Tropical Cyclones • Coastal Hazards • Ocean Flooding
A hurricane does not have to bring the ocean over the coast as a giant breaking wave. It can raise the entire coastal water level first — then send waves, debris and currents across land that is normally dry.
Storm surge is the abnormal rise of coastal water generated mainly by strong storm winds pushing seawater toward land. Low atmospheric pressure adds a smaller contribution, while storm size, track, forward speed, continental-shelf depth, bays, estuaries, tide timing and local topography determine how severe the flooding becomes. This guide explains storm surge, storm tide, inundation, wave setup, run-up, coastal amplification, surge forecasting, historic disasters and why hurricane category alone is a poor measure of coastal flood risk.
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Storm Surge: Quick Facts
- Storm surge is an abnormal storm-driven rise in coastal water level.
- Strong onshore winds are usually the dominant surge-generating force.
- Low atmospheric pressure also raises water level, but usually contributes less than wind in major hurricane surge events.
- Storm tide is the storm surge combined with the astronomical tide.
- Inundation describes water flooding normally dry ground.
- Storm surge is not the same as wave height.
- Breaking waves can ride on top of an already elevated surge.
- Wave setup can raise nearshore water levels further.
- Wave run-up is the vertical reach of individual waves up a beach, dune or structure.
- Shallow continental shelves often amplify surge.
- Funnel-shaped bays and estuaries can concentrate water.
- Low-lying deltas are especially vulnerable.
- Storm size can matter as much as maximum wind speed.
- Hurricane category alone does not predict surge height.
- A small change in track can move the worst surge to a different coastline.
- High tide can worsen total storm-tide levels.
- Surge can penetrate rivers, bays, sounds and backwater areas.
- Rainfall and river flooding can combine with surge to produce compound flooding.
- Storm surge also occurs during extratropical and post-tropical storms.
- Storm surge is not a tsunami.
- Modern surge forecasting uses numerical models, ensembles, elevation data and uncertainty in storm track, size and intensity.
- The hurricane forecast cone does not show the full storm-surge hazard.
What Is Storm Surge?
Storm surge is an abnormal rise of coastal water generated by a storm above the water level that would otherwise be expected from the astronomical tide.
During a tropical cyclone, the main mechanism is strong wind blowing across the sea surface and transporting water toward the coast.
When the coastline prevents that water from moving farther forward, it piles up.
The result can be rapid flooding of:
- beaches;
- barrier islands;
- coastal roads;
- harbors;
- bays;
- estuaries;
- river mouths;
- low-lying neighborhoods;
- entire coastal plains.
Storm surge:
the storm-driven abnormal rise of water above the predicted astronomical tide.
How Does Storm Surge Form?
Storm surge develops through a combination of atmospheric forcing and coastal geometry.
1. Strong Winds Push the Ocean
Wind transfers momentum to the ocean surface.
Persistent onshore winds drive large quantities of water toward land.
2. Water Begins to Pile Up
As the storm approaches shallow coastal water, the transported seawater cannot simply continue moving forward beneath the land.
3. Coastal Geometry Concentrates the Water
Bays, estuaries, deltas, inlets and shallow shelves can amplify the rising water level.
4. Low Pressure Adds an Extra Rise
Lower atmospheric pressure near the storm center allows the sea surface to rise somewhat.
5. Waves Ride on Top
Destructive wind waves can then travel across the already elevated water surface and strike farther inland.
Wind vs Low Pressure: What Actually Creates Storm Surge?
Hurricanes are famous for extremely low central pressure, so it is tempting to imagine that the storm simply “sucks” the ocean upward.
That is not the main mechanism behind major surge.
Wind Stress Is Usually the Main Driver
Strong winds transfer momentum to the ocean and push water toward shore over a large area.
Low Pressure Adds a Secondary Contribution
Lower atmospheric pressure allows the ocean surface beneath the storm to rise somewhat.
This is often described using the inverse barometer effect.
Why the Distinction Matters
A very large cyclone with a broad field of strong onshore winds can create enormous surge even if its minimum central pressure is not record-breaking.
