Monday, May 28, 2018

Compound Flood Threat from Surge and Rain along Florida Panhandle Today

Key Message
While Alberto’s highest storm surge levels so far have been observed between 2-3 feet in Cedar Key and Apalachicola, a rapid water level rise and higher storm surge levels are possible near and east of the landfall location this afternoon. The area threatened by sudden storm surge inundation includes Panama City and Panama City Beach, where winds should rapidly shift from offshore to onshore as Alberto approaches landfall. Prolonged onshore winds in this region near and after the time of landfall will keep storm surge levels elevated and inhibit the drainage of heavy rainfall, increasing the flood threat.

Subtropical Storm Alberto has maintained a maximum sustained wind speed of approximately 65 mph overnight, as the center of circulation has slowed down and followed more of a northwest track. As of 400AM CDT the center of circulation was approximately 125 miles south of Destin, Florida. On its current path, the center of Alberto’s circulation should pass south of Panama City, with a landfall between Pensacola and Panama City this afternoon.

The center of Alberto's circulation is visible south of the Destin/ Panama City region in this 2 km resolution infrared satellite imagery from the University of Wisconsin/ CIMSS Tropical Cyclones Group

The highest coastal flood observations have been offset to the east, where onshore winds have generated storm surge between 2-3 ft. The NOAA tide gauge at Apalachicola observed a storm surge of 2.3 ft at 100AM EDT. As high tide approached, storm surge levels dropped below 2 ft. The NOAA tide gauge at Cedar Key reported a storm surge of 2.68 ft at 912PM EDT. Fortunately, this was around the time of low tide.

As of 600AM EDT, Alberto's storm surge has exceeded 2 ft at Apalachicola and Cedar Key, Florida.

Total storm tide levels (storm surge + tide) at Cedar Key reached 2.62 ft at 1:30AM EDT and 2.58 ft at Apalachicola at 5:36AM EDT on Mon May 27. Coastal flood levels likely reached even higher levels between these two gauges, as southerly winds in this region efficiently pile up storm surge near the northern coast of Apalachee Bay, near St Marks.

The U-Surge project has identified high water marks from 35 hurricanes and tropical storms at Cedar Key since 1880. Alberto’s storm tide ranks 29th on the list. The high watermark in Apalachicola ranks 32nd among the 41 observed in events in U-Surge since 1900.

Subtropical Storm Alberto has generated a 2.62-ft storm tide at Cedar Key, Florida, which ranks 29th out of high watermarks from 35 hurricanes and tropical storms since 1880, according to the U-Surge Project.

Storm surge levels have remained less than two feet above normal in the Panama City area, as winds in the region have been blowing offshore at less than 20 mph overnight. However, a rapid water level rise is possible along this section of coast around the time of landfall, as winds shift from offshore to onshore.

The National Hurricane Center has issued a storm surge watch for Panama City, Panama City Beach, Mexico Beach, Lynn Haven and Bayou George, as the potential exists for 2-4 feet of storm surge inundation ABOVE GROUND LEVEL according to a statement from the National Weather Service in Tallahassee.

While storm surge has not yet overwashed the beach in Panama City, Florida, Alberto threatens this region with a rapid water-level rise closer to the time of landfall this afternoon. Image: WPMI/ WLUK-TV Fox 11.

Flash flooding is a real threat, particularly east of Alberto's track, where persistent onshore winds will generate a prolonged storm surge, which will inhibit the drainage of heavy rainfall. The National Hurricane Center forecasts more than 4 inches of rain to fall across portions of the Florida Panhandle and Alabama.

The National Hurricane Center forecasts more than 4 inches of rain to fall across portions of the Florida Panhandle and Alabama. Where prolonged onshore winds keep storm surge levels elevated east of Alberto's track, drainage of heavy rainfall will be inhibited, leading to greater flood threat.

Although Alberto is not forecast to reach hurricane strength before making landfall, the notion of a May hurricane striking the Florida Panhandle and Apalachee Bay region takes our thoughts back to Hurricane “Amanda” of 1863, the only May hurricane to make landfall in the U.S. The BAMS paper published by Chenoweth and Mock on this storm is a great read on this Memorial Day, as it covers both long-forgotten hurricane history and U.S. military history. The authors named the hurricane “Amanda” after a Union ship that was driven ashore during the Civil War.

