Hurricane Irma quirk averted worst-case-scenario for storm surge

The U.S. Geological Survey will be collecting this week special storm surge devices it placed throughout the state before Irma made landfall Sunday.

But by all accounts, the surge was not as fierce as the up to 15-feet worst-case-scenario predicted over parts of the southwest coast.

While the Keys got wiped clean in some places, the counterclockwise swirl of Irm’a winds promised flooding of greater proportions over areas south of Naples north to Fort Myers and up the Caloosahatchee River.

In the end, it was Jacksonville that had the highest water levels.

A minor jog inland, seen on hurricane center track forecasts Sunday afternoon, sent surge into Naples and Everglades City, but complete devastation was averted.

Related: Full coverage of Irma’s aftermath.

Here’s how two things kept Florida from seeing worse from Irma:

From the very first stirrings of rising air and budding thunderstorms off the coast of Africa, Hurricane Irma had a red carpet through the tropical Atlantic, an atmospheric buffet table of warm seawater and light shear to nourish its growth.

Satellite image of 93L, which would become Irma, taken 3:45 a.m. EDT Aug. 30, 2017.

Its explosion from a tropical storm Aug. 30 to a Category 3 hurricane the next day was one for the record books. By Sept. 5, Irma was a violent Category 5 tropical cyclone with 185 mph winds — a power it would hold for a whopping 37 consecutive hours.

Irma decimated the northern Leeward Islands, raking over Barbuda and the Virgin Islands before setting on a furious path toward Florida.

But when the vulnerable peninsula faced worst-case scenarios that buzzed the powerful storm first up one side then the other, Mother Nature stepped in to tweak Irma’s plan.

By the grace of Cuba’s northern coast, which was abraded by Irma before the strong Cat 4 hurricane reached the Florida Strait , and a tongue of dry air sucked into its massive, state-swallowing wind field, the storm weakened slightly and couldn’t regain strength before making its first landfall Sunday morning at Cudjoe Key.

Hurricane Irma made landfall on Cudjoe Key at 9:10 a.m. Sunday, Sept. 10, 2017.

A subtle wiggle west that made Marco Island its second landfall target kept the deepest and deadliest storm surge away from Naples, Fort Myers and Tampa as fewer of the counterclockwise lashing winds were over the Gulf of Mexico.

“There are just so many little subtle things that can make all the difference,” said Jonathan Erdman, a senior digital meteorologist at Weather.com. “After it hit the Keys, it took a more due north path instead of north-northwest, and that drove the eyewall ashore near Marco Island, which started weakening it.”

At the same time, however, that western wobble put the east coast metro areas within closer reach of Irma’s 80-mile hurricane wind-span and 220-mile stretch of tropical storm-force winds. It also meant more flooding in Jacksonville, which suffered inundation from Irma’s southeast squall.

“It’s not over yet,” said Colorado State University hurricane researcher Phil Klotzbach, noting the flooding in Jacksonville and potential impact in Georgia. “We’re going to learn a lot from this storm, and it certainly could have been worse.”

In Palm Beach County, gusts of 91 mph were recorded at Palm Beach International Airport on Sunday evening as the most potent part of Irma blew through. Other preliminary high wind gusts include 79 mph in Boca Raton, 90 mph in Lake Worth, 84 mph in Juno Beach, 77 mph in Jupiter, 71 mph in Pahokee, 67 mph in Boynton Beach, 65 mph in Belle Glade, 56 mph in Delray Beach and 55 mph in Greenacres.

Massive black olive trees toppled by Hurricane Irma block South Olive in West Palm Beach on Monday. Sept. 11, 2017

“I think Floridians have had a good display of how if you are on the east side of a hurricane, you can be much worse off than on the west side,” said Dan Kottlowski, a hurricane expert at AccuWeather. “Hurricane Matthew passed about the same distance away from you that Irma did, but Matthew was to the east.”

The highest wind gust in Palm Beach County from 2016 Hurricane Matthew was estimated at 67 mph in Juno Beach.

Throughout the county, Irma’s gusty winds, along with sustained speeds of 58 mph at Palm Beach International Airport, uprooted trees, tore street lights from their perches, ripped signs from the ground, shredded shrubbery and cracked palm trees in half.

Kaylie Atteo of West Palm Beach was shocked to find five towering shade trees on South Olive Avenue stretched across the road, their roots lifting up sidewalks as Irma’s winds caught their canopies and took them down.