Storm Surge vs Storm Tide
These terms are closely related but they are not interchangeable.
Storm Surge
The abnormal rise in water produced by the storm.
Astronomical Tide
The normal rise and fall of sea level caused mainly by the gravitational influence of the Moon and Sun.
Storm Tide
The total water level created when the storm surge is superimposed on the astronomical tide.
In simple form:
Storm Tide ≈ Astronomical Tide + Storm Surge
Storm Surge Height vs Inundation Depth
Another important distinction is the difference between water level and water depth over land.
Storm Surge Height
Describes the storm-driven water-level anomaly relative to a reference water level.
Inundation
Describes flooding of normally dry land.
Inundation Depth
Describes how deep the water could become above the ground at a specific location.
Why This Matters for Residents
A statement such as “10 feet of storm surge” does not automatically mean every location experiences 10 feet of water above the floor.
Local ground elevation, barriers, channels, dunes, roads and coastal terrain all matter.
Storm Surge vs Waves, Wave Setup and Wave Run-Up
Storm surge is sometimes described as a “wall of water.”
That can be misleading.
Surge is primarily a broad elevation of coastal water level.
Waves then travel on top of that elevated sea.
| Process | Meaning |
|---|---|
| Storm Surge | Broad storm-driven rise in coastal water level. |
| Wind Waves | Surface waves generated by wind. |
| Wave Setup | Additional average rise in nearshore water level associated with breaking waves. |
| Wave Run-Up | Maximum uprush of individual waves on a beach, dune, cliff or structure. |
Why Historic Records Can Be Difficult
Older reports sometimes describe extreme marks on trees, hillsides or buildings without enough information to determine how much represented:
- mean storm surge;
- wave setup;
- individual wave run-up;
- debris impact marks.
This is one reason extreme historical claims such as the reported Cyclone Mahina water level require caution.
Why Shallow Continental Shelves Amplify Storm Surge
Bathymetry is the shape and depth of the seafloor.
It is one of the most important controls on coastal surge.
Shallow Shelf
Where shallow water extends far offshore, wind-driven water can pile up over a broad area before reaching the coast.
Steep Shelf
Where deep water lies close to shore, the same wind forcing may produce a different surge response.
Why the Gulf Coast Is Vulnerable
Large portions of the U.S. Gulf Coast combine:
- broad shallow shelves;
- low coastal elevation;
- bays and estuaries;
- barrier islands;
- extensive wetlands and river systems.
How Bays, Estuaries, Deltas and Barrier Islands Change Storm Surge
Coastlines are not straight walls.
Their geometry can redirect, trap or concentrate storm-driven water.
Funnel-Shaped Bays
Water entering a narrowing bay can become concentrated into a smaller area.
Estuaries
Surge can propagate inland through tidal channels and estuarine systems.
River Mouths
Ocean water moving upstream can oppose river discharge and worsen backwater flooding.
Deltas
Low elevation and dense waterways make major deltas particularly vulnerable.
Barrier Islands
Barrier islands may absorb some wave energy but can also be overtopped, breached or inundated.
Back Bays and Sounds
Water can enter enclosed or semi-enclosed coastal basins and remain elevated even as conditions change along the open coast.
What Controls Storm Surge Severity?
| Factor | Why It Matters |
|---|---|
| Wind speed | Stronger onshore winds generally push more water toward land. |
| Storm size | A broad wind field can transport water over a much larger ocean area. |
| Wind-field orientation | The direction of the strongest onshore winds determines where water is pushed most efficiently. |
| Track | Small track changes can move the highest surge to another coastline. |
| Angle of approach | Controls how the wind field intersects the coast and local bays. |
| Forward speed | Influences duration, timing and spatial distribution of water transport. |
| Central pressure | Low pressure contributes an additional water-level rise. |
| Continental shelf depth | Shallow shelves can strongly amplify surge. |
| Coastline shape | Bays, estuaries and river systems can funnel or trap water. |
| Astronomical tide | Changes the total storm-tide level. |
| Wave action | Breaking waves add setup and run-up on top of elevated water. |
| Ground elevation | Determines how far and how deeply water can inundate normally dry land. |
Storm Size vs Hurricane Category: Why Category Alone Misleads
The Saffir–Simpson Hurricane Wind Scale measures maximum sustained wind.