I find Amanda a fitting name, as our current naming convention is alphabetical and a tropical cyclone forming in the Gulf of Mexico in May will likely start with the letter "A" (unless it's the second named storm).

Looking beyond the Gulf Coast, a devastating flash flood tore through Ellicott City, Maryland, yesterday, for the second time in two years. Floodwaters threatened both life and property following torrential rains.

Sunday, October 8, 2017

Nate's Storm Surge Exceeds 6 ft in SE Mississippi

Hurricane Nate's storm surge has exceeded 6 ft in SE Mississippi, according to a NOAA tide gauge at Pascagoula. Video footage on social media depicts multiple feet of storm surge inundating casinos in Biloxi.

Other tide gauges in the region reported maximum storm surge levels reaching 4-6 feet, including Shell Beach, Louisiana, Bay Waveland Yacht Club, Mississippi, and Mobile State Docks along the Mobile, Alabama, waterfront.

Nate made landfall as a category-1 hurricane twice. The first landfall occurred in southeast Louisiana, near the mouth of the Mississippi River, and the second landfall occurred near Biloxi, Mississippi. The 400AM Central Time advisory from the National Hurricane Center downgrades Nate to a tropical storm, but beware of continued strong squalls to the east of the center of circulation.

Storm surge levels should drop through the morning along the northern Gulf Coast.

Saturday, October 7, 2017

Hurricane Nate Storm Surge Update

As of 900PM Central Time, Hurricane Nate has generated a widespread 2-4 ft storm surge along the Gulf Coast. Peak surge levels have now exceeded 4 ft at Shell Beach, Louisiana, and continue to rise in this location.

Expect maximum storm surge levels to reach 4-7 ft east of the Mississippi River in SE Louisiana, as well as the Mississippi Coast.

These storm surge levels do NOT include normal astronomical tides, which are peaking this weekend in the region due to the full moon. These king tides are among the highest tides of the year, and are not included in these storm surge observations.

Therefore, give a buffer for additional flooding because tides would normally be unusually high even if there wasn't a hurricane in the Gulf.

NHC Wildly Over-predicts Nate's Storm Surge Potential

As Hurricane Nate races towards the northern Gulf Coast, the National Hurricane Center's (NHC) 1PM (Central Time) advisory predicts maximum storm surge levels to reach 7-11 feet from the Mouth of the Mississippi River east to the Mississippi/ Alabama border, 6-9 feet along the Alabama Coast, and 4-6 feet for the Western Florida Panhandle, including Pensacola, as well as the area west of the Mississippi River, to Morgan City, Louisiana.

Visible satellite image of Hurricane Nate as of 11:15AM Central Time on Sat Oct 7, 2017

Although Nate is forecast to make landfall as a category-2 hurricane, these estimates are wildly over-estimated for several reasons:

1) Nate is RACING to the coast at an incredible 25 mph. This is more than twice the forward speed at which hurricanes typically approach the coast in this part of the world. Strong onshore winds need ample time to push water towards the coast, and Nate's rapid forward speed means it will make landfall before it has the chance to generate a substantial storm surge.

2) Nate is strengthening as it approaches the coast. I was lead author on a paper published three years ago that found storm surge correlates better with pre-landfall wind speeds than wind speeds at landfall, with the optimal correlation occurring 18 hours before landfall. So even if Nate makes landfall as a category-2 hurricane, 18 hours before landfall wind speeds were around 80-85 mph, making it an "average" category-1 hurricane when the time was most important for storm surge generation.

3) Nate's wind field is small. As of the 1PM Central Time advisory, hurricane-force winds extended only 35 miles from the center of circulation and tropical storm force winds extended 125 miles (see graphic below). 

Nate's small wind field will keep it from generating a massive storm surge. This graphic from the NHC depicts hurricane-force winds as red and tropical storm force winds as light orange, as of 10AM Central Time on Sat Oct 7.

Compare that with Hurricane Ike (2008), which approached the Upper Texas Coast as a high-end category-2 hurricane with hurricane-force winds extending 120 miles and tropical storm force winds extending 275 miles from the center of circulation, enabling Ike to generate a massive storm surge.

