Spending time on the Merrimack River in Newburyport, Massachusetts, you quickly understand why its mouth is considered one of the most dangerous river entrances on the New England coast. On days that appear modest offshore, the bar can produce steep, breaking waves that rise with little warning. The conditions are notoriously unpredictable, and that unpredictability has real consequences.

U.S. Coast Guard Station Merrimack River is one of only 19 designated surf stations in the country. This designation is reserved for locations that experience breaking surf greater than eight feet more than 36 days each year. The Merrimack earns that designation consistently.

What makes this river mouth so difficult is that its conditions are not driven by offshore forecasts alone. They are the result of interacting forces. Wind speed and direction, tidal phase, river discharge, and the geometry of the inlet all combine to shape what happens at the bar. The underlying physics are well understood. Wave-current interaction, shoaling, and tidal hydraulics have been studied for decades. The gap is in application. No existing tool assembles these factors into a system that models the reality of this specific location. A mariner can review standard forecasts on a relatively calm day and still encounter standing, breaking waves in the channel.

My name is Caleb Barlow. I am an engineer and an avid fisherman on the Merrimack. Like many who navigate this river, I have learned its lessons through experience, and sometimes through close calls. I have buried the bow of my boat beneath breaking surf multiple times. I have learned the L approach along the North Jetty. I have also arrived at the mouth with a boat full of kids on what appeared to be a calm day, only to turn around after seeing conditions that no forecast had prepared me for. I have spent years thinking about this problem. Why is there no tool that reflects what actually happens here?

The challenge was not a lack of theory. The challenge was applying it in a way that captures the complexity of this specific river. Translating physical principles into a working model of the Merrimack is not something that can be done by hand. It requires combining multiple interacting systems and tuning them to local conditions. That became possible with the use of modern artificial intelligence.

This application is not another weather app. It does not simply report offshore wave height or wind speed. It is a working model of the river itself. Built with AI, it integrates the physics of wave formation, current interaction, and tidal behavior with the actual geometry of the inlet. The system evaluates wave height, steepness, and period alongside tidal state and river flow to determine how waves will form and behave at the mouth.

The model was calibrated over several months using real-world feedback. Predictions were compared against camera footage of the river entrance and detailed accounts from experienced captains. I also conducted a high-resolution side-scan sonar survey of the bar at approximately one foot resolution. This provided bathymetric detail far beyond what is available in public charts and allowed the model to reflect the true shape of the riverbed.

The application now spans more than 5,000 lines of code and continues to improve as new data is incorporated. Nearly every year this river claims lives. The goal is to give mariners one more tool, using artificial intelligence, to make better-informed decisions before crossing.

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 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.