Neaps

A tide prediction engine written in TypeScript.

Warning

Not for navigational use

Do not use calculations from this project for navigation, or depend on them in any situation where inaccuracies could result in harm to a person or property. Tide predictions are only as good as the harmonics data available, and these can be inconsistent and vary widely based on the accuracy of the source data and local conditions. The tide predictions do not factor events such as storm surge, wind waves, uplift, tsunamis, or sadly, climate change. 😢

Packages

This monorepo contains:

• neaps - Main tide prediction library with station finding
• @neaps/api - HTTP JSON API for tide predictions with OpenAPI specification
• @neaps/tide-predictor - Core harmonic tide prediction engine

Installation

npm install neaps

Usage

Tide Extremes Prediction

import { getExtremesPrediction } from "neaps";

const prediction = getExtremesPrediction({
  latitude: 26.7, // or `lat`
  longitude: -80.05, // or `lng` or `lon`
  start: new Date("2025-12-17"),
  end: new Date("2025-12-18"),
  datum: "MLLW", // optional, defaults to station's chart datum (usually LAT or MLLW)
  units: "meters", // optional, defaults to 'meters', can also be 'feet'
});

console.log(prediction);
// {
//   datum: 'MLLW',
//   units: 'meters',
//   station: {
//     id: '8723214',
//     name: 'Fort Lauderdale, FL',
//     // ...
//   },
//   distance: 12.3,
//   extremes: [
//     { time: 2019-01-01T03:12:00.000Z, level: 3.2, high: true, low: false, label: 'High' },
//     { time: 2019-01-01T09:45:00.000Z, level: 0.5, high: false, low: true, label: 'Low' },
//   ]
// }

Get Timeline Prediction

import { getTimelinePrediction } from "neaps";

const timeline = getTimelinePrediction({
  lat: 26.77,
  lon: -80.05,
  start: new Date("2025-12-19T00:00:00-05:00"),
  end: new Date("2025-12-19T01:00:00-05:00"),
  timeFidelity: 5 * 60, // seconds, defaults to `10 * 60`
  units: "meters", // optional, defaults to 'meters', can also be 'feet'
});

console.log(timeline);
// {
//   datum: 'MLLW',
//   units: 'meters',
//   station: {
//     id: 'noaa/8722588',
//     name: 'Port of Palm Beach',
//     // ...
//   },
//   timeline: [
//     { time: 2025-12-19T05:00:00.000Z, hour: 0, level: 0.7232836255650095 },
//     { time: 2025-12-19T05:06:00.000Z, hour: 0.1, level: 0.7231644154595303 },
//     { time: 2025-12-19T05:12:00.000Z, hour: 0.2, level: 0.7221097788490487 },
//     { time: 2025-12-19T05:18:00.000Z, hour: 0.3, level: 0.7201242512580206 },
//     // ...
//   ]
// }

Get Water Level at Specific Time

import { getWaterLevelAtTime } from "neaps";

const prediction = getWaterLevelAtTime({
  lat: 26.77,
  lon: -80.05,
  time: new Date("2025-12-19T00:30:00-05:00"),
  datum: "MSL",
  units: "meters", // optional, defaults to 'meters', can also be 'feet'
});

console.log(prediction);
// {
//   datum: 'MSL',
//   units: 'meters',
//   station: {
//     id: 'noaa/8722588',
//     name: 'Port of Palm Beach',
//     // ...
//   },
//   time: 2025-12-19T05:30:00.000Z,
//   hour: 0,
//   level: -0.43840585181640557
// }

Finding stations

Neaps uses @neaps/tide-database to find station data. You can find stations by location or ID.

Nearest Station

import { nearestStation } from "neaps";

const station = nearestStation({ lat: 26.7, lon: -80.05 });
console.log(`${station.name} (${station.source.id})`); // Fort Lauderdale, FL (8722588)

Once you've found a station, you can get predictions, timeline, or water level at a specific time for that station:

// Get extremes prediction for the nearest station
station.getExtremesPrediction({
  start: new Date("2025-12-17"),
  end: new Date("2025-12-18"),
});

// Get timeline prediction for the nearest station
station.getTimelinePrediction({
  start: new Date("2025-12-19"),
  end: new Date("2025-12-20"),
});

// Get timeline prediction for the nearest station
station.getWaterLevelAt({ time: new Date("2025-12-19T00:30:00-00:00") });

List Nearby Stations

import { stationsNear } from "neaps";

stationsNear({ latitude: 45.6, longitude: -122.7 }, 5).forEach((s) => {
  console.log(`${s.name} (${s.source.id}) - ${(s.distance / 1000).toFixed(2)} km away`);
});
// Vancouver (9440083) - 3.49 km away
// Portland Morrison Street Bridge (9439221) - 10.24 km away
// KNAPP(THORNES)LNDG, WILLOW BAR (9440171) - 16.34 km away
// Rocky Point (9439189) - 16.93 km away
// WASHOUGAL, COLUMBIA RIVER (9440047) - 24.89 km away

Find station by ID

import { findStation } from "neaps";

// Find station by Neaps ID
findStation("noaa/8443970"); // Boston

// Find station by source ID (e.g. NOAA)
findStation("9440083"); // Vancouver

Accuracy & Validation

Neaps is continuously validated against NOAA tidal predictions, comparing the time and height of predicted high and low tides for all NOAA tide stations.

Methodology

• High/low predictions over a full year extracted from both NOAA and Neaps for 3300+ NOAA reference and subordinate stations
• One-to-one event matching using a ±180-minute window
• Metrics computed per station and aggregated across all stations
• Evaluated automatically in CI on every change

Results

As of Feb 2026:

• Stations evaluated: 3,370
• High/low events compared: 4,522,258
• Median |Δt|: 0.6 minutes
• 95% of stations have median |Δt| < 4.3 minutes
• Median MAE: 5 mm
• 95% of stations have MAE < 17 mm

Summary

Neaps reproduces high and low tide timing with sub-minute accuracy and tide heights with millimeter-level accuracy compared to NOAA's tide predictions. Validation is automated and enforced in CI to prevent regressions as the model evolves.