How We Calculate Tides

HighTideNearMe provides accurate tide predictions for 237 coastal locations across the United States. We believe in transparency about our data sources and methodology.

Data Source

Tide Prediction Methodology

NOAA generates tide predictions using harmonic analysis of historical water level data. This method analyzes patterns in past tide measurements to predict future tides with high accuracy.

Key Factors in Tide Predictions:

• Astronomical Forces: Gravitational pull of the moon and sun
• Local Geography: Coastline shape, water depth, and ocean floor topography
• Historical Patterns: Years of water level measurements at each station
• Harmonic Constants: Station-specific coefficients that account for local conditions

How HighTideNearMe Works

1. Data Collection

We fetch tide predictions daily from NOAA's API for all 237 active tide stations across the United States. This includes:

• All U.S. coastal states (Atlantic, Pacific, Gulf of Mexico, Great Lakes)
• Alaska, Hawaii, and U.S. territories
• 7-day forecasts for each station

2. Data Processing

We process the raw NOAA data to provide:

• Next High Tide: The upcoming high tide time and height
• Next Low Tide: The upcoming low tide time and height
• Significant High Tides: The highest tides of the year using local maxima with 30+ day spacing
• Significant Low Tides: The lowest tides of the year
• 7-Day Forecast: Complete tide schedule for the week ahead

3. Location Matching

Our geolocation system finds the nearest tide station to your location using the Haversine formula, which calculates great-circle distances between geographic coordinates.

Data Accuracy

NOAA tide predictions are highly accurate under normal weather conditions:

• Height Accuracy: Typically within ±6 inches (15 cm)
• Time Accuracy: Typically within ±15 minutes

Important Note: Actual water levels can differ from predictions due to:

• Weather conditions (atmospheric pressure, wind)
• Storms and storm surge
• Seasonal variations
• River runoff and rainfall

Update Frequency

Data Limitations

What tide predictions include:

• Astronomical tides (caused by moon and sun)
• Local geographic effects
• Seasonal patterns

What tide predictions DO NOT include:

• Weather effects (wind, pressure)
• Storm surge
• Tsunamis or seismic events
• Future sea level rise

Our Calculations

Significant Tides Algorithm

To find the "Significant High Tides" and "Significant Low Tides" of the year, we use a local maxima algorithm with temporal spacing:

1. Collect all high tides (or low tides) for the next 365 days
2. Sort by height (descending for highs, ascending for lows)
3. Select the highest/lowest tide as #1
4. Find the next highest/lowest tide that is at least 30 days away from all previously selected tides
5. Repeat until we have 3 significant tides

This ensures the "Significant Tides" represent distinct events throughout the year, not just consecutive days during a spring tide period.

Data Licensing

NOAA Data: All NOAA data is in the public domain as works of the U.S. Government (17 U.S.C. §105).

Our Presentation: The HighTideNearMe interface, design, and additional calculations are © 2026 HighTideNearMe. Our processed data and API are available under Creative Commons Attribution 4.0 (CC BY 4.0).

Privacy & Location Data

When you use our geolocation feature:

• Your location is processed entirely in your browser
• We do not store or transmit your coordinates to our servers
• We only calculate the nearest tide station locally
• No cookies or tracking beyond basic analytics

Contact & Questions

If you have questions about our data sources, methodology, or want to report an issue:

• Report Data Issues: Contact NOAA CO-OPS at tidesandcurrents.noaa.gov
• Website Issues: Reach out on X (Twitter) or LinkedIn

Related Resources

• Understanding NOAA Tide Predictions
• What Are King Tides?

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