4) Nate's wind field has consistently been asymmetric, or offset, during it's journey through the Yucatan Channel and into the Southern Gulf of Mexico. Strongest winds have been offset to the east of the center. Given the predicted track, maximum sustained winds should stay east of the Louisiana Delta, and I cannot understand the rational for predicting 4-6 feet of storm surge west of the Mississippi River. The Mississippi River Delta does a good job of protecting points west, like Grand Isle and Morgan City, from storm surge even in a well-organized system- it is very unlikely that Nate will generate a storm surge higher than 3 ft in these areas.

Marine Weather and Climate runs the U-Surge project, which essentially serves as the U.S. storm surge database. I have personally been constructing storm surge databases for the past 10 years, and, based on that work, I would like to offer a storm surge forecast of my own, from a data-driven perspective.

Here is a comparison of my Marine Weather and Climate storm surge forecast compared to the NHC forecast, from west to east:

Much thanks to the NHC for their hard work and for rolling out improved products in recent years. I like what they do and value their work.

I believe in the power of having multiple voices/ forecasts as a big storm approaches. This helps the public discern levels of certainty for a given hazard, like rainfall, wind or storm surge. If all forecasters provide the same message, certainty is higher than if different messages are heard.

I realize I will probably get my "hand slapped" for publicly disagreeing with the NHC on Nate's storm surge potential. In the days leading up to Harvey I got my hand slapped for not sticking with "one consistent message" when I published a blog post titled, "Harvey's Compound Rain/ Surge Flooding Could be Catastrophic and Underestimated- Especially along the Houston-Galveston Corridor", 36 hours before all hell broke loose in Houston.

However, Harvey was unbelievably catastrophic in my neck of the woods, and I have no regrets whatsoever for speaking my mind. For every hate message, I received hundreds of messages from people thanking me for speaking clearly and truthfully, and many thanking me for helping them make "life-saving decisions". Harvey taught me to speak my mind and not care what people think.

I do realize the NHC errs on the side of over-estimating storm surge potential to encourage people to evacuate and take precautions, but the down side to this is that it lowers public confidence when forecasts are consistently more extreme than the reality on the ground.

I believe the best approach is to predict hazards as accurately as possible and communicate this as clearly as possible with the public. Most people are smart and they will do what is necessary to protect their families and communities when given clear, accurate predictions.

For questions or comments on Nate's storm surge, you can reach me at:



Tuesday, September 12, 2017

Four Surges in One - Perspective on Irma's Wild Coastal Flooding

Although Hurricane Irma made landfall in the Lower Florida Keys as a category-4 hurricane, the massive storm generated wild coastal flooding patterns throughout the Florida peninsula, Georgia and South Carolina. Here's a recap on Irma's storm surge.

Peak Surge Levels

The map below depicts Irma's peak storm surge levels, with storm surge representing the difference in observed and predicted water levels based on normal astronomical tides. The highest observed storm surge levels exceeded 6 feet in places near the Florida/ Georgia border, like Fernandina Beach and Mayport, while water levels in a wider area from east-central Florida through South Carolina, as well as portions of southwest Florida, observed surge levels exceeding 4 feet.

Map of maximum storm surge data. Map created by Dr. Hal Needham (Marine Weather and Climate/ U-Surge), data provided by NOAA Tides and Currents.

As people are just returning to the worst-hit areas of the Florida Keys and southwest Florida, maximum storm surge areas are still being reported.  The table below provides the mapped data in tabular form.

Storm surge observations for Hurricane Irma
Effective Tue Sep 12 at 06:00AM Eastern Time

Storm Surge (water level above normal astronomical tides)

NOAA Tides and Currents Tide Gauges (preliminary water levels)

Fernandina Beach, FL:      7.75 ft

Mayport, FL:                       6.42 ft
Fort Pulaski, GA:               5.63 ft
Naples, FL:                         5.14 ft

Charleston, SC:                 4.87 ft
Trident Pier, FL:                 4.43 ft
Fort Myers, FL:                  4.25 ft
Virginia Key, FL:                3.91 ft
Key West, FL:                    3.30 ft
Old Port Tampa, FL:          3.17 ft

Springmaid Pier, SC:         3.04 ft
Vaca Key, FL:                     2.76 ft
Cedar Key, FL:                   2.50 ft
​Lake Worth, FL:                 2.23 ft
St. Petersburg, FL:            1.96 ft    

Irma's large size and shore-parallel track through southwest Florida, enabled the storm to generate four distinct storm surge events in different regions. Here's a summary below:

Florida Keys

Irma made landfall at Cudjoe Key, in the Lower Florida Keys, as a category-4 hurricane with maximum sustained winds of 130 mph on Sun Sep 10 at approximately 9:10AM Eastern Time.

