The Merrimack River mouth at Newburyport, Massachusetts is one of the most dangerous inlet crossings on the New England coast — and one of the most poorly served by existing weather and marine forecast tools.

US Coast Guard Station Merrimack River is one of only 19 surf stations in the United States, a designation reserved for stations that regularly operate in seas greater than 8 feet or winds exceeding 30 knots. It is the only surf station in New England and one of just four along the entire East Coast. That designation exists because this entrance earns it, year after year.

The crossing is notoriously unpredictable. Large, dangerous waves can form at the bar in conditions that appear modest offshore. The reason is that what happens at the Merrimack mouth is not primarily a function of what is happening at sea — it is a function of the interaction between wind, wind direction, tidal phase, river discharge, and the unique bathymetry of the entrance. Those variables combine in ways that standard marine forecasts do not capture. NOAA buoy data and National Weather Service coastal forecasts describe offshore conditions. None of them describe what happens when those conditions meet the shallow bar, the narrow channel, the opposing ebb current and freshwater river outflow, and the particular vulnerability of this inlet to waves arriving from the east-northeast.

A mariner consulting standard sources on a day with modest offshore wave heights and a moderate easterly wind may have no indication that the bar is already producing steep, near-standing breaking waves. This application was built specifically to fill that gap. Nearly every year this river claims lives. The goal here is to give mariners one more tool — an imperfect one, but a specific one — to make a better-informed decision before crossing.

My name is Caleb Barlow. I am an engineer who has spent most of my career in the cybersecurity and intelligence fields. I am also a regular fisherman and mariner on the Merrimack River who has spent years thinking about this problem.

The physics of what happens at a river mouth bar are well understood. Shoaling, wave-current interaction, fetch-limited wave generation, tidal hydraulics — these are established principles of coastal oceanography. The problem was never the physics. The problem was that assembling those principles into a model tuned to this specific entrance — with its specific geometry, bathymetry, current patterns, and hazard conditions — was simply too complicated to do by hand. The formulas existed. Applying them correctly to the Merrimack, with all its local complexity, was the hard part.

This application represents an extensive collaboration between human expertise and artificial intelligence. AI was used to research and validate the physical formulas appropriate for this environment, identify and verify data sources, work through the geometry of the coastline and inlet orientation, identify and correct errors in the underlying calculations, and continuously refine the output based on known physical behavior. The result is a model that accounts for multiple interacting factors simultaneously — not just wave height in isolation, but the combination of wave character, steepness, period, tidal state, and river flow that together determine whether conditions are manageable or dangerous for a vessel of typical recreational size crossing the bar.

A mathematical model built by AI, however, still needs to be tuned by someone who knows the water. That human-in-the-loop feedback was the most important part of the development process. The model was calibrated by cross-referencing estimated wave heights against camera footage of the mouth, historical fishing reports, and mariner accounts — including podcasts where captains described in detail how waves form and behave in different conditions, and what navigation techniques work in each. The bathymetry underlying the model was informed by a side-scan sonar survey of the mouth conducted using a Garmin QuickDraw system at approximately one-foot resolution — a level of detail that no publicly available chart provides. The result is a substantial AI model of the river mouth now spanning nearly 5,000 lines of code.

The model knows this river because the people who built it fish it.

This application is provided for informational purposes only. It was developed with extensive AI assistance, and AI systems are known to produce errors — including confident-sounding errors that may appear credible but are incorrect, a phenomenon known as hallucination. The model has not been independently validated or peer reviewed. Conditions at the Merrimack bar can change faster than any model updates.

By using this application you acknowledge that crossing the Merrimack River bar involves inherent and serious risk, that this application may contain errors, and that you assume full and sole responsibility for all navigation and crossing decisions. Caleb Barlow and any associated parties accept no liability whatsoever for injury, death, vessel damage, or any other loss arising from decisions made in reliance on its output. This application is provided as-is without warranty of any kind. Use at your own risk.

No application replaces direct visual observation of the bar, local knowledge, and the judgment of an experienced mariner.

IMPORTANT SAFETY NOTICE — PLEASE READ BEFORE USE

Merrimack Wave Calculator is an informational tool that estimates wave height and bar crossing conditions at the mouth of the Merrimack River in Newburyport, Massachusetts. It is provided for general informational purposes only and must not be used as the sole basis for any navigation or crossing decision.

AI-Assisted Development
This application was developed with the extensive assistance of artificial intelligence. While the underlying physical model is based on established coastal engineering principles, AI systems — including those used in the development of this application — are known to produce errors, omissions, and confident-sounding but incorrect outputs, a phenomenon commonly referred to as "hallucination." The wave height model, its calibration constants, and its methodology have not been independently certified, peer reviewed, or validated against measured Merrimack bar conditions. Users should treat all outputs as estimates subject to significant uncertainty.

Assumption of Risk & Limitation of Liability
The Merrimack River bar is one of the most dangerous inlet crossings on the New England coast. People have died attempting to cross it in conditions that appeared manageable. No application, forecast, or instrument replaces direct visual observation of bar conditions, local knowledge, and the judgment of an experienced mariner. By using this application you acknowledge that you have read and understood this disclaimer, that crossing the Merrimack River bar involves inherent and serious risk, that this application may contain errors, and that you assume full and sole responsibility for all navigation and crossing decisions. The author and operator of this application, Caleb Barlow, and any associated parties accept no liability whatsoever for injury, death, vessel damage, or any other loss arising from decisions made in reliance on its output.

This application is provided "as is" without warranty of any kind, express or implied. Use at your own risk.

© 2026 Caleb Barlow. All rights reserved. Proprietary wave height methodology.