It does not directly measure:
- storm size;
- surge height;
- rainfall;
- wave height;
- forward speed;
- coastal vulnerability.
A Large Lower-Category Hurricane
Can generate a broad region of prolonged onshore wind and substantial coastal flooding.
A Compact Major Hurricane
May contain much stronger peak winds but a narrower wind field.
Why Emergency Managers Do Not Use Category Alone
Surge planning depends on storm-specific forecasts and local geography.
Why Storm Track and Landfall Angle Matter So Much
A storm does not produce equal surge on every side of its circulation.
Onshore vs Offshore Wind
The highest water generally occurs where strong winds push water toward the coast.
Nearby coastlines experiencing offshore winds may initially see lower water levels.
Small Track Changes Matter
A relatively small shift in the cyclone’s center can alter:
- which bay receives onshore wind;
- which side of a barrier island floods;
- which estuary channels water inland;
- where the highest inundation occurs.
Angle of Approach
A storm approaching perpendicular to one coastline can force water differently than one moving parallel to shore.
How Forward Speed Changes Storm Surge
Forward speed affects how long and where the wind pushes water toward the coast.
Slow Storms
Can prolong coastal water elevation and combine surge with extended rainfall and river flooding.
Fast Storms
Can move the strongest forcing quickly across a coastline, changing the timing and shape of the surge.
There Is No Universal “Slow Is Always Worse” Rule
Surge response depends on the combination of storm size, track, coastline and local basin geometry.
How High Tide and Low Tide Affect Storm Surge Flooding
Storm surge and astronomical tide are separate processes, but the coast experiences their combined water level.
Surge Near High Tide
Produces a higher storm tide than the same surge superimposed on low tide.
Surge Near Low Tide
The total water level can be somewhat lower — though still extremely dangerous during a major event.
Tides Change While the Storm Is Arriving
Because surge can last for hours, tidal timing can change during the event.
Compound Flooding: When Storm Surge Meets Rain and Rivers
Coastal disasters often involve more than one source of water.
Storm Surge From the Ocean
Seawater moves inland.
Extreme Rainfall From Above
Tropical cyclone rain creates urban and flash flooding.
River Flow From Inland
Rivers attempt to drain toward the sea.
Backwater Effects
Elevated coastal water can slow drainage through river mouths, canals and stormwater systems.
The Result
Water can accumulate from multiple directions simultaneously.
Storm Surge vs Tsunami vs Wind Waves
Storm surge and tsunami can both inundate coastlines, but their physical origins are fundamentally different.
| Feature | Storm Surge | Tsunami | Wind Waves |
|---|---|---|---|
| Main Cause | Persistent storm winds + smaller pressure contribution | Sudden displacement of water | Wind acting on ocean surface |
| Common Trigger | Hurricane, typhoon, cyclone or major extratropical storm | Earthquake, landslide or volcanic activity | Local or distant winds |
| Main Coastal Hazard | Prolonged elevated water and inundation | Long-wave flooding and strong currents | Breaking-wave impact and erosion |
| Duration | Often many hours | Multiple waves over hours | Varies with sea state |
Where Is Storm Surge Most Dangerous?
Any exposed coast can experience storm surge under the right conditions, but certain geographic settings repeatedly produce extreme disasters.
Bay of Bengal
One of the world’s most dangerous cyclone-surge regions because of its shallow northern waters, funnel-shaped geometry, low-lying deltas and dense coastal populations.
U.S. Gulf Coast
Broad shallow shelves, bays, river deltas, barrier islands and extensive lowlands create major surge vulnerability.
Philippines
Powerful western Pacific typhoons can produce destructive localized surge in bays and low coastal communities.
Caribbean
Islands and coastal embayments can experience severe surge and destructive waves, although local bathymetry varies dramatically.
