Post-storm Wind Analysis of Hurricane Wilma by HRD

[ekal]

Hi all,

While browsing the Hurricane Research Division's website today, I found the wind analysis for Hurricane Wilma while the storm was over South Florida. It can be viewed here:

http://www.aoml.noaa.gov/hrd/Storm_page ... /wind.html

Basically, the graphic suggests that a healthy swath of South Florida received maximum sustained winds of at least 80 knots. This seems strange to me for a couple of reasons:

1) Fort Lauderdale International Airport, Miami International Airport, and WFO Miami recorded maximum sustained winds of 61 kts, 58 kts and 57 kts, respectively (not even hurricane force). I am not aware of any of these anemometers failing in the storm. However, HRD has the three stations receiving a solid 80 kts.

2) I watched Wilma blow through Kendall, and I really don't think I saw anything near 80 kts sustained (maybe 80 in gusts, if that).

Additionally, the map suggests Wilma was a Cat. 2 at landfall on the SW Florida coast. Max sustained winds are shown to be only 95 knots over the coastal waters there.

What do you guys think about this analysis? Does anyone know how it was performed?

[MiamiensisWx]

In southwest Florida, the graphic indicates a maximum sustained wind (1-min) of 97 kt, which is rounded to 100 kt (Category 3 intensity) per TPC's standards.

Over land, it should be noted that it's an experimental product that utilizes many factors, including integrated kinetic energy, ground observations, and other data. The winds in the graphs may not be standard 10-meter values. Some estimates (especially in accelerating tropical cyclones like Wilma) may be high biased in the end. Wilma's strongest winds were concentrated in the eastern eyewall, and I don't believe these graphics take trees, shrubbery, structures, and other factors that inhibit exposure over land into account. These obstructions tend to reduce winds over land. I believe these grid surface wind values are quite fragile, so there is room for low or high biases depending on data ingestion.

[Derek Ortt]

at RSMAS on Virginia Key, we did have sustaiend hurricane force winds with gusts to about 110 mph during Wilma. I also saw a lot of debris (likely the Seaquarium) flying by my office window.

This was also about 10 miles south of the eyewall

Lake Okeechobee did have solid sustained category 2 winds. Based upon that, the HRD analysis at landfall MAY be on the low side, but in the mid cat 3 range (while I often disagree with NHC on landfall intensities, NHC likely got Wilma correct)

Wilma is a good reminder as to how destructive category 1-2 winds are in a major city (if Charley was not enough of a reminder the year before)

[Recurve]

It does give an interesting picture of why there was so much storm surge damage in the Upper Keys -- near 80 knot sustained winds pushing right into the corner of Florida Bay. Wilma brought the worst damage seen in at least 20 years on the bayside here. Though the shallow water and relatively short fetch kept the water from pushing very far inland on the Keys, the sloshing destroyed nearly every dock on the bay from Marathon to Key Largo.
I really appreciate the H*wind perspective giving a more precise view of overall storm windfields.

[CrazyC83]

The maps show that Wilma actually had re-strengthened over land into a Cat 3 once again (at 1430Z) as it re-emerged in the Atlantic...

[Derek Ortt]

3 weeks after Wilma, the streets of marathon wer elined with debris. I believe that entire island went under water as they had a surge at Marathon of 10 feet

[HurricaneBill]

3 weeks after Wilma, the streets of marathon wer elined with debris. I believe that entire island went under water as they had a surge at Marathon of 10 feet

Had Wilma moved a little more to the south, the Keys would have been in big trouble.

[CrazyC83]

3 weeks after Wilma, the streets of marathon wer elined with debris. I believe that entire island went under water as they had a surge at Marathon of 10 feet

Had Wilma moved a little more to the south, the Keys would have been in big trouble.

It would have only needed to go about 20 miles to the south, and that would have likely brought a 12 to 15 foot surge to the Keys. It would have been larger than the Labor Day Hurricane for sure (remember, that storm was tiny...Wilma at that point was much larger).

[Derek Ortt]

the eyewall missed Key West by 5 miles

We may have came that close to a repeat of Galveston since nobody seemed to heed the evac order

[Category 5]

the eyewall missed Key West by 5 miles

We may have came that close to a repeat of Galveston since nobody seemed to heed the evac order

Absolutely. I don't think people understand just how close we were to having a storm worse then Andrew.

[CrazyC83]

the eyewall missed Key West by 5 miles

We may have came that close to a repeat of Galveston since nobody seemed to heed the evac order

Absolutely. I don't think people understand just how close we were to having a storm worse then Andrew.

More like worse than Katrina in terms of loss of life potentially...the highest point on the Keys is like 10 feet above sea level?

[Category 5]

the eyewall missed Key West by 5 miles

We may have came that close to a repeat of Galveston since nobody seemed to heed the evac order

Absolutely. I don't think people understand just how close we were to having a storm worse then Andrew.

More like worse than Katrina in terms of loss of life potentially...the highest point on the Keys is like 10 feet above sea level?

Low enough to have been submerged completely.

[Recurve]

Highest point in the Upper Keys that I know = about 16 feet (natural feature on Windley Key) and possibly same in Key Largo on the crown of U.S. 1 -- road bed on top of the old railroad embankment.

