Photo: Doc Searls · CC BY-SA 2.0More hazard damage per building is expected in Half Moon Bay than in 95% of U.S. towns, mostly from earthquakes
On FEMA’s National Risk Index, Half Moon Bay gets a D for hazard risk: higher expected damage per building than 95% of U.S. towns, #533 of 847 in California. Most of that expected damage is earthquakes (51%), then river and rain flooding (33%). Flood insurance has paid 6 claims here since 1978.
Graded on FEMA’s expected yearly building damage per dollar of building value (NRI v1.20, December 2025), weighted by where residents live; flood claims are shown, not graded. How hazard risk is graded
What Half Moon Bay faces
Each hazard’s share of the building damage FEMA expects here, and how its rate compares with the rest of the country.
Earthquakes
River and rain flooding
Tsunamis
Shares are of FEMA’s expected building damage, the measure the grade uses; ranks compare each hazard’s building-damage rate with all 85,154 U.S. census tracts. In FEMA’s terms, river and rain flooding is FEMA’s “Inland Flooding” (rivers and streams overflowing their banks, or rain overwhelming drainage). FEMA defines coastal flooding as high or rising tides and storm surge, so surge damage is counted there. Drought isn’t listed: FEMA counts its losses in crops only.
What’s behind Half Moon Bay’s grade
Earthquakes are 51% of the building damage FEMA expects in Half Moon Bay, and Half Moon Bay’s rate of earthquakes damage is in the top 4% of U.S. census tracts. Tsunamis add 12%, at a rate in the top 1% of U.S. census tracts.
D #533 of 847 in California; higher expected damage per building than 95% of U.S. towns (21,298).
Half Moon Bay’s residents live in 4 census tracts; FEMA’s figures are combined by where they live.
The typical California town has higher expected damage than 92% of U.S. towns; within the state, Half Moon Bay has more expected damage per building than 63% of California towns.
In dollars, FEMA expects about $15.5M a year in losses across Half Moon Bay: $13.2M to buildings, the rest to people and crops.
Does Half Moon Bay flood? Rarely: 6 flood claims since 1978
Every paid claim on a federal flood insurance policy in Half Moon Bay, from FEMA’s records: 1.3 per 1,000 homes, fewer than 71% of the 13,809 U.S. towns with a flood insurance record.
- The Winter storm1 claim · $5K
- The Pineapple Express - Southern1 claim · $13K
Half Moon Bay isn’t in FEMA’s Community Rating System, which cuts flood insurance up to 45% in towns that do extra flood-proofing.
Insurance rates: San Mateo County.4 federal disasters brought FEMA money to Half Moon Bay
Disasters that paid out in Half Moon Bay itself (aid to households or repair grants to the City of Half Moon Bay), newest first, with that year’s flood claims.
- 2023Severe Winter Storms, Straight-line Winds, Flooding, Landslides, and Mudslides$30K to the City of Half Moon Bay for repairs
- 2022Severe Winter Storms, Flooding, Landslides, and Mudslides75 households applied for aid$340K aid approved$499K to the City of Half Moon Bay for repairs
- 2006Severe Storms, Flooding, Landslides, and Mudslides$23K to the City of Half Moon Bay for repairs
- 2005Severe Storms, Flooding, Mudslides, and Landslides$10K to the City of Half Moon Bay for repairs
San Mateo County has had 19 natural disasters declared by the President since 1953, most often severe storms, then floods. Not counted: the 2005 Hurricane Katrina evacuee emergency, which covered counties that took in evacuees.
Also 2 FEMA wildfire suppression grants (Fire Management Assistance, not a disaster declaration) for fires in San Mateo County, 2010–2020.
Old photos of Half Moon Bay after a storm or flood belong in the town’s history. Add one, or share what you remember below.
Add to the Half Moon Bay archive →Half Moon Bay and its neighbors
Half Moon Bay is 2nd of the 2 graded towns here, from least expected damage per building to most. Tap a town to see its hazards.
| Town | Hazard risk | Mostly (buildings) | Flood claims |
|---|---|---|---|
| El Granada | Dmore damage than 92% | earthquakes | 1 |
| Half Moon Bay | Dmore damage than 95% | earthquakes | 6 |
Hazard risk = FEMA’s expected yearly building damage per dollar of building value, vs. the 21,298 U.S. towns we grade; the map is shaded by fifths of the same scale. Flood claims = paid federal flood insurance claims on record.
Get ready for what Half Moon Bay faces
A short kit for the hazards that drive the building damage here, what to check before you buy, and where neighbors get alerts.
- Drop, cover and hold on.
- Strap tall furniture and the water heater to the wall.
- Know how to shut off the gas.
- Turn around at flooded roads: a foot of moving water can carry off a car.
- Flood insurance usually takes 30 days to start, so buy it before the forecast.
- Keep papers and medicines up high, in a grab-and-go bag.
- Strong shaking or a sudden drop in the sea means head for high ground now.
- Learn the tsunami route signs near the shore.
- Stay away until officials say it’s safe.
- Look up the address on FEMA’s flood map.
- Ask the seller or landlord whether it has ever flooded, and what flood insurance costs there.
- Get a flood insurance quote early: policies usually start 30 days after you buy.
Know where neighbors sign up for alerts? Add it to the Handbook so everyone has it.
Questions about natural hazards in Half Moon Bay
Is Half Moon Bay at risk for natural disasters?
On FEMA’s National Risk Index, Half Moon Bay has higher expected damage per building than 95% of U.S. towns: D for hazard risk, #533 of 847 in California. Most of the expected damage is earthquakes (51%) and river and rain flooding (33%). This is FEMA’s model of an average year for today’s buildings, not a forecast.
Does Half Moon Bay flood?
Flood insurance has paid 6 claims in Half Moon Bay since 1978, $56K in all, or 1.3 per 1,000 homes, fewer than 71% of U.S. towns with a flood insurance record. The most claims came from Winter storm (1).
Is Half Moon Bay in a flood zone?
Flood zones are drawn street by street, so the answer depends on the address: look it up on FEMA’s flood map. In San Mateo County, 31% of homes in mapped flood zones carry federal flood insurance, and 1.8% of all homes do.
How much is flood insurance in Half Moon Bay?
FEMA’s Community Rating System list shows no discount for Half Moon Bay’s flood program. Premiums depend on the building; policies usually start 30 days after you buy, so get a quote early.
What was the biggest storm in Half Moon Bay?
By FEMA money that reached Half Moon Bay, Severe Winter Storms, Flooding, Landslides, and Mudslides (2022): 75 households applied for aid, $340K approved, and $499K to the City of Half Moon Bay for repairs. By flood claims, Winter storm: 1 paid, $5K.
Is Half Moon Bay at risk from earthquakes?
It is the largest share of the building damage FEMA expects here (51%), and Half Moon Bay’s rate for it is in the top 4% of U.S. census tracts.
Storm stories
Memories, warnings and help from neighbors in Half Moon Bay.
Sources: FEMA National Risk Index v1.20 (December 2025), census-tract table, combined by where Half Moon Bay’s residents lived in the 2020 census; OpenFEMA: NFIP redacted claims, multiple-loss properties, community status book and residential penetration rates, housing assistance (owners and renters), public assistance funded projects, hazard mitigation properties and disaster declarations. Homes: Census ACS 2020–24. Preparedness tips: Ready.gov. FEMA’s model is an average of expected damage, not a forecast. How hazard risk is graded.