Thursday, October 6, 2016

Matthew to Strike Florida with Storm Surge after Devastating Cuba and the Bahamas

Snapshot: Hurricane Matthew struck Cuba and the Bahamas with devastating storm surges on Tuesday and Wednesday. Florida is next, particularly in Central and Northeast Florida, including Melbourne, Cocoa Beach, Daytona Beach and Jacksonville, although uncertainty in the track forecast will impact storm surge levels. Highest surge will likely occur from extreme northeast Florida through Georgia coast. Expect severe surge damage in this region. If Matthew makes landfall near or south of Palm Beach County, it would likely produce highest water levels there since 1947 (69 years).


Cuba and the Bahamas

Hurricane Matthew devastated Cuba on Tuesday with a substantial storm surge near Baracoa. Although the city was located on Matthew's "back side," this slow moving, intense hurricane generated prolonged northeast winds of at least category-3 strength, enabling water to flow into coastal communities along the northeast coast of Cuba.

Rapid storm surge and intense onshore winds destroyed much of Baracoa, Cuba. Source:https://twitter.com/MikeTheiss.

Media coming out of Baracoa portrays widespread debris, as waters surged through the streets and intense winds inflicted damage.

The area around the city contains a few features that enhance storm surge, most notably, bowl-shaped bays that help increase water levels during a storm surge event.



Several concave-shaped bays helped increase water levels near the city of Baracoa, Cuba on Tuesday. 

Baracoa is located near the eastern tip of Cuba, on the north shore. Matthew produced intense "wrap-around winds" that impacted this area for many hours.

Matthew's storm surge was even more catastrophic in the Bahamas. This island archipelago contains broad reefs, containing shallow water that are ideal for generating storm surge. Hurricanes produce storm surge more efficiently in areas with shallow water, because the water piles up and cannot be redistributed by deeper currents.

Matthew is still pounding the Bahamas, as the slow-moving hurricane is now impacting the central and northern islands. In all, Matthew will have lashed these islands for more than 48 hours, a grim statistic considering hurricanes create higher surges when strong winds blow over water for longer periods of time.

The National Hurricane Center predicts that Matthew will still generate a storm surge of 10 to 15 feet (3 to 5 m) in the central and northern Bahamas today, and this range fits well in historical context. Last year, Hurricane Joaquin slowly moved through the Bahamas as a category-4 hurricane, generating storm surge as high as 15 ft (4.57 m) on Rum Cay, San Salvador, Crooked Island and Acklins.


Central and Northeast Florida Coast


Matthew is forecast to maintain major hurricane strength (at least category-3 winds), as it approaches the Central Florida coast. The 5AM NHC advisory provides a best track that brings Matthew's center of circulation along, or very close to the coastline, from near Jupiter through Melbourne, Daytona Beach and near Jacksonville Beach.



This is a shore-parallel track, which impacts wind and storm surge severity in several ways. Slight deviations to such tracks make substantial differences, as a track change of 30 miles (50 km) may mean the difference between a landfalling hurricane and one in which the most intense wind stays out to sea.

For this reason, I am not posting maps right now of analog hurricanes to avoid miscommunication. Hurricane Matthew will likely take a unique track that does not match precisely with historic storms, so storm surge patterns could be quite different. 

A second factor of shore-parallel tracks is that if a hurricane in the Northern Hemisphere is tracking from south to north along the east coast of a landmass, coastal locations will observe prolonged onshore winds that continue increasing until the eyewall arrives. Such long-duration onshore winds enhance storm surge levels.

Also, keep in mind that a shore-parallel track means that hundreds of miles of coastline are observing strong onshore winds. In contrast, a shore-perpendicular track would mean that strong onshore winds are confined to a smaller area.




The National Hurricane Center predicts the following water levels related with coastal flooding:


The water could reach the following heights above ground if the peak
surge occurs at the time of high tide...