I can't think of a monster storm that directly struck the Keys from the backside first, with the front right quad moving through Florida Bay. Who knows what kind of surge that would make.
Wilma's surge didn't reach U.S. 1 in Key Largo. The slope is pretty steep on the bayside and the water went in only a block or so. farther down it did reach U.S. 1 for sure.

[MiamiensisWx]

Highest point in the Upper Keys that I know = about 16 feet (natural feature on Windley Key) and possibly same in Key Largo on the crown of U.S. 1 -- road bed on top of the old railroad embankment.

I can't think of a monster storm that directly struck the Keys from the backside first, with the front right quad moving through Florida Bay. Who knows what kind of surge that would make.
Wilma's surge didn't reach U.S. 1 in Key Largo. The slope is pretty steep on the bayside and the water went in only a block or so. farther down it did reach U.S. 1 for sure.

I can recall two hurricanes (1906 and 1909) that moved NE across the Florida Keys at Category 3 intensity in October. The 1906 storm was particularly deadly (more than 100 railroad worker deaths), and several of the deaths were related to sunken houseboats or the surge, but I haven't found any definite information about the surge height in this TC and the 1909 event. It seems probable that breaking waves may have been more significant than the actual surge, which also occurred in the 1935 hurricane, though that TC featured a much larger (~18 foot) surge. It is interesting to note that most of the worker deaths during the Overseas Railroad's entire construction (1905-1916) occurred during the 1906 and 1909 hurricanes. The project was actually quite safe during most times, despite its audacity and challenges. It's definitely an "Eighth Wonder of the World"...

I'm betting that Wilma also featured breaking waves that were higher than the surge in the middle and upper Keys.

[Derek Ortt]

I am not sure that waves were a problem

Waves are a function of water depth, and Florida Bay is not exactly deep. On the Atlantic side, waves would likely be a greater problem as the water is much deeper there

[CrazyC83]

Highest point in the Upper Keys that I know = about 16 feet (natural feature on Windley Key) and possibly same in Key Largo on the crown of U.S. 1 -- road bed on top of the old railroad embankment.

I can't think of a monster storm that directly struck the Keys from the backside first, with the front right quad moving through Florida Bay. Who knows what kind of surge that would make.
Wilma's surge didn't reach U.S. 1 in Key Largo. The slope is pretty steep on the bayside and the water went in only a block or so. farther down it did reach U.S. 1 for sure.

I can recall two hurricanes (1906 and 1909) that moved NE across the Florida Keys at Category 3 intensity in October. The 1906 storm was particularly deadly (more than 100 railroad worker deaths), and several of the deaths were related to sunken houseboats or the surge, but I haven't found any definite information about the surge height in this TC and the 1909 event. It seems probable that breaking waves may have been more significant than the actual surge, which also occurred in the 1935 hurricane, though that TC featured a much larger (~18 foot) surge. It is interesting to note that most of the worker deaths during the Overseas Railroad's entire construction (1905-1916) occurred during the 1906 and 1909 hurricanes. The project was actually quite safe during most times, despite its audacity and challenges. It's definitely an "Eighth Wonder of the World"...

I'm betting that Wilma also featured breaking waves that were higher than the surge in the middle and upper Keys.

Was the 18 foot surge verified or exaggerated? That seems quite large for such a small storm in the Keys...a direct hit by Wilma would have likely had a higher surge even though she was much weaker...

[Recurve]

The 18-foot measure for the '35 Labor Day Hurricane is based on the surge overtopping the railroad platform at Long Key I believe. The grade heights were well documented and there are eyewitness accounts of the surge from survivors. One man whose account is in the official weather bureau reports on the storm ended up in the top of a palm tree on Long Key.
I'm not sure if we're certain of the exact surge height vs. waves on top of surge. Railroad ties were ripped from the top of the Long Key Viaduct. There were surges from both oceanside and bayside as the storm passed.

[MiamiensisWx]

I have one question. The 1935 hurricane and Charley 2004 were similar in terms of size, wind radii, and rapid intensification, so why did Charley produce a much lower surge than the 1935 TC? The "damming" effect of the railroad embankment (mentioned by Recurve in an older post) likely contributed to the height of the 1935 surge, but that TC arrived from the deeper offshore waters of the Atlantic. That should reduce surges on the east coast of FL, unlike the shallower Gulf Coast shelf, which induces higher surges.

Does anyone think the higher Gulf Coast surges may apply only to tropical cyclones with large wind fields, while greater storm surges are produced by smaller, intense hurricanes (i.e. Andrew and 1935) on the Atlantic side? In other words, Katrina-sized hurricanes would produce larger surges on the Gulf side than a Katrina-sized TC on the Atlantic side, but a rapidly intensifying, compact TC would induce a higher surge on the east coast of FL than a similar storm on the Gulf side. Note that the largest storm surges on the east coast of Florida have resulted from small, extremely intense monsters (16.9 feet at Cutler Ridge in Andrew and 18 feet at Long Key in 1935), while the highest surges on the Gulf Coast have been from larger storms such as Katrina, Ivan, et al.

Does that make sense?

[MGC]

The slope of the shelf is a major factor. Deep water is a short distance off the Florida east coast while along the gulf coast you have to go out much futher to reach deep water....MGC

[Tampa Bay Hurricane]

Hurricane Wilma had a large wind field. The tropical storm force
winds look like they extended out 200 miles from the center, with the
hurricane force winds easily 120 miles from the center (this is an estimate
only).