Wed Oct 19 2005 01:27 AM
Re: Another Look


I hope this isn't the wrong place to ask this, but I'd like some information on storm surge with a Cat 4/5. I know about being on the "good" side vs "bad" side. I learned a lot about surge from Katrina. So my question is, does the surge stay with the storm or does it expand out, like dropping a rock into a pond? What are the surge implications at the point of the hard right turn?

In other words, even if you're on the 'good' side, do you still have to worry about surge ahead of the storm?


Storm surge varies with the topographical layout of the near shore marine bottom.. If you have a sharp declination in oceanic depth very close to the shore, the storm surge of a cat 4 hurricane (for example) won't be as inland inundating as one that occurs where there is a long distance of shallow water... The reason is that the mass carried along with the storm surge in shallow water does not have as readily, a means to disperse before impacting elevations higher than absolute sea-lvl.

The point is, much goes into the calculations for storm surge. There are models on line now specifically designed to calculated surge potentials per wind speed, for various locations.. I'm not a regular user of those products, though, so you'll have to do a little research to find them.

There are some general guidlines however, that can be used for categories of storms and their counterpart surges:
Category One Hurricane:
Winds 74-95 mph (64-82 kt or 119-153 km/hr). Storm surge generally 4-5 ft above normal.
Category Two Hurricane:
Winds 96-110 mph (83-95 kt or 154-177 km/hr). Storm surge generally 6-8 feet above normal.
Category Three Hurricane:
Winds 111-130 mph (96-113 kt or 178-209 km/hr). Storm surge generally 9-12 ft above normal.
Category Four Hurricane:
Winds 131-155 mph (114-135 kt or 210-249 km/hr). Storm surge generally 13-18 ft above normal.
Category Five Hurricane:
Winds greater than 155 mph (135 kt or 249 km/hr). Storm surge generally greater than 18 ft above normal.

...These values are then augmented based on particular incidences of coastlines being impacted...

Oh, and to answer your question - the "good side" is always better... If a storm has a 20ft surge, they are not meaning the area with offshore wind components...they are talking about areas in the eyewall where the winds are normal to the coast - the surge values tend to drop off considerably outside the eyewall, then taper more gradually in the tropical storm force areas..

Note: This is NOT an official page. It is run by weather hobbyists and should not be used as a replacement for official sources. 
CFHC's main servers are currently located at Hostdime.com in Orlando, FL.
Image Server Network thanks to Mike Potts and Amazon Web Services. If you have static file hosting space that allows dns aliasing contact us to help out! Some Maps Provided by:
Great thanks to all who donated and everyone who uses the site as well. Site designed for 800x600+ resolution
When in doubt, take the word of the National Hurricane Center