Storm surge, king tides, and coastal inundation¶

Storm surge is an abnormal, dome-like rise of ocean water pushed ashore by the violent winds of a hurricane, typhoon, tropical cyclone, or intense winter nor'easter / extratropical bomb cyclone. Combined with the normal astronomical tide, known altogether as the storm tide, a major storm surge can raise sea levels by 3 to 9+ meters (10 to 30+ feet) in a matter of hours, pushing walls of turbulent ocean water and battering waves 10 to 40 kilometers (6 to 25 miles) inland across low-lying marshes, bays, and river estuaries. When a storm surge coincides with a king tide (an exceptionally high perigean spring tide when the Moon is closest to Earth and aligned with the Sun), even a moderate Category 1 storm or winter gale can overtop seawalls and flood coastal cities. Historical mortality analysis by the United States National Hurricane Center (NHC), the World Meteorological Organization (WMO), and the UK Met Office proves that storm surge is the single deadliest hazard in coastal storms, accounting for roughly 50 percent of all direct tropical cyclone deaths. Because one cubic meter of seawater weighs 1,025 kilograms (\(1,728\text{ pounds per cubic yard}\)) and moves with unstoppable hydrodynamic momentum, survival in a mapped Storm Surge Evacuation Zone requires evacuating inland before high winds or pre-landfall water close barrier island bridges and causeways. For dedicated tropical cyclone preparation and wind survival, see our sister site hurricane.guide.

Fai nei loa¶

1. Su'e sa'o lau Sone Fa'ate'a o le Afā (Sone A, B, C, D, po'o E) ma tu'u i le taimi e fa'atonu ai lau sone e alu ese. Aua le fa'alagolago i lou manatuaga o afa ua mavae pe lolovaia lou auala i timuga mamafa. Siaki lau setete po'o le atunu'u fa'afanua fa'asao i le gataifale (Iloa Lou Sone i le US Atlantic ma Gulf of Mexico, po'o UK Environment Agency / European Coastal Flood Warning zones). Aveese sefulu kilomita (e le o le selau) i se fale malosi o lo'o i fafo i fafo o le faafanua o le sone o si'isi'i i luga o eleele maualuluga.
2. Cross barrier island bridges and low-lying coastal causeways BEFORE pre-landfall water rises or winds hit 63 km/h (39 mph). Do not wait for the eye of the storm to approach before driving off a barrier island or peninsula. Forerunner storm surge and astronomical high tides routinely flood low causeways 12 to 24 hours before the center of the storm makes landfall, and police close high-span coastal bridges as soon as sustained winds reach tropical-storm force (\(63\text{ to }72\text{ km/h}\) [\(39\text{ to }45\text{ mph}\)]) to keep vehicles from being blown off the bridge deck.
3. Read official NHC / Weather Service "Feet/Meters Above Ground Level (AGL)" surge forecasts literally. When the National Hurricane Center or your national meteorological agency forecasts "3 to 4.5 meters (10 to 15 feet) of inundation Above Ground Level (AGL)" for your coastline, that means ocean water will stand 3 to 4.5 meters deep on top of the dry dirt in your front yard, PLUS 1.5 to 3 meters (5 to 10 feet) of battering ocean waves riding on top of that surge dome, submerging a two-story house up to the roof peak.
4. Cut home electrical power at the main breaker panel and unplug EV/hybrid vehicles in salt-water flood zones before water enters. Unlike fresh rainwater, ocean seawater (\(3.5\%\) dissolved sodium chloride salt) is a powerful electrical conductor. When salty storm surge floods wall outlets, basement breaker panels, or the high-voltage lithium-ion battery pack of a parked Electric Vehicle (EV), e-bike, or golf cart, it causes violent saltwater short-circuits, toxic chlorine/hydrogen gas release, and unstoppable thermal runaway fires that burn buildings down even while surrounded by floodwater. Move EVs to high inland parking garages before the storm, and switch off your home's main circuit breaker before evacuating.
5. If trapped inside a flooding building by unexpected storm surge, climb to the highest floor, NEVER enter a closed attic without a roof exit, and call 911 / 112 / 999. If you missed the evacuation window and seawater is rising inside your home, move immediately to the second or third story. Never climb into an enclosed attic unless it has a walk-out dormer window, an openable skylight, or you carry a heavy axe, sledgehammer, or battery reciprocating saw to break through the roof decking; rising surge water traps victims against the inside of their roof rafters within minutes. Call your local emergency number (911 in the United States and Canada, 112 across the European Union, 999 in the United Kingdom, or see all numera fa'afuase'i) and stay on the downstream (leeward) interior side of the building away from wave impact.
6. Never drive or wade through coastal floodwater (even during sunny-day King Tides). Only 15 centimeters (6 inches) of rushing coastal water can knock you off your feet into rip-like return currents, and 30 to 60 centimeters (1 to 2 feet) of salty water will float your vehicle into a deep tidal canal while corroding your car's wiring harness, brake lines, and wheel bearings beyond repair.

