Storm surge watch or warning: when to prepare and when to leave

The water hazard

Storm surge is more than a high tide or a wind category

The National Hurricane Center defines storm surge as an abnormal rise in water generated by a storm above the predicted astronomical tide. Storm tide is the combination of surge and the normal tide. Waves can ride on top of that elevated water and add destructive force along the coast.

• Surge is driven mainly by strong onshore wind, but storm size, intensity, speed, angle of approach, coastal shape, water depth, bays, rivers, canals, and barrier islands all influence it.
• The hurricane category describes maximum sustained wind. It does not directly describe the surge expected at your address.
• A large tropical storm or lower-category hurricane can still produce life-threatening surge in a vulnerable location.
• Heavy rain and river flooding are separate hazards that can occur at the same time and can extend far inland.

Use the exact product name

Outlooks, forecasts, watches, and warnings are not interchangeable

Each product answers a different question. Read the product title, issue time, affected area, valid period, and official instructions. A cone or wind warning alone does not tell you the complete water risk.

Tropical Weather Outlook

An outlook identifies areas where a tropical cyclone could develop. It is an early planning signal, not a local surge forecast, watch, warning, or evacuation order.

Storm surge forecast

NHC surge products estimate where flooding could occur and how high water could reach above normally dry ground. They change as the storm forecast and uncertainty change.

Storm Surge Watch

A watch means life-threatening inundation is possible somewhere in the specified area, generally within 48 hours. Use that time to finish preparations and be ready to leave.

Storm Surge Warning

A warning means there is a danger of life-threatening inundation somewhere in the specified area, generally within 36 hours. Follow evacuation and other local instructions promptly.

NHC may issue a surge watch or warning earlier when tropical-storm-force winds could reduce the time available to evacuate. An area can also be included because surrounding flooding could isolate it.

Read height correctly

The flooding map shows water above ground—not above sea level

When issued for an active cyclone, the NHC Potential Storm Surge Flooding Map shows areas where surge flooding could occur and the height water could reach above normally dry ground. The colors do not show rainfall totals, wave height, or the storm's wind category.

The NHC describes the map as a reasonable worst-case planning scenario for individual locations. There remains about a 1-in-10 chance that the water at a particular location could exceed the mapped value. Roads shown on the basemap are for orientation; the map does not promise that any road will remain open.

Evacuation decisions

Your local evacuation zone matters more than the forecast cone

The hurricane forecast cone shows the probable track of the cyclone's center. It does not show the full wind field, the limits of surge, rainfall flooding, tornadoes, or who must evacuate. Local officials use hazard information together with roads, bridges, shelters, and community conditions when issuing evacuation instructions.

1. Know your local evacuation zone before a storm threatens.
2. Know more than one route and where you could stay inland.
3. Include medicines, mobility needs, children, older adults, and pets in the plan.
4. Keep fuel, chargers, documents, and essential supplies ready during the watch stage.
5. Leave when local officials tell your zone to evacuate; do not wait to see water rising.

Evacuation zones and flood-insurance maps serve different purposes. Being outside a mapped insurance flood zone does not cancel an evacuation order. Use the evacuation information from your state, county, city, or tribal authority for the current storm.

Before returning

Wait for officials to say the route and neighborhood are safe

Water may remain after the wind weakens or the cyclone moves inland. Roads, bridges, utilities, buildings, and drainage systems can be damaged even where the surface appears calm.

• Do not drive through water, around barricades, or onto a closed bridge.
• Stay away from downed lines, damaged buildings, floodwater, and unstable shorelines.
• Do not return until local authorities open your area and route.
• Continue checking official alerts because rain and river flooding can persist after surge recedes.
• Call 911 for an immediate life-threatening emergency.