Storm Surge Pushes into Charleston

Good morning everyone. After prolific blogging/ analysis this week I stepped away from the computer for around 18 hours to come down to Corpus Christi, Texas, and give a seminar at Harte Research Institute yesterday afternoon. We had a great turnout for a Friday afternoon talk on storm surge.

I'm just getting back to Hurricane Matthew now. It looks as if Matthew has tracked along the coast, as predicted. The northern eyewall was moving into Charleston around 1-2 hours ago, pushing a substantial storm surge.

Storm surge moving into Charleston this morning. Photo: @MelisEgan on Twitter

Are you affected by Matthew's storm surge? What is/ was it like?

Please place a comment on this blog post and tell us more.

I have not yet completed the U-Surge pages for Charleston and Savannah, which would place Matthew's surge in historical context.  I hope to complete these soon. 

Email or place a comment on this blog if you have comments or questions. Email: hal@marineweatherandclimate.com

Our thoughts are with those in coastal SC facing the brunt of Matthew right now.

THANK YOU for all the encouraging feedback I received yesterday!

-HH

The "Protected Coast" is Now the Most Dangerous Place of All

Snapshot: Many people consider the stretch of coast from northeast Florida through Southern South Carolina, including the entire coast of Georgia, as a "protected coast," immune from coastal hazards. Hurricane Matthew now threatens to slam this coastline with a storm surge more severe than anywhere else the storm has impacted. The "Protected Coast" is now the most dangerous place of all, as Matthew turns back the time and delivers a knock-out punch similar to the vicious hurricanes that struck this region in the late 1800s.

The "Protected Coast"

Many people consider the stretch of coast from northeast Florida through Southern South Carolina, including the entire coast of Georgia, as a "protected coast," immune from coastal hazards.

And with good reason.

The coastal profile in this region bends quite smoothly in a concave fashion, creating a broad basin of water that extends west from the Gulf Stream Current. This concave coast does indeed appear protected compared to more vulnerable areas to the north and south.

Many people consider the concave-shaped coastline from northeast Florida to southwest South Carolina, including the entire coast of Georgia, a "protected coast," immune to coastal hazards.

To the north, the coastline of North Carolina juts out into the Atlantic, exposing it to more hurricane strikes. To the south, the Florida Peninsula reaches out towards Cuba, extending itself into a hurricane highway that wants to connect the Atlantic to the Gulf of Mexico. But in between these areas is a protected enclave, enabling folks in Savannah to sleep well at night, not too worried about the next hurricane strike.

Hurricane history from the past decades seems to support this notion. Hurricane Hugo slammed South Carolina north of Charleston in 1989, but the area south of Charleston survived with little damage. Hurricane Andrew struck South Florida in 1992, far away from this region, and even hurricanes Frances and Jeanne in 2004 inflicted little damage, as they passed to the south.

Longer-term scientific analysis of hurricane strikes also supports the idea that this region is protected. For example, when Dr. Barry Keim and others at Louisiana State University conducted a comprehensive analysis of hurricane strikes from Texas to Maine, they found that only two hurricanes since 1901 impacted St. Simons Island, Georgia. Neither of these storms were major hurricanes, defined as category-3 or higher storms.

In this same period, Cape Hatteras. North Carolina, observed 21 hurricane and three major hurricane strikes. Miami and Palm Beach, Florida, both observed 21 hurricane strikes and six major hurricane strikes in this same timeframe. 

Keim and others from Louisiana State University published a study that included return period analysis of hurricane strikes. This graphic shows the number of years that pass, on average, between major hurricane (red), hurricane (orange) and tropical storm (light green) strikes. In the 105-year period study, St. Simeon Island (city 26) observed two hurricanes, meaning the return frequency of a hurricane strike is approximately 52 years.

Likewise, from Cocoa Beach, Florida, to Tybee Island, Georgia, on the border with South Carolina, only one (Jacksonville Beach) of five cities had observed a major hurricane since 1901. So this study showed a strong geography to hurricane risk, with observed hurricane data providing a clear picture of drastically reduced risk along this concave-shaped coast.

