King tides and sunny-day flooding
King tides are extra-high tides around the new and full moon. They can push seawater onto low roads, yards and parking lots even on a sunny day. Check the tide forecast, don't drive or walk through saltwater on the road, and remember homeowners insurance usually doesn't cover flooding.
Information may be delayed or incomplete. Always verify with official sources and follow local officials.
What is a king tide?
“A King Tide is a non-scientific term people often use to describe exceptionally high tides.”NOAA National Ocean Service, What is a king tide?
NOAA says tides run higher than normal when the moon is new or full, and higher still when the moon is closest to Earth or during certain seasons. NOAA also says shifts in winds and ocean currents can push high tide flooding onto streets even on sunny days.
Why streets flood on sunny days
“High tide flooding is the overflow or excess accumulation of water that covers typically dry coastal land and occurs during high tides.”NOAA Tides & Currents, High Tide Flooding
NOAA says high tide flooding, also called sunny day or nuisance flooding, can close roads, back up storm drains and shut businesses for a while. Because of rising seas, sinking land and the loss of natural barriers, NOAA says it now happens twice as often in U.S. coastal communities as it did 20 years ago (NOAA: high tide flooding).
NOAA uses these rough national levels, measured above the average high tide:
- Minor: about 1.8 feet. Disruptive: storm drains back up and roads close.
- Moderate: about 2.8 feet. Can damage homes and businesses.
- Major: about 3.9 feet. Often destructive, and evacuations may be needed.
Your street may flood at a different level. In the Florida Keys, NWS Key West says the limestone under the islands is porous, so seawater can seep up through the ground and flood areas away from the shore (NWS Key West).
When to watch for it
NWS Key West says the highest tides there usually come in the fall and early winter and peak around new and full moons, when the Earth, sun and moon line up. NOAA Tides & Currents also publishes a yearly high tide flooding outlook for each tide gauge, running May through April (NOAA Tides & Currents).
- Find your gauge. Look up the nearest tide gauge on NOAA Tides & Currents. NWS Baltimore/Washington suggests learning the water level that floods your street and planning what you'll do at each level (NWS: Tidal flood).
- Check the high tide time. This kind of flooding happens during high tides (NOAA), so look up when high tide is before you head out.
- Get alerts more than one way. NWS Baltimore/Washington notes NOAA Weather Radio doesn't sound its alert tone for Coastal Flood Advisories, only for Warnings.
What the alerts mean
NWS Key West explains its coastal flood alerts this way:
- Coastal Flood Statement: nuisance flooding is possible in low spots.
- Coastal Flood Advisory: some roads may become impassable, or driving through saltwater may be unavoidable.
- Coastal Flood Warning: saltwater is threatening property and affecting travel.
Where you live, the levels behind each alert may differ. Check your local NWS office. Our nor'easter and coastal flood guide explains the Coastal Flood Watch too.
Staying safe in tidal flooding
- Don't drive or walk through flooded roads. CDC says to avoid them, and the National Weather Service says never to drive around barriers.
- Be extra careful at night, when flooding is harder to see (NWS Melbourne).
- Secure loose objects outside before the high tide (NWS Melbourne).
- Don't stand on piers, jetties or sea walls to watch the water (NWS Melbourne).
- If you have to go into floodwater, wear rubber boots, and wash your hands with soap and clean water afterward. CDC says floodwater can carry trash and germs (CDC: Preparing for floods).
“A mere 6 inches of fast-moving flood water can knock over an adult. It takes just 12 inches of rushing water to carry away most cars and just 2 feet of rushing water can carry away SUVs and trucks.”National Weather Service, Turn Around Don't Drown
Protecting your home
Ready.gov suggests moving valuables to higher levels, clearing drains and gutters, and installing check valves (Ready.gov: Floods). Check your flood risk on FEMA's Flood Map Service Center, and remember flooding doesn't follow lines on a map.
Homeowners insurance usually doesn't cover flooding, and a new flood policy typically takes up to 30 days to start. See Flood insurance waiting period. If water got inside, photograph it first (photo checklist), then start drying within 24 to 48 hours (water damage and mold).
Common questions
What is a king tide?
NOAA says "king tide" is a non-scientific term for exceptionally high tides. They happen when the moon is new or full, and are higher still when the moon is closest to Earth or during certain seasons.
Why does my street flood when it isn't raining?
NOAA calls this high tide flooding, or sunny day flooding. Strong tides at the full or new moon, shifts in wind and ocean currents can push seawater onto low roads and into storm drains even on a clear day.
When are king tides highest in Florida?
NWS Key West says the highest tides in the Florida Keys usually come in the fall and early winter and peak around new and full moons.
Is it safe to drive through high tide flooding?
No. Ready.gov says not to walk, swim or drive through flood waters, and the National Weather Service says the road may have collapsed under the water. Turn around and find another route.
Does homeowners insurance cover high tide flooding?
Usually not. Ready.gov says homeowners policies do not cover flooding, and a new flood insurance policy typically takes up to 30 days to start.
Live coastal flood alerts for your area: pick your state on the States page, or see Flooding and Active weather events.