NOAA tide gauges to the west (Key West) and east (Vaca Key) Irma remained more-or-less operational throughout the storm's passage, although the gauge at Key West has been reporting data intermittently. Surge levels at both sites increased substantially after Irma's eye passed and winds changed direction. As Irma approached, prolonged winds were blowing from east-to west across the Keys, but winds suddenly reversed from west-to-east after the eye passage. Maximum surge levels at both Key West and Vaca Key remained less than 4 feet.

Storm surge levels are highly localized, particularly in island chains, where two locations just several miles apart border water in different directions. For example, the NOAA tide gauge at Key West is located near the western end of the island, making it most susceptible to storm surge generated by a strong west wind.

NOAA's Key West tide gauge is located near the western end of the island, making it most susceptible to strong winds approaching the island from the west.

Based on Irma's track, the highest storm surge levels in the Keys, would have likely occurred near Cudjoe Key, Big Pine Key and Marathon. Initial rumors of a 15-foot storm tide (storm surge + tide) circulating social media remain unverified and were likely exaggerated. However, numerous images of sail boats swept onto the Overseas Highway (Hwy 1) provide evidence of a powerful storm surge that swept through the islands.

While spending time on Monday evening on social media groups focused on connecting locals from the Florida Keys, I noticed that numerous posts suggested a peak storm surge in the range of 5-6 feet at Cudjoe Key. However, this information was still speculative, as evacuees were not allowed back into the region yet and information from the Keys to the outside world was limited, often relying on satellite phones.

Although storm surge levels at Key West remained below 4 ft, the force of water pounding over the seawall was powerful enough to peel the paint off the famous "Southernmost Point" monument. 

Keep in mind that along island chains, storm surge values are extremely localized. Water displaced from a distance can pass between islands, but where a hurricane's eyewall is engaged on an island, surge levels will quickly spike, sometimes reaching levels twice as high as areas just 10-15 miles away.

Authorities are letting residents back into the Lower and Middle Keys today, so we should know more about the wind and storm surge impacts soon.

Video posted by Anthony Paul Davis shows storm surge flooding in Marathon, Florida.

Florida West Coast

Florida's West Coast observed the most unusual storm surge patterns, as Irma moved from south to north, approximately following a shore-parallel track. Due to counterclockwise winds around hurricanes in the Northern Hemisphere, substantial "negative" storm surges, when water is pushed away from the coast, occur when hurricanes take shore-parallel tracks and have a large body of water to the left of their forward path.

This occurs because prolonged winds of increasing intensity blow offshore along the coast, while the storm cannot draw any new water to replace the displaced water because strong winds are blowing offshore.

Numerous images of extensive mudflats emerged on Sunday afternoon in places like Tampa Bay. In some cases, humans were able to rescue marine animals, like dolphins and manatee, that were stranded by the receding water.

Marine animals, like manatee, became stranded as Irma pushed water away from Florida's west coast on Sunday, producing negative storm surges. Image: Michael Sechler/ Facebook.

People should use caution in such situations, as rapid changes in wind direction as the eye approaches, can lead to the water rushing back into the bay, along with additional water from an onshore storm surge.

The hydrograph below shows a "negative" storm surge of approximately 5.3 ft was observed at Old Port Tampa on Sunday afternoon, followed by rapid water level rises leading to a storm surge that exceeded 3 ft by Monday. Loss of data near the peak "negative" storm surge may indicate that the water level was too low for the gauge to record.

Hydrograph for Old Port Tampa depicts a substantial "negative" storm surge followed by a "positive" storm surge. Red = observed water level, blue = normal astronomical tide, and the difference is the storm surge.

Negative storm surges of this magnitude are somewhat rare but not unprecedented. The U-Surge Project, which provides more than 9,000 storm surge observations for the United States since 1880, places Irma's negative storm surge at Old Port Tampa in the top-5 all-time recorded negative storm surges. Three of the top five events occurred at Tampa.