River Deltas
Deltas are especially vulnerable because extremely low elevation intersects with rivers, tidal channels and densely populated land.
North Sea
Major extratropical storms can drive destructive surge into the shallow North Sea basin.
Storm Surge Is Not Limited to Hurricanes
Tropical cyclones produce some of the world’s most famous storm surges, but the phenomenon is not uniquely tropical.
Extratropical Cyclones
Large mid-latitude storms can generate prolonged strong winds across enormous ocean areas.
Post-Tropical Cyclones
A former hurricane does not lose its ability to generate surge simply because its meteorological classification changes.
Hybrid Systems
Large complex storms can retain damaging coastal wind fields even when their thermal structure is no longer purely tropical.
The Great North Sea Flood of 1953 remains a defining extratropical surge disaster.
How Is Storm Surge Forecast?
Storm-surge forecasting requires much more than knowing the predicted hurricane category.
Models must combine information about:
- forecast storm track;
- landfall location;
- angle of approach;
- maximum wind;
- complete wind-field size;
- storm asymmetry;
- forward speed;
- coastal bathymetry;
- shoreline geometry;
- bays and rivers;
- astronomical tides;
- ground elevation;
- forecast uncertainty.
Why Surge Forecasting Is Location-Specific
A track error of only a modest distance can place a bay on a completely different side of the storm’s wind field.
Why Forecasting Must Be Probabilistic
Meteorologists cannot know the exact future storm track, size and intensity.
Surge forecasts therefore use multiple possible storm scenarios rather than pretending one forecast path is exact.
The Forecast Cone Is Not a Surge Map
The tropical cyclone cone shows probable future positions of the storm center.
It does not show:
- the size of the hurricane;
- the wind footprint;
- the complete rain field;
- the complete storm-surge threat.
SLOSH and P-Surge: How Modern Surge Modeling Works
In the United States, one of the fundamental numerical tools used for hurricane surge analysis is SLOSH — Sea, Lake, and Overland Surges from Hurricanes.
What SLOSH Simulates
SLOSH models how water responds to a tropical cyclone’s:
- track;
- wind field;
- intensity;
- forward motion;
- interaction with coastal geography.
Why One Simulation Is Not Enough
The exact storm track and intensity will never be known perfectly in advance.
P-Surge
Probabilistic surge guidance combines large numbers of possible storm scenarios to account for realistic forecast uncertainty.
This allows forecasters to ask a more useful question:
How high could the water reasonably rise at this particular location given the range of plausible storm outcomes?
Potential Storm Surge Flooding Maps: What the Colors Actually Mean
Modern inundation maps are designed to answer one of the questions residents care about most:
How high could storm-surge water rise above normally dry ground where I live?
What These Maps Show
- areas where storm-surge flooding could occur;
- potential inundation depth above ground;
- the geographic spread of plausible flooding.
What Goes Into the Forecast
- storm track uncertainty;
- landfall location uncertainty;
- storm size;
- storm intensity;
- forward speed;
- coastal shape;
- seafloor slope;
- astronomical tides;
- ground elevation.
What the Map Does Not Automatically Include
Storm-surge inundation maps should not be interpreted as total flood-depth maps for every possible water source.
Separate hazards may include:
- rainfall flooding;
- river flooding;
- individual wave action;
- local drainage failure.
Storm Surge Watch vs Storm Surge Warning
In regions where dedicated storm-surge alerts are issued, a watch and a warning refer specifically to the danger of life-threatening coastal inundation.
| Alert | Meaning |
|---|---|
| Storm Surge Watch | Life-threatening inundation is possible, generally within about 48 hours. |
| Storm Surge Warning | Life-threatening inundation is expected or dangerous enough to warrant protective action, generally within about 36 hours. |
Why Surge Has Its Own Warning
A hurricane wind warning does not communicate the same hazard.
A location could face extreme inundation even if its wind exposure is not the greatest in the storm.
Rapid Intensification and Storm Surge Before Landfall
Rapid intensification can complicate surge forecasting when a tropical cyclone strengthens dramatically as it approaches the coast.