Sebastian Inlet to Savannah River, including portions of the St.
Johns River...6 to 9 ft
Savannah River to South Santee River...3 to 5 ft
Deerfield Beach to Sebastian Inlet...3 to 5 ft
Virginia Key to Deerfield Beach...1 to 3 ft




Keep in mind, these are water levels above the ground, and storm surge often flows like a river. A surge of only two feet above the ground can inflict substantial damage, particularly if it is fast-flowing.

If Matthew's track follows a path slightly west of the NHC best track forecast, which would still be within the cone of uncertainty, it would make landfall near or just south of Palm Beach/ West Palm Beach. This region has had a string of good luck related to hurricanes, as Andrew (1992) struck south of here and Frances (2004) and Jeanne (2004) made landfall just north of Palm Beach city.

The two hurricanes in 2004 inflicted wind damage on the area, but the strongest winds blew offshore, minimizing storm surge levels. Frances produced a higher water level than Jeanne, with storm tides (storm surge + tide) levels reaching 6.3 ft (above NAVD88 datum) at Lake Worth tide gauge, in southern Palm Beach County.

This was the highest water level since 1947, when a powerful hurricane inflicted an 11-ft storm tide at Palm Beach. However, it is interesting to note that storm tides reaching at least 7 ft (2.13 m) were observed five times in the 40-year period of 1926-1965, with water levels reaching that level in 1926, 1949 and 1965, and exceeding it in 1928 and 1947.

Yet, for the past 69 years, storm tides have not reached that 7 ft (2.13 m) threshold again.

Time series of storm tides since 1900 at Palm Beach/ West Palm Beach. Available at www.u-surge.net.

I get concerned when I see numerous coastal floods in a historic record at a specific location, especially when such activity is followed by decades of relative tranquility. And that is what we see in the coastal flooding record for Palm Beach County.

I was so concerned about this that I launched the Palm Beach/ West Palm Beach metro area as the second community in the U-Surge Project, an endeavor to create the first comprehensive storm surge histories for 50 U.S. cities. I have removed the password protection on the Palm Beach/ West Palm Beach website for Hurricane Matthew, so anyone can view the site at this link: http://www.u-surge.net/palm-beach-west-palm-beach.html.

The page contains storm surge data, graphics, maps and multi-media. I also published an article on the site back on March 30, 2016, titled, "Why Palm Beach County Residents be Unprepared for Storm Surge Flooding."

Kimberly Miller, a journalist at the Palm Beach Post, worked with me to provide some local context to this issue in an article she published on April 1, 2016, titled, "Palm Beach County residents aren't prepared for biggest hurricane threat, expert says." Kimberly does an excellent job reporting on weather, climate and environmental issues, and I appreciated her perspective on this urgent topic.

As Hurricane Matthew bears down on this area, it appears that this research and writing was a great investment of time.



I have created a Hurricane Matthew webpage on the U-Surge site, which will enable us to keep up with storm surge monitoring and forecasts. I am plotting the maximum water level at Lake Worth Tide Gauge, just south of Palm Beach, on the graph of historical storm surges for the Palm Beach area, so we can place Matthew's storm surge in historical context.

Water levels this morning are still near normal astronomical tides, but expect the water to rise rapidly steadily through the day, and more rapidly this evening. Peak water levels in this area will likely occur after midnight tonight, when high tide and Matthew's closest approach are forecast to occur.


Regardless of Matthew's precise track, highest storm surge levels should occur north of Sebastian Inlet, which would include the cities of Melbourne, Cocoa Beach, Daytona Beach, Jacksonville, and the entire Georgia Coast (according to NHC advisory).

People in this region should expect a swift and powerful storm surge could destroy many structures along the coast on Friday and early Saturday. I post to the blog again tomorrow morning to discuss storm surge potential and historical context in this region (Northeast Florida, Georgia and Southern South Carolina).

Feel free to send me an email at hal"at"marineweatherandclimate.com if you have any thoughts or questions.

Stay safe, everyone!

-Hurricane Hal








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