Notable "Negative" Surges in the U-Surge Database

Year        Storm Name       Water Level (ft)          Datum              Location
1926        Great Miami         -10.30                       MSL                Mobile, AL
1910        Unnamed              -8.00                        Unknown        Tampa, FL
1926        Great Miami         -6.00                         MLT                Tampa, FL
1943        Unnamed              -5.70                         NAT                Galveston, TX
2017        Irma                      -5.32                         NAT                Old Port Tampa

Datums: MSL = Mean Sea Level; MLT = Mean Low Tide; NAT = Normal Astronomical Tide

The Great Miami Hurricane of 1926 generated the most extreme negative storm surge level on record, as the storm took a shore-parallel track along the northern Gulf coast, which generated powerful offshore winds near Mobile, Alabama, reducing water levels in Mobile Bay by more than 10 feet. This storm did not take a shore-parallel track along Florida's west coast, but Tampa stayed north of the storm's track, enabling powerful offshore winds to persist through the most intense part of the storm.

The Great Miami Hurricane of 1926, generated a "negative" storm surge of 10.30 ft at Mobile, Alabama, and 6.0 ft at Tampa. Powerful offshore winds pushed water away from the coast in both cases. 

Although negative storm surges may seem benign, and appear harmless compared to positive storm surges, such events can have negative impacts as well. Rapid water loss in marinas can leave fiberglass boats on hard surfaces as powerful winds push them around. Of greater impact to the general public would be loss of water for critical cooling processes at large facilities, like power plants. Given the susceptibility of negative storm surges at Tampa, local planners and utility operators should review potential impacts from negative surges in the region.

Storm surge flooding was evident in Everglades City during reconnaissance on Mon Sep 11.

Storm surge levels in southwest Florida, near Naples and Fort Myers, are not as severe as forecast, as Irma tracked farther inland than feared on Sunday morning.

Nonetheless, the eye remained offshore while passing the community of Everglades City, and reports are just surfacing about extensive storm surge flooding in this region. Everglades City likely observed the highest storm surge level on Florida's west coast.

Southeast Florida

Southeast Florida remained on Irma's "strong side" from Friday through much of Sunday, enabling storm surge to gradually increase over a several day period. At Virginia Key, near Miami, storm surge levels unfortunately peaked around midday Sunday, near the time of high tide. This enabled the NOAA tide gauge at this site to report a maximum storm tide (storm surge + tide) level of 3.88 ft above NAVD88 datum.

The U-Surge Project launched a Miami website as Irma approached, enabling us to compare Irma's maximum water level with 27 observed events since 1880. Irma's storm tide ranked 10th all-time and was the highest reported saltwater level since Hurricane Wilma in 2005. This water level was high enough to flood much of Miami's financial district with flood water on Sunday. 

Time series of observed storm tide events at Miami, Florida, from 1880-2017 (138 years). Irma's storm tide ranked 10th all-time and highest since Hurricane Wilma in 2005. 

Approximately 10-12 inches of sea-level rise in the Miami area over the past century enabled Irma to flood thousands of additional properties, even though the peak storm surge remained around 4 feet. In fact, if Irma hit one century ago, the maximum storm tide in Miami would have been around 2.88 ft, which would have ranked it 12th all-time (instead of 10th), as total water levels would have been lower than the storm tides from Hurricane Donna (1960) at 3.74 ft and Hurricane King (1950) at 3.67 ft.

NE Florida, Georgia, South Carolina

As of Tuesday morning, Irma's highest credible storm surge observations have been reported from northeast Florida through South Carolina, including the Georgia Coast. Fernandina Beach, Florida, near the Georgia border, leads the pack with a 7.48-ft storm surge observation.

Due to high tidal ranges in this region, storm surge observations only tell part of the story. The worst flood impacts usually occur near the time of high tide.

As this region stayed on Irma's "strong" side throughout the entire event, a prolonged storm surge in this region ensured moderate storm surge levels would persist through multiple high-tide cycles.

Although storm surge levels at Fort Pulaski, Georgia, near Savannah, peaked at more than 5 feet near the time of low tide, before dawn on Monday, persistent onshore winds kept storm surge levels elevated through the day. Astronomical tide levels rose faster than storm surge retreated on Monday morning, enabling peak water levels to exceed 12 ft above Mean Lower Low Water, which generated the second-highest water level on record at the gauge in an 82-year period, barely missing the maximum level set last October by Hurricane Matthew, according to Jill Gambill, with Georgia Sea Grant.

