Bill Read's Blog: What if Isaac hit Houston?
After looking at the dramatic flooding occurring with Isaac, how would the Houston-area fare with an Isaac-like storm?
For New Orleans, the event started Tuesday after Isaac arrived with a strong storm surge along the coast. People had been warned of pending flooding from surge and rain, and evacuation orders were in place.
Many people chose not to heed the warning.
After landfall, Isaac stalled and the incredible rainwater flooding was underway. The winds were still blowing onshore, causing the storm surge to remain high.
Now let us imagine Isaac coming to our area.
From a forecast and preparation viewpoint, the fact that Isaac remained at tropical storm intensity until right before landfall means that many people would not take it seriously, “it’s just a tropical storm”.
Throughout my career in the National Weather Service, I heard people say “I had no idea it would be this bad." Folks, there is no such thing as “just a” with these things. Same goes for “minimal hurricane.” We should know this to be true given our disaster with Allison in 2000. Speculation is the number one reason that a lot of people would have been unprepared in our area if an exact replica of Isaac made landfall near Freeport. It would have slowly meandered inland for nearly two days.
The impacts from the winds would be more widespread than most people would think. Prolonged winds would come in around 50 to 60 mph range with higher gusts that lead to significant power outages, as well as trees and limbs downed. Damages could easily top $1 billion dollars from wind alone.
The surge from a large 65 to 75 mph storm making landfall near Freeport would range from 6 to 9 feet in Galveston Bay. Because the winds continue over the Gulf and Bay, the storm surge would not recede for at least a day. At the same time, over a foot of rain, maybe close to two feet in some spots, could pile up over the two-day period causing extreme flooding on our bayous. The flood waters of the bayous would all flow to Galveston Bay. Then with the water level of the Bay already elevated from storm surge, the flow from the bayous would be unable to do so as quickly.
I speculate that the flooding in the communities in southeast Harris County and eastern Galveston Counties would be worse due to the combined effects of rain and surge. Modeling such an impact for forecast and warning is quite a challenge, but scientists, Rice University and other institutions have been working on a scenario just like this one. I trust they will succeed in creating an accurate prediction, but hope we never have to use it!
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