes to cut a swath through the Southeast. Isaac ripped into the Gulf Coast with a watery combination of surge and downpours, put thousands underwater or in the dark and, in a bit of a silver lining, ultimately, brought much-needed rainfall to the parched Midwest.
Summary: As surprising as these storm strengths may have been, pre-storm preparations and plans worked and made the storms more survivable. Coastal areas with wide beaches could withstand hours and days of battering waves - because the beaches took the hit, not the upland properties and infrastructure. The billions spent to protect New Orleans post-Katrina withstood its first real test, and passed with flying colors. People heeded the calls to evacuate coastal areas threatened with inundation while those who did not often put themselves and the first-responders who had to go out in the midst of the storm to rescue them at real risk.