Stronger Winds
Can increase ocean forcing.
Changing Wind Field
Structural changes can alter where the strongest onshore winds occur.
Less Preparation Time
Communities may have to respond to a significantly stronger storm with little additional notice.
But RI Does Not Determine Surge Alone
Storm size, track, bathymetry and coastal geometry remain critical.
Historic Storm Surge Disasters and Benchmarks
The most important surge events are not necessarily the storms with the strongest winds.
They illustrate different ways the ocean, storm and coastline can combine into disaster.
| Event | Year | Region | Why It Matters |
|---|---|---|---|
| Cyclone Mahina | 1899 | Australia | Famous extreme historical water-level claim, but the often-cited value may include wave run-up and remains debated. |
| Galveston Hurricane | 1900 | United States | Defining U.S. storm-surge disaster and the deadliest U.S. natural disaster. |
| North Sea Flood | 1953 | Netherlands / UK / North Sea | Landmark extratropical surge disaster that transformed coastal defenses. |
| Bhola Cyclone | 1970 | Bangladesh | Defining low-lying delta surge catastrophe and one of history’s deadliest natural disasters. |
| Hurricane Katrina | 2005 | United States | Modern benchmark for extreme Gulf Coast surge and infrastructure failure. |
| Cyclone Nargis | 2008 | Myanmar | Devastating surge across the low-lying Irrawaddy Delta. |
| Hurricane Sandy | 2012 | United States | Classic example of how enormous storm size can produce a vast coastal flood footprint. |
| Typhoon Haiyan | 2013 | Philippines | Defining modern typhoon-surge catastrophe. |
| Hurricane Dorian | 2019 | Bahamas | Extreme inundation combined with exceptionally slow storm motion. |
| Hurricane Ian | 2022 | Florida | Modern U.S. benchmark for catastrophic coastal inundation and destructive wave action. |
Bhola Cyclone (1970): The Deadliest Storm-Surge Benchmark
The Bhola Cyclone struck the low-lying Ganges–Brahmaputra delta region in November 1970.
Why the Delta Was So Vulnerable
- extremely low elevation;
- densely populated islands;
- shallow northern Bay of Bengal;
- funnel-like coastal geometry;
- limited evacuation infrastructure at the time.
Why Bhola Matters
It demonstrates that storm-surge catastrophe is ultimately a combination of:
hazard × exposure × vulnerability.
Hurricane Katrina (2005): The Modern U.S. Storm-Surge Benchmark
Katrina produced catastrophic water levels along the northern Gulf Coast.
Why the Surge Was So Large
- large storm size;
- powerful wind field;
- long exposure over Gulf waters;
- shallow coastal shelf;
- vulnerable bays and lowlands.
Category at Landfall Does Not Tell the Whole Story
Katrina had weakened from its peak intensity before landfall, but its enormous circulation had already mobilized a vast volume of Gulf water.
This remains one of the clearest examples of why storm-surge risk cannot be inferred solely from the category number shown at landfall.
Typhoon Haiyan (2013): Extreme Surge in the Philippines
Typhoon Haiyan struck the central Philippines with exceptional intensity.
Tacloban and surrounding communities experienced catastrophic coastal inundation.
Why Haiyan Became a Global Surge Case Study
- extraordinary tropical cyclone intensity;
- powerful onshore winds;
- vulnerable coastal communities;
- local bay geometry;
- destructive waves riding over elevated water.
The event also demonstrated the difficulty of communicating the phrase storm surge to populations that may understand flood or tsunami terminology more intuitively. Learn more about tsunamis in the tsunami pillar.
Hurricane Sandy (2012): Why Storm Size Matters
Sandy became an extraordinarily large cyclone before reaching the northeastern United States.
Its vast wind field pushed water toward an enormous stretch of coastline.
The Sandy Lesson
Peak hurricane category is only one measure of a cyclone.
A very large storm can create:
- a huge wave field;
- a broad surge footprint;
- prolonged onshore winds;
- regional coastal flooding far from the storm center.