Coastal inundation, storm surge, and king tide decision flowchart¶

Use this decision tree to act early when a Storm Surge Watch, Storm Surge Warning, or Coastal Flood Advisory is issued for your coastline.

flowchart TD
    Start["Coastal Inundation Threat:<br/>Storm Surge Watch/Warning, Hurricane/Nor'easter,<br/>or Perigean Spring 'King Tide'"] --> AlertType{"What type of coastal water event<br/>is forecast?"}

    AlertType -->|"1. STORM SURGE WARNING / HURRICANE EVACUATION<br/>Life-Threatening Inundation (>0.9 m / 3 ft AGL)<br/>within 36 Hours"| BarrierCheck{"Are you on a Barrier Island, Peninsula,<br/>or inside Mapped Evacuation Zone A / B / C?"}

    BarrierCheck -->|"YES: Inside Evacuation Zone"| EvacNow["EVACUATE IMMEDIATELY (12 to 36 hrs BEFORE landfall):<br/>1. Shut off Main Electrical Breaker & Main Gas/Propane Valve<br/>2. Move EVs, E-Bikes, & Cars to high inland ground (saltwater triggers EV fires)<br/>3. Cross causeways/bridges BEFORE forerunner surge or 63 km/h (39 mph) winds"]

    BarrierCheck -->|"NO: Outside Surge Zone, on High Ground"| ShelterInland["Shelter in Place away from trees & windows<br/>Review wind & power outage safety at hurricane.guide"]

    AlertType -->|"2. TRAPPED BY RISING STORM SURGE<br/>Water already covering roads & entering structure"| TrappedSurge["EMERGENCY VERTICAL SURVIVAL:<br/>1. Shut off main power breaker ONLY if standing on dry floor<br/>2. Climb to highest floor (2nd/3rd story) on leeward side away from breaking waves<br/>3. NEVER enter a closed attic without an axe/saw or walk-out roof window<br/>4. Put on Coast Guard PFD life jackets & call 911 / 112 / 999"]

    AlertType -->|"3. KING TIDE / SUNNY-DAY COASTAL FLOOD ADVISORY<br/>Minor-to-Moderate Tidal Flooding (0.3 to 0.9 m / 1 to 3 ft)"| KingTideAction["1. Ave'ese ta'avale paka mai auala maualalalo, uafu, & ta'avale i lalo o le 'ele'ele<br/>2. Aua ne'i alu atu i totonu o vai masima (fa'aleaga taofi, faavaa, & mea tau eletise)<br/>3. Aloese mai taligalu ma afu i le gataifale pe a sua sua (gau sneakers)"]

Comparing Storm Surge vs. Storm Tide vs. King Tides vs. Tsunami¶

Coastal residents often confuse these four ocean water hazards. Understanding the physics of each explains why a storm surge floods for hours across a wide coastline, whereas a king tide is a predictable astronomical peak and a tsunami is a seismic wave train.

Aisea e taoto ai le Vasega Matagi: O mea e 5 e faʻateleina ai le maualuga o afa¶

Aua ne'i fa'amasinoina le mata'utia o le afā i le Saffir-Simpson Hurricane Wind Scale na'o ia. E lima fa'afanua fa'afanua ma va'aiga fa'atele e mafai ona fa'atupuina ai se afa "vaivai" Vaega 1 po'o le Vaega 2 e maua mai ai se afā e sili atu le maualuga, ma le oti nai lo se afa laititi o le Vaega 4:

1. Bathymetry Papa'u i fafo¶

I vai loloto o le sami, o vai e tulei e le matagi e taamilo i lalo ma e le mafai ona faaputuputu maualuga. Peitaʻi, pe a tuleia e se afā le vai i luga o se faatafatafa o konetineta lautele, papaʻu, maseʻe malie, e pei o le Gulf of Mexico (Louisiana, Mississippi, Alabama, West Florida, Texas), le Bay of Bengal (Bangladesh ma Initia i Sasaʻe), o le ** North Sea** (Netherlands, Siamani, sasaʻe o Egelani), po o le ala i lalo o le Sami i Sasaʻe** Y. e fa'aputu i luga i totonu o se fa'ato'aga tele. - Faatusatusaga: O se afa o le Vaega 4 e taia ai pama Beach, Florida (lea e pa'u ifo ai le fata konetineta i le loloto o ni nai kilomita mai le matafaga) e ono tupu mai ai se \(2.5\text{ mita}\) (\(8\text{ foot}\)) si'isi'i, ae o le Category 3 afa e tutusa lelei lava le saoasaoa o le matagi e taia ai i le itu i saute sisifo o le Mississippi Fagaloa papa'u o le Mississippi6. i le }8.5\text{ mita}$ (\(20\text{ to }28\text{ foot}\)) afā afā**. (Gulf of Mexico)

2. Faga Fa'atusa, Fa'alogo, ma Vaitafe¶

A o'o mai se matagi malosi i totonu o se faga lautele po'o se gataifale e vaapiapi a'o alu atu i uta, e pei o le Tampa Bay, Chesapeake Bay, Galveston Bay, Long Island Sound / New York Harbor, Bristol Channel / Thames Estuary, po'o le Meghna River Estuary, o le vaiti o le matafaga e tosoina ai le vai o lo'o sau i totonu o se fa'aluega la'ititi (**) ave le vai mita maualuga i luga o le faga nai lo le matafaga tatala. Ae sili atu le leaga, o timuga tetele e tafe ifo i vaitafe mai uta e fetaui ma le galu o le sami e alu aʻe i luga o le gutu (lologa faʻafefiloi), lolovaia aai 30 i le 50 kilomita (20 i le 30 maila) i luga o le vaitafe.

3. Afā Radius (Savili Tele Tele) ma le Saosaoa i luma¶

A hurricane with a gigantic wind field (where tropical-storm-force winds extend \(400\text{ to }600\text{ kilometers}\) [\(250\text{ to }375\text{ miles}\)] from the center, like Hurricane Ike in 2008 or Hurricane Sandy in 2012) pushes an enormous volume of ocean water for days before landfall (integrated kinetic energy). Even if the storm's peak wind drops to Category 1 or 2 right before hitting the beach, that colossal moving mountain of water cannot stop and slams ashore with Category 4 or 5 surge heights.

4. Which Side of the Eye You Are On (The "Dirty Side" Quadrant)¶

Because cyclonic storms spin counterclockwise in the Northern Hemisphere (and clockwise in the Southern Hemisphere), the highest storm surge always strikes the coastline located in the Right-Front Quadrant in the Northern Hemisphere (to the right of the eye as viewed from the storm's forward path, or the Left-Front Quadrant in the Southern Hemisphere). On the opposite side of the eye, offshore winds initially blow water out of bays (exposing dry mudflats), only for that water to come roaring back in as a violent back-side slosh surge minutes after the eye passes.

5. Wave Runup and Destructive Hydrodynamic Force¶

A cubic meter of seawater weighs more than one metric ton (\(1,025\text{ kg}\) or \(2,260\text{ lb}\)). If a storm surge brings \(3\text{ meters}\) (\(10\text{ feet}\)) of stillwater depth onto a barrier island, breaking ocean waves \(2\text{ to }3\text{ meters}\) (\(6\text{ to }10\text{ feet}\)) high ride on top of that water straight into neighborhoods. While still floodwater merely wets a house, a breaking ocean wave moving at \(15\text{ to }25\text{ km/h}\) (\(10\text{ to }15\text{ mph}\)) delivers tens of thousands of kilograms of lateral impact force per square meter, shearing houses off wooden or concrete pilings and turning floating docks, boats, and propane tanks into multi-ton battering rams.

How to read official Storm Surge Maps and "Feet Above Ground Level (AGL)"¶

In the United States, the National Hurricane Center (NHC) uses the SLOSH model (Sea, Lake, and Overland Surges from Hurricanes) to generate two distinct types of maps that every coastal resident must know how to read:

Le lamatiaga o le afi o le vai masima faʻaonapo nei: Taavale eletise (EVs), uila uila, ma maa sola ile fale¶

O afā tetele talu ai nei (e aofia ai le Afa o Ian, Idalia, Helene, ma Milton i le Gulf of Mexico ma le US Southeast coast) na fa'aalia ai se lamatiaga mata'utia i le gataifale fa'aonaponei: po'o afi lithium-ion i tua o le osooso.