The intracoastal waterway splashes over the sea wall in West Palm Beach as Hurricane Irma moves through Florida, September 10, 2017. (Greg Lovett / The Palm Beach Post)

“I wrapped up my furniture and put it up on blocks because we just didn’t know what to expect,” said Atteo. “But I never thought these trees would go down because the storm went so far west.”

Atteo spent the night in Boynton Beach with her mother, but Steven Smilack, whose home is next to one of the massive downed trees, stayed. With shutters on his two-story home, he said he never heard the trees go over and didn’t know they had fallen until this morning.

“We just came out and saw what you are seeing,” he said.

By Monday morning, Irma was downgraded to a tropical storm and then a depression.

kmiller@pbpost.com Twitter: @kmillerweather

4 hurricane graphics you need to understand before June 1

The National Hurricane Center has released four hurricane graphics aimed at helping people better understand the risks posed by an approaching storm.

Some graphics are just tweaks to well-known products, such as the forecast track cone.

Check the Palm Beach Post storm tracking map.

But others are entirely new and could easily be misinterpreted.

Here are the four graphics and what they mean.

  1. Potential tropical cyclones: To improve alert times for tropical systems, the NHC will begin issuing advisories for potential tropical cyclones. These are systems that are not yet a tropical depression, storm or hurricane, but may become one as they near the coast. The forecasts for potential tropical cyclones will look the same as tropical storm and hurricane forecasts, but the track cone may be larger because there is less certainty in predicting where an unorganized system will go.
The National Hurricane Center will make forecasts on potential tropical cyclones before they meet the definition of tropical depression or storm.

2. Earliest reasonable arrival of tropical storm-force winds: So that people will have a better understanding of when preparations should be complete ahead of a storm, a new wind graphic will be used this year that shows when tropical storm-force winds will reach specific areas. The graphic contains the percent chance that the winds will impact an area and approximate time. A second graphic will show the most likely arrival time of tropical storm-force winds.

Example of the earliest arrival time of tropical storm-force winds.

Download the Palm Beach Post WeatherPlus app here.

3. Update to tropical cyclone advisory graphic: The NHC updated the look of its tropical cyclone advisory graphics with cleaner lines and softer colors. It also added an important new element with a circular mark in the forecast cone that shows the extent of hurricane and tropical storm-force winds. This will better illustrate the fact that damaging winds don’t always stay within the cone and people living outside the cone can still feel impacts.

Example of track cone with tropical storm-force wind field.

4. Storm surge watch and warning maps: The NHC will issue storm surge watch and warning advisories this year the same as they do for tropical storms and hurricanes. The storm surge watch means the possibility of life-threatening flooding from storm-related surge is possible within 48 hours. A storm surge warning means the danger of life-threatening flooding from rising water moving inland could occur within 36 hours.

Example of storm surge watch and warning map.

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New storm surge map shows deadliest areas during hurricane

Hurricane experts repeat a mantra that more people die from storm surge than high winds during tropical storms and hurricanes.

To that end, the National Hurricane Center has been working on storm surge maps that will alert coastal areas about potential flooding and how high the water may get depending on proximity to the shore.

Those maps become operational this year and will be issued when the initial hurricane watch is made. In some cases it will be issued with the initial tropical storm watch.

The storm surge maps began an experimental phase in 2014.

A sample storm surge map for Fort Myers shows how far inland the water could reach from a tropical cyclone.
A sample storm surge map for Fort Myers shows how far inland the water could reach from a tropical cyclone.

“The problem is people prepare for wind and make assumptions about the strength of a hurricane based on wind,” said National Hurricane Center Director Richard Knabb in a presentation last year to Palm Beach County emergency managers. “We need to be thinking about all of the hazards.”

What would happen if Palm Beach County was hit by a Category 5 hurricane. 

Between 1963 and 2012, 49 percent of tropical cyclone deaths were storm surge related. Another 27 percent were attributed to rain accumulation.

Just 8 percent of deaths were from wind.

In 2005, Palm Beach County had just two evacuation zones. Now there are five based on the category of hurricane and how much water it will push ashore. Wind damage is less of a concern than storm surge.

“Wind gets the headlines, but it’s other hazards as well that we should be aware of,” said National Weather Service Warning Coordination Meteorologist Robert Molleda, who spoke at the same 2015 seminar as Knabb.