Hurricane Ian (2022): Modern Florida Surge Destruction
Ian produced catastrophic coastal flooding in southwest Florida, particularly around Fort Myers Beach and nearby barrier islands.
Why Ian Matters
It illustrates the dangerous combination of:
- major hurricane winds;
- rapid intensification before landfall;
- favorable surge geometry;
- low-lying coastal development;
- destructive waves on top of elevated water.
Storm Surge Myths vs Reality
| Myth | Reality |
|---|---|
| Storm surge is just a giant wave. | Surge is a broad storm-driven rise in coastal water level. Waves ride on top of it. |
| Storm surge is a hurricane tsunami. | Surge and tsunami have fundamentally different generating mechanisms. |
| Only Category 4 and 5 hurricanes produce deadly surge. | Storm size, track, shelf depth, coastline shape and tide can make lower-category storms extremely dangerous. |
| Low pressure sucks the ocean upward and creates the surge. | Low pressure contributes, but wind stress is generally the dominant driver of major surge. |
| If the hurricane eye misses my town, there is no surge risk. | Life-threatening surge can occur well away from the exact center track. |
| The forecast cone shows the storm-surge zone. | The cone represents uncertainty in the storm center’s future position, not the total hazard footprint. |
| Ten feet of surge means ten feet of water in every house. | Local inundation depth depends on ground elevation and local geography. |
| High tide causes storm surge. | The storm causes surge. The tide changes the total storm-tide water level. |
| Historic surge records are directly comparable. | Older measurements can include uncertainties involving run-up, setup and historical reporting methods. |
Storm Surge Safety: What Matters Most
Storm surge can become unsurvivable in exposed low-lying areas.
Know Your Evacuation Zone
Evacuation zones are generally based on modeled coastal flooding risk rather than only distance from the beach.
Follow Evacuation Orders Early
Waiting until floodwater is visible can be too late.
Do Not Use Hurricane Category as Your Evacuation Threshold
Local surge forecasts and emergency orders are more relevant.
Stay Away From Flooded Roads
Storm-surge water can:
- hide washed-out pavement;
- contain powerful currents;
- carry debris;
- contain sewage, fuel and chemicals;
- isolate escape routes.
Do Not Go to the Coast to Watch the Surge
Rising water can arrive rapidly, and destructive waves can travel across the surge far inland.
Which Legacy Hurricane Articles Should Redirect to Storm Surge Explained?
Redirect an old hurricane article here when its lasting informational value is primarily about coastal inundation caused by storm-driven seawater.
Redirect Here When the Article Focuses On:
- storm surge flooding;
- ocean water inundating streets or communities;
- coastal evacuation because of surge;
- storm-tide records;
- surge heights;
- water pushed inland by a hurricane or typhoon;
- coastal flooding at landfall;
- marinas or barrier islands overwhelmed by surge;
- historic cyclone-surge disasters;
- storm surge forecasts or maps;
- storm surge warnings;
- surge vs tsunami confusion.
Redirect Elsewhere When Another Phenomenon Dominates
| Dominant Topic | Best Destination |
|---|---|
| General hurricane / typhoon event |
Hurricanes & Tropical Cyclones Explained |
| Explosive strengthening before landfall |
Rapid Intensification Explained |
| Rainfall-driven inland flash flooding |
Flash Floods Explained |
| Hurricane-spawned tornadoes |
Tornadoes Explained |
| Two tropical cyclones interacting |
Fujiwhara Effect Explained |
| Actual tsunami | Redirect to the appropriate tsunami / ocean-wave pillar rather than here. |
Storm Surge Glossary
- Storm Surge
- Abnormal storm-driven rise in coastal water above the level expected from the astronomical tide.
- Storm Tide
- Total coastal water level created by the combination of astronomical tide and storm surge.
- Inundation
- Flooding of normally dry land by rising water.
- Inundation Depth
- Depth of floodwater above the ground at a specific location.
- Bathymetry
- Shape and depth of the seafloor.
- Continental Shelf
- Relatively shallow submerged margin extending outward from a continent before the seafloor steepens.
