Friday, September 8, 2017

Expect Localized Storm Surge Maximum of 14-16 ft in SW FL and FL Keys

Hey everyone- I apologize for the low-tech post here. I had 12 hour field work day and I'm just getting to computer now.

Here are some thoughts on Irma's storm surge potential...

Irma will generate a life-threatening storm surge in the FL Keys and SW Florida.

Irma's forecast track shifted west today, and the storm also appeared to grow in geographic size and re-intensify back to a category 5 hurricane. This is a worst case scenario for Middle and Lower Keys.


I don't understand the official forecast of a 5-10 ft storm surge in the Keys. Observational data of other extreme hurricanes in this area would suggest a widespread 10-14 ft storm surge in the Middle and Lower Keys, with localized maximum in the 14-16 ft range. Storm surge likely 6-10 ft in the Upper Florida Keys (Key Largo).

1) The Labor Day Hurricane (1935) was a compact/ small category-5 hurricane that generated an 18-foot storm surge in the Florida Keys. Irma's wind speeds will be lower than the Labor Day Hurricane, but the geographic size is larger. These variables somewhat offset each other, but the Irma's surge will not likely exceed the Labor Day Hurricane's high water mark. 

2) Hurricane Donna (1960) took a similar track as Irma and was a similar geographic size. However, Irma's maximum sustained winds will approach the Florida Keys in the 155-160 mph range, which is around 25 mph greater than Donna. The U-Surge Project has identified five high water marks exceeding 12 ft with a maximum water level of 13.7 ft during Donna. Irma should generate a higher surge than this.


A storm surge of 12-16 ft storm surge is possible in SW FL, in places like Naples and Marco Island....but this depends on exact storm track. If storm passes Naples and Marco Island to the east, surge levels would likely reduce to 6-10 ft.

Expect dramatic "negative" surge in places like Tampa Bay, where water will initially be pushed out of the bay, exposing vast mud flats. After Irma makes its closest approach, expect damaging winds in opposite direction to push water back into these bays with shocking speed and intensity. Wall of water will push back into west coast bays after eye passes....likely reaching levels of 3-6 ft above normal.


I am feeling more confident that metro Miami and points north, like Palm Beach and Melbourne, escape with less than 5 ft of storm surge. We will have to watch Irma's track closely to see if it approaches NE Florida or the Georgia Coast.

it appears at this time that Irma may track "up" the peninsula or remain closer to the west coast. If this is the case, the Atlantic coast should expect elevated storm surge levels and some flooding, but avoid catastrophic storm surge inundation.

The area of NE FL (north of St. Augustine), entire GA coast and SW South Carolina is quite susceptible to storm surge inundation, and could observe a prolonged storm surge even if Irma's center of circulation is 100 or more miles inland.


I am in the car a lot tomorrow (Saturday). Please email if you have questions or would like to do an interview. I will reply to you as soon as I am able. Thanks!



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