As a graduate student in climatology at LSU, I cut my teeth on this and other data-driven studies conducted by Dr. Keim and other scientists. Such research fascinated me, I saw great value in it, and I endeavored to do similar analyses for storm surge. Indeed, this is a project I am still undertaking today.

Throughout the years of data-driven analysis, one of the lessons I have learned is the value of looking "beyond" the period of analysis to see what's on the other side. Every climate study needs to start somewhere, and this study by Keim and others starts in 1901. However, when we look just before that start date, into the late 1800s, we see an interesting pattern emerge along our Protected Coast.

(And this is of no fault to Keim and others....my own storm surge research began with the year 1880, and I was sometimes asked if it bothered me that I just missed out on the 1875 Indianola Hurricane that struck Texas. But if I moved my start date up to 1870, then I would just miss another major storm...it's a never ending cycle.)

The Hyperactive Period of the Late 1800s

The late 1800s was a time of hyperactive hurricane activity along the Protected Coast. Catastrophic hurricanes frequently lashed this region with vicious winds and deadly storm surges.

Perhaps the statistic that best sums up the hyperactivity of this time is an obscure fact I found hiding in the back of a book in a Charleston library. Between 1888 and 1898, eight different hurricanes passed within 75 nautical miles of Hilton Head, South Carolina. That's eight hurricanes in 11 years.

The years 1893, 1894 and 1898 all observed two hurricanes in this area.

However, in the 117-year period extending from 1899 to 2015, only seven hurricanes passed within that area. This means the Hilton Head area, in southern South Carolina, near the Georgia border, observed more hurricane activity during an 11-year period in the late 1800s, than it did in the following 117 years.

The graphic below (a pic I snapped with my camera) shows this pattern. It reveals five hurricanes from 1899 to 1993, but hurricanes Irene (1999) and Charley (2004) must be added to the list, because they passed within 75 nautical miles of Hilton Head.

Graphic of tropical cyclones passing within 75 nautical miles of Hilton Head, South Carolina. From: Smith, David J., 1994: Hurricane Risk, Hilton Head, South Carolina, Climate Report G-18, 20 pp.

Not only did many hurricanes strike this region in the late 1800s, the most severe storms inflicted catastrophic storm surges. The three most severe examples are the back-to-back hurricanes in  1893 and the Great Hurricane of 1898.

Back-to-Back Hurricanes in 1893

On August 27, 1893, the Great Sea Island Storm generated a 12-foot storm tide (surge + waves) at Savannah Beach, Georgia, and water levels reaching 18.2 feet from combined storm tide and waves.

This storm devastated the region from Savannah to central South Carolina, inflicting many fatalities.

The Great Sea Island Storm of 1893 was the first of two hurricanes to devastate Charleston in that active tropical cyclone season. 

Here is a quote on the storm from NOAA Technical Memorandum NWS Hydro-19:

This major hurricane, which originated in the Cape Verde Islands, reached the Georgia coast on August 27. It was accompanied by a very high storm tide which submerged the islands along the Georgia and South Carolina coasts. Between 2,000 and 2,500 people lost their lives on the coastal islands and in the lowland between Tybee Island~ Ga. and Charleston, S.C. Property damage along the coast was estimated at $10 million. Damage in Savannah was placed at more than $1 million. Nearly every building on Tybee Island was damaged and the railroad to the island was wrecked. The highest tide known to have occurred in the county was estimated to have a range of 17.0 to 19.5 ft msl at Savannah Beach [18.2 ft. given in reference [7]].

Shockingly, another powerful hurricane struck the region on October 13, generating a storm tide of 14 feet at Pawley's Island and 12 feet at Charleston. 

The Great Sea Island Storm of 1893 generated storm tide and waves reaching 18.2 feet along the Georgia Coast and killed 1,000-2,000 people. Map Source: Unisys Corporation

A second major hurricane struck the region two months after the Great Sea Islands Storm, generating storm tides of 12-14 feet along the South Carolina Coast. Map Source: Unisys Corporation

The Great Hurricane of 1898

The Great Hurricane of 1898 was even more severe in terms of maximum storm surge levels along the Georgia Coast. This vicious storm generated a storm surge of 16 ft (4.88 m) at Brunswick, and a storm tide of 18 ft (5.49 m) at Sapels Lighthouse. The storm killed 179 people along the Georgia coast.