- Wind Stress
- Transfer of momentum from moving air to the ocean surface.
- Inverse Barometer Effect
- Sea-level response to atmospheric pressure changes, with lower pressure tending to allow higher local water level.
- Wave Setup
- Increase in mean nearshore water level associated with breaking waves.
- Wave Run-Up
- Maximum vertical extent reached by individual waves rushing up a shoreline or structure.
- Fetch
- Distance over water across which wind blows and transfers energy or momentum to the sea.
- SLOSH
- Sea, Lake, and Overland Surges from Hurricanes, a numerical model used to simulate storm-surge behavior.
- P-Surge
- Probabilistic storm-surge guidance that combines many plausible storm scenarios to represent forecast uncertainty.
- Storm Surge Watch
- Alert indicating the possibility of life-threatening inundation from storm-driven coastal water.
- Storm Surge Warning
- Alert indicating danger of life-threatening inundation from storm-driven coastal water.
- Compound Flooding
- Flooding caused or worsened by multiple water sources such as storm surge, extreme rainfall and river discharge.
Sources and Editorial Methodology
Storm-surge definitions, forecasts and modern benchmark values should be checked against official meteorological, oceanographic and disaster-agency sources.
Preferred Primary Sources
-
NOAA National Hurricane Center — Storm Surge
-
NOAA NHC — Potential Storm Surge Flooding Map
-
NOAA NHC — Storm Surge Products
-
NOAA NHC — SLOSH
-
NOAA Tides & Currents
-
NOAA
-
World Meteorological Organization
- National meteorological agencies and regional tropical cyclone warning centers
- Official post-storm tropical cyclone reports
- Peer-reviewed coastal engineering, oceanographic and storm-surge research
StrangeSounds Editorial Rules
- Use storm surge for the storm-driven water-level anomaly.
- Use storm tide for surge plus astronomical tide.
- Distinguish water level from inundation depth above ground.
- Distinguish surge from individual wave height.
- Distinguish wave setup from wave run-up.
- Do not describe storm surge as a tsunami.
- Do not imply central pressure is the main surge mechanism.
- Do not infer surge magnitude directly from Saffir–Simpson category.
- Always consider storm size and wind-field breadth.
- Always consider bathymetry and coastline geometry.
- Use caution when comparing historical surge-height claims with modern instrumented measurements.
- Do not present disputed Cyclone Mahina values as uncontested measured surge.
- Keep rainfall-driven flash flooding in Flash Floods Explained.
- Keep rapid-intensification physics in Rapid Intensification Explained.
- Keep general hurricane science in Hurricanes & Tropical Cyclones Explained.
- Redirect repetitive coastal-inundation hurricane news to this pillar.
Frequently Asked Questions About Storm Surge
What is storm surge?
Storm surge is an abnormal rise of coastal water generated by a storm above the level expected from the normal astronomical tide. Strong onshore winds are usually the dominant cause.
What causes storm surge during a hurricane?
Strong hurricane winds push seawater toward the coast. Low atmospheric pressure adds a smaller contribution, while bathymetry and coastal shape determine how strongly the water piles up.
Is storm surge caused mainly by low atmospheric pressure?
No. Low pressure contributes to elevated water levels, but wind stress pushing water toward land is generally the dominant cause of major hurricane storm surge.
What is the difference between storm surge and storm tide?
Storm surge is the storm-generated abnormal rise in water. Storm tide is the total water level after the astronomical tide is added to the surge.
What is storm surge inundation?
Inundation is flooding of normally dry ground by storm-surge water.
What does water above ground mean on a storm surge map?
It describes the potential depth of storm-surge flooding above the local land surface rather than water elevation relative to a tidal reference level.
Is storm surge the same as a giant wave?
No. Storm surge is a broad rise in coastal water level. Individual waves can ride on top of the surge and cause additional impact and run-up.
What is wave setup?
Wave setup is an additional rise in average nearshore water level caused by the effects of breaking waves.
What is wave run-up?
Wave run-up is the maximum vertical reach of individual waves as they rush up a beach, dune, coastline or structure.