• Aisea e mu ai le vai masima i le EV ma le uila uila afi itula po o aso PE A MAUA le vai: Pe a goto le afā o le sami masima i lalo o le taavale Eletise (EV) o loo paka ai, taavale tapolo, scooter eletise, po o le uila uila, o le vai masima e tafe atu e tafe atu i tua atu o pa'u pa'u maa i totonu o le pusa eletise maualuga pe pulea maa. A o tafe ese le vai, o alalaupapa masima faʻafefeteina e faʻaleagaina ai paʻu kopa ma mafua ai le faʻaogaina o le eletise i totonu o sela, ma faʻaoso ai le vevela i le sili atu i le \(800^\circ\text{C}\) i le \(1,000^\circ\text{C}\) (\(1,500^\circ\text{F}\) i le \(1,800^}**texti{F}\) i le $1,800 i nisi taimi i le $1,800^) 2 vaiaso talu ona mavae le afa.
• 3 Tulafono Fa'atonuina o le Lithium-Ion Battery mo Sone Si'i Afā:
• A'o le'i alu ese: Ave ese uma taavale afi, hybrids, ma tapolo tapolo mai le sone o le afā agai i faletaavale maualuluga i uta, ma ave uma uila uila, e-scooters, ma mea faigaluega eletise lithium i luga po o oe. Aua ne'i tu'ua se EV po'o se uila afi e paka i totonu o se faletaavale i lalo o le fogafale i lalo o lou fale i se sone o afā (o le afi afi afi i totonu o le faletaavale i le fogafale i lalo o le a mu ai le fale maualuga i luga a'e pe a le mafai e ta'avale fuimu ona o'o atu i lou motu pa).
• If an EV, hybrid, or golf cart WAS submerged in saltwater: Do NOT attempt to start, charge, or drive the vehicle, and if possible, have a tow crew move it at least 15 meters (50 feet) outdoors away from all houses and other cars onto open pavement.
• Call 911 / 112 / 999 immediately if you hear popping, hissing, or whistling noises, smell a sweet chemical solvent odor, or see white/gray vapor coming from the bottom of a flood-damaged EV or home backup battery wall.

Safe post-surge return: Coastal scour holes, Vibrio vulnificus, and gas leaks¶

Returning to a barrier island or coastal neighborhood after a storm surge recedes carries severe physical and biological hazards:

1. Hidden Coastal Scour Holes and Undermined Pavement: Moving storm surge and ebb-surge currents carve deep underwater craters (scour holes \(1\text{ to }3\text{ meters}\) [\(3\text{ to }10\text{ feet}\)] deep) right around bridge abutments, seawalls, and house pilings, and wash out the sand underneath asphalt roads while leaving a thin crust of blacktop hanging in midair. Never drive onto coastal roads covered in sand over-wash until highway crews have inspected them, and probe ahead with a stick if walking through standing water.
2. (Gulf of Mexico)
3. Displaced Marine Wildlife and Floating Propane/Fuel Tanks: Retreating storm surge traps venomous snakes, fire ants (which form floating living rafts on top of floodwater), stingrays, and alligators inside garages and ground-floor rooms, while snapping underground propane and natural gas lines. If you smell rotten-egg gas odor or hear hissing upon returning, leave the property immediately without flipping any light switches.

Fesili e fai soo¶

Punavai ua siaki¶

• National Hurricane Center (NHC / NOAA, United States): Storm Surge Overview, SLOSH Model (Sea, Lake, and Overland Surges from Hurricanes) Technical Documentation, Potential Storm Surge Flooding Map (AGL), and Storm Surge Watch/Warning Definitions.
• National Ocean Service (NOS / NOAA, United States): What Is a King Tide (Perigean Spring Tide)? High Tide Flooding Outlooks and Sea Level Rise Technical Reports.
• World Meteorological Organization (WMO): Storm Surge Watch Scheme (SSWS) and Global Tropical Cyclone / Coastal Inundation Early Warning Guidelines.
• Met Office (United Kingdom) and Environment Agency (United Kingdom): UK Coastal Flood Forecasting, North Sea Storm Surge Warning System (lessons from the 1953 and 2013 North Sea surges), and Severe Flood Warning Protocols.
• Federal Emergency Management Agency (FEMA, United States) and National Fire Protection Association (NFPA, United States): Coastal Construction Manual (FEMA P-55) and Saltwater Submersion Lithium-Ion Electric Vehicle (EV) Thermal Runaway Fire Advisories.

Taiala fa'atatau¶

• Afā, afa, ma afa
• Lologa: sauniuni, aveese, ma toe foi saogalemu
• Tsunamis: natural warning signs and high-ground evacuation
• Suavai ma vai o le sami fa'afuase'i
• Ta'avale i totonu o le vai: sola ese le ta'avale