The Great Hurricane of 1898 generated a 16-ft (4.88 m) storm surge at Brunswick, Georgia, completely devastating the harbor.

This stretch of coastline is less vulnerable to hurricane strikes than areas to the north and south, however, these three powerful hurricanes in the late 1800s show us that when a hurricane does strike this area, the storm surge can be catastrophic.

Ironically, some properties of storm surge are counterintuitive. Places that are usually the safest, like harbors, bays and inlets, generate the highest storm surges. This is also true for concave-shaped coastlines, like the Protected Coast. The shape of this region and the relatively shallow bathymetry (offshore water depth), efficiently pile up storm surge, but first we need a powerful hurricane tracking in from the southeast, like Matthew. This region is particularly vulnerable to storms like Matthew, as the coastline is open to the east, the very direction from which Matthew is blowing powerful winds for several days.

The coastline of northeast Florida, Georgia and southern South Carolina efficiently builds up storm surge due to its concave shape, relatively shallow offshore water depth and openness to strong east winds, as a hurricane approaches from the south. Graphic: Hal Needham

The efficiency of the Protected Coast for enhancing surge levels was already seen yesterday evening, while Hurricane Matthew was centered off the coast of South Florida. Even though Matthew was located closer to Palm Beach than Jacksonville, storm surge levels in extreme northeast Florida (Fernandina Beach) and Georgia (Fort Pulaski) were already higher than any other NOAA Tides and Currents tide gauge.

This should cause concern, as Matthew would not make landfall in this region for more than 24 more hours after these data were collected (see map below).

Storm surge levels along the Southeast U.S. Coast at 6:00PM EDT on Thu Oct 6.
Water levels: NOAA Tides and Currents; Map: Hal Needham

The National Hurricane Center storm surge forecast has remained consistent since yesterday evening, with peak water levels of 7-11 feet above ground level predicted from northeast Florida to Southern South Carolina. See map below that I created yesterday evening (forecast is the same now).

Indeed, the Protected Coast is now the most dangerous place of all, and we can only hope that coastal populations in this region have heeded the mandatory evacuation and removed themselves from harm's way.

One of the take home lessons from Hurricane Matthew is that we should take the time to read deep into the history of coastal hazards. We should be concerned when we see hyperactive hurricane history in a location like Georgia and southern South Carolina, even if the past decades have been relatively quiet.

If you have questions or comments, feel free to email me at: hal@marineweatherandclimate.com.

Thanks for taking time to read my posts!

-Hurricane Hal

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

Hurricane Matthew Strikes Haiti, Eyes Cuba and Bahamas

Snapshot: Hurricane Matthew's storm surge impacts will be relatively minor in Haiti and Cuba, but catastrophic in the Bahamas.

Hurricane Matthew made landfall as a category-4 hurricane with sustained winds of 145 mph along the Tiburon Peninsula in south Haiti this morning. Matthew is forecast to emerge into open water around the western end of the Gulf of Gonave and make landfall or a very close approach to the southeastern tip of Cuba, in Guantanamo Province, before threatening the Bahamas on Wednesday.

Hurricane Matthew's eye is visible as it makes landfall in south Haiti on Tue Oct 4. This RBTOP color enhanced color image from NOAA shows that south Haiti will have several more hours of hurricane impacts.

Fortunately, from a storm surge perspective, the areas impacted in both Haiti and Cuba are not susceptible to large storm surges. Deep bathymetry, or offshore water depth, in these areas reduces storm surge potential, because displaced water can redistribute itself where the bathymetry is deep. The water depth just 5 miles (8 km) offshore in these areas of Haiti and Cuba exceeds 3,000 feet (914 m) deep in many areas.