Why do shallow continental shelves increase storm surge?
Broad shallow water allows storm-driven seawater to pile up more effectively as it approaches the coast.
Why do bays and estuaries amplify storm surge?
Narrowing coastal geometry can concentrate incoming water while channels and estuaries allow surge to travel inland.
Can a Category 1 or Category 2 hurricane cause deadly storm surge?
Yes. Storm size, wind-field breadth, track, shelf depth, coastline shape and tide timing can allow a lower-category storm to produce life-threatening surge.
Does a Category 5 hurricane always have the highest storm surge?
No. Category measures maximum sustained wind, while surge depends on many additional factors including storm size, track, bathymetry and coastal geometry.
Can storm surge happen far from the hurricane eye?
Yes. A large tropical cyclone can push water toward coastlines far from the exact center track.
Does high tide make storm surge worse?
High tide does not create storm surge, but it raises the starting water level and can therefore increase the total storm-tide level.
Can storm surge travel up rivers?
Yes. Surge can propagate into tidal rivers, estuaries, sounds and bays and can oppose river drainage, contributing to compound flooding.
What is compound flooding during a hurricane?
Compound flooding occurs when multiple water sources such as storm surge, extreme rainfall and river discharge overlap and worsen flooding together.
Is storm surge the same as a tsunami?
No. Storm surge is generated mainly by persistent storm winds, while tsunamis result from sudden displacement of a large volume of water, commonly by earthquakes, landslides or volcanic activity.
Can extratropical storms cause storm surge?
Yes. Large extratropical and post-tropical cyclones can generate major storm surge if they produce strong persistent winds toward vulnerable coastlines.
How is storm surge forecast?
Surge forecasts combine predicted storm track, wind field, size, intensity, forward speed and uncertainty with coastal bathymetry, shoreline geometry, astronomical tides and land elevation.
What is SLOSH?
SLOSH stands for Sea, Lake, and Overland Surges from Hurricanes. It is a numerical modeling system used to simulate storm-surge water levels in coastal areas.
What is P-Surge?
P-Surge is probabilistic storm-surge guidance that combines many possible storm scenarios to account for uncertainty in tropical cyclone track, intensity, size and forward motion.
What does the Potential Storm Surge Flooding Map show?
It shows where storm-surge flooding could occur and how high water could rise above normally dry ground, while incorporating uncertainty in the tropical cyclone forecast.
Does the hurricane forecast cone show storm surge?
No. The cone represents uncertainty in the future location of the tropical cyclone center. Storm-surge hazards can extend well outside it.
What is a storm surge watch?
A storm surge watch indicates the possibility of life-threatening inundation from rising coastal water, generally within about 48 hours in the U.S. warning system.
What is a storm surge warning?
A storm surge warning indicates danger of life-threatening inundation from rising coastal water, generally within about 36 hours in the U.S. warning system.
Can rapid intensification increase storm surge risk?
Yes. Rapid strengthening near the coast can increase wind forcing and worsen surge potential, although storm size, track, bathymetry and coastal geometry remain critical.
What was the deadliest storm surge disaster?
The 1970 Bhola Cyclone is widely recognized as the deadliest tropical cyclone disaster in recorded history, with catastrophic surge across the low-lying Bengal delta.
What was the highest storm surge ever recorded?
Cyclone Mahina in 1899 is often associated with an exceptionally high historical water-level claim near 13 metres, but the figure is debated and may include wave run-up rather than pure storm surge.
Why was Hurricane Katrina’s storm surge so destructive?
Katrina combined a very large wind field with powerful onshore winds, shallow Gulf Coast bathymetry and highly vulnerable bays and low-lying coastal terrain.
Why was Hurricane Sandy’s surge so large?
Sandy had an enormous wind field capable of pushing water toward a very broad section of coastline, demonstrating how storm size can be critical to surge risk.
Where should old hurricane storm-surge articles redirect?
Legacy articles whose main lasting value is storm-driven coastal inundation, surge heights, storm tide or seawater pushed inland should generally redirect to Storm Surge Explained.