The Savannah River reached extreme levels on Monday, overflowing its banks and inundating portions of downtown Savannah. 

On their Category 6 blog post yesterday evening, Jeff Masters and Bob Henson provided excellent insights on storm surge observations in Georgia and northeast Florida, including a record water-level set in Jacksonville. Irma's persistent storm surge, heavy rainfall runoff and high astronomical tides converged in this region to provide widespread flooding on Monday.

Both Jacksonville and Savannah were victims of compound flooding, when prolonged onshore winds elevate storm surge levels for multiple high tide cycles and impede the drainage of heavy inland rainfalls.

This is my last update on Hurricane Irma's storm surge. Feel free to contact me with questions or interview requests at:

Let's hope the Gulf Coast and Southeast States can dry out in the next couple of weeks and that Hurricane Jose stays out to sea!

Take care and stay safe, everyone!


Sunday, September 10, 2017

Update on Hurricane Irma's Storm Surge

Storm Surge Levels May Have Reached 15 ft in the Lower Keys

An early, but unverified, report from Cudjoe Key, FL, appears to show a 15-foot storm surge. This would have been a likely location for peak storm surge in the Keys, as Irma tracked just west of here, keeping places like Cudjoe Key and Marathon on the "strong" side of the storm.

Tweet from Chris Suchan (@ChrisSuchanKCTV) appears to show a storm surge approaching 15 ft in Cudjoe Key. Water levels have not yet been verified.

Irma passed east of Key West, generating powerful east winds as the eye approached. This pushed water away from the tide gauge, which sits at the western end of the island. As Irma tracked north, "wrap around" winds on the back side of the eye, produced strong west winds and increased surge levels on Key West. See tide gauge graph below, where the blue line is normal tide level and red is observed. The difference is the storm surge. 

Water levels at Key West rose more rapidly after Irma made its closest approach and winds shifted to the west. Blue = astronomical tides, red = observed water level, difference = storm surge

Irma Closing in on Naples/ Marco Island Area

Irma is approaching the Naples/ Marco Island area. Unfortunately, it appears that the center of the eye will pass just west of these locations, enabling the eastern eyewall, the strongest part of the storm, to make a direct hit.

Throughout the storm, winds have been blowing from the east with increasing intensity in this region. Expect a sudden shift of wind direction from the south, rapid intensification of winds and a catastrophic storm surge to rapidly push into these areas over the next three hours.

If you stayed in Naples or Marco Island, the next three hours are all about survival. It's actually better for the eye of the storm to pass directly over your house than for it to track west of your house and leave you in the eastern eyewall.

If you must escape a flooded ground floor by going into an attic, make sure you take some water and an axe or something to break your way through the roof. Winds will persist from the west, keeping surge/ flood levels elevated for some time.

Irma's eyewall is approaching the Naples/ Marco Island area now. Follow excellent radar feeds on Wundergound's WunderMap.

Where did all the water go?
Strong east winds have pushed water away from the coast to the north of Irma's center. This has caused "negative" surges in places like Fort Myers and Tampa, as water levels have rapidly dropped, exposing extensive mud flats.

Beware! This water will all rush back, with additional storm surge on top, as soon as the winds die down in the eye or change direction immediately after the eye passes. Expect wild changes in water levels all along the western Florida coast over the next 24 hours, with local changes occurring most rapidly near Irma's eye.

Click once to help your city!
Stuck inside and wish you could help your city in some way? You can! The U-Flood Project launched FloodMap to enable people like you to map flooded streets in real time.

It's so easy:
1) Go to this website:
2) Click on the image of your city
3) Click on a street to mark it as flooded

Even if you just mark the street in front of your house, the effort from thousands of users will generate a real-time map of flooding in your city. This provides crucial information to emergency services and enables the public to follow Irma's flooding.

Downtown Miami is starting to flood, according to this real-time map of flooded streets. Just click on a street to mark it as flooded.

Game of inches (or miles)

As Irma does a tightrope walk up the Florida Gulf Coast, a change of track by just a few miles will make a world of difference.

Worst case scenario is Irma's eye staying just offshore and the eastern eyewall engaging your community.

This will especially make a dramatic difference in storm surge levels.

Where the eyewall is generating powerful onshore winds, expect rapid and catastrophic storm surge to overwhelm the coast.