Bathymetry is shallower in Port-au-Prince Bay, and storm surges could threaten areas like Cite Soleil, a densely-populated area within the Port-au-Prince metropolitan area, if not for the orientation of the bay. This region would require intense, sustained northwest winds to generate a large storm surge near Port-au-Prince, but a hurricane could only do this if it was centered inland, due to the counter-clockwise rotation around hurricanes in the Northern Hemisphere. Even wrap-around winds on the back side of Matthew should not create a dangerous storm surge near Port-au-Prince, and any coastal flooding impacts in Haiti will be overshadowed by severe impacts from heavy rainfall runoff and mudslides.

The National Hurricane Center forecasts Matthew to maintain status as a major hurricane, while striking Haiti and Cuba, and then tracking slowly through the Bahamas.

The National Hurricane Center predicted storm surge levels of 7 to 10 feet along the south coast of Haiti, and this should occur within a narrow area near the eastern eyewall at landfall. Although this is a relatively low storm surge level for a category-4 hurricane, we should expect extraordinary waves in this region. Areas with deep bathymetry observe high waves because the energy of incoming waves is not broken until very close to shore. The difference between storm surge and waves is that a wave is a rise in water that may only last several seconds, whereas a storm surge is a dome of water that can last anywhere from 30 minutes to several days.

Deep bathymetry offshore usually translates to high mountains on land, which is the case in both Haiti and eastern Cuba. The orographic influence of these mountains enhances the lifting of air, increasing rainfall potential and exacerbating the impacts of heavy rain, as steep slopes experience rapid runoff and mudslides. As with most hurricanes affecting this region, Matthew’s greatest impact on both Haiti and Cuba will be flash flooding and mud slides.

In 1963, Hurricane Flora impacted this region, causing morethan 7,000 deaths, mostly in Cuba and Haiti. Flash flooding caused majority of these deaths.

Hurricane Flora inflicted at least 7,000 deaths in 1963, mostly in Haiti and Cuba.

The National Hurricane Center predicts storm surge levels could reach 7 to 11 feet along the southern coast of Cuba, east of Cabo Cruz. This region is similar to Haiti in regards to deep offshore water depths and mountainous terrain on land.

Cuba has experienced catastrophic storm surges before, but not in this region of the country. A hurricane in 1932 generated a 21.3-ft (6.5-m)storm surge that killed 2,870 people at Santa Cruz del Sur in Camaguey province. A 25-mile (40-km) wide shelf in this region exacerbates storm surge by providing a pool of shallow water that can be easily displaced. However, in southeastern Cuba, where Matthew’s impact will be greatest, hurricanes inflict most damage from heavy rainfall runoff and mudslides.

Hurricane Matthew will impact southeastern Cuba, an area with deep offshore water. The 1932 hurricane inflicted a catastrophic storm surge at Santa Cruz del Sur, a location with a pool of shallow water to the south.

BAHAMAS

The Bahamas are more vulnerable to storm surge than Cuba and Haiti, and storm surge will likely be the major hazard that Matthew inflicts upon this country. The National Hurricane Center predicts a storm surge that will reach 10 to 15 feet (3.1 – 4.6 m).

Many areas in this archipelago contain broad reefs that provide large pools of shallow water for hurricanes to displace and inflict storm surge damage. The impacts of these surges are often severe, sea water can overwash small islands, completely inundating them with salt. Such surges often destroy fresh water and food supplies, as saline soils can take years to lose high salt content.

The reef at Long Cay, Crooked Island and Acklins Island is opened to the southwest with a fetch, or straight line distance of at least 20 miles (32 km). Hurricane Joaquin inflicted a 15 ft (4.57 m) storm surge last year in this area.

Of particular concern is the possibility that Matthew will track far enough east to produce a large storm surge on Crooked Island, Acklins Island and Long Cay. Hurricane Joaquin generated a devastating 15-ft (4.57-m) storm surge in this area just last October, taking advantage of a shallow reef that is open to the southwest. A second large storm surge in two years would have grave impacts for this region.

Hurricane Joaquin generated a massive storm surge in the Bahamas last October, as seen from the inland displacement of these boats. Photo: AP/ Tim Auven.

Whether Matthew produces a comparable storm surge on these three islands remains to be seen, but one thing looks likely: Matthew will inflict catastrophic storm surge damage in the Bahamas, as it is forecast to slowly move through the Bahamas as a major hurricane.