Hurricanes & Offshore Wind

July 10, 2025

Written by Sarah McElman, Lead Consultant at Metocean Expert Americas.

What are hurricanes, and how are they different from winter storms?

Unlike winter storms, which are created when a cold air mass and a warm air mass meet, creating a “front”, hurricanes form from “atmospheric waves” in the tropics and are sustained by heat from warm ocean temperatures. This means that trajectory, landfall location, and the “forward speed” of the hurricane all influence how the storm evolves in intensity and size. And because of the different temperature mechanisms at play, hurricanes occur at a different time of the year than winter storms. (The Atlantic Hurricane Season is June 1 – November 30.) This means that the Atlantic and Gulf coasts of the United States experience both hurricanes and winter storms, at varying frequencies and intensities, annually.

Tracking Hurricanes for Offshore Engineering

Typically smaller than winter storms, hurricanes and ocean features during a storm can be much more of a challenge to measure. With the advent of satellite-based observations, the global community’s models of these storms have improved, but features such as wave height, wave period, and its evolution within and outside of storm winds are still an active area of research. With luck, a well-placed and rugged buoy like those in NOAA’s National Data Buoy Center may capture ocean surface features, but whether the buoy is crossed near “the eye” or the far end of a storm—even on the left or right side of the storm—can register a big difference in measured values. Smart people from NOAA have been able to construct hurricane tracks back to 1850, which gives ocean engineers a collection of features to assess risk and is a starting point in determining extreme values for offshore design and operation. Given the relative size of today’s offshore wind projects in the United States, assessing hurricane-generated extreme values should therefore be repeated for multiple turbine locations across the project—and not just based on single metocean parameters that may appear to be the most conservative at one location or another.

Extreme Value Analysis (Briefly)

We determine extreme values for “return periods” such as 50-year or 100-year magnitudes based on the statistical methods of Extreme Value Analysis (EVA). When conducting EVA, a metocean analyst fits a parameter with a distribution from a set of storms (think “Weibull”) and then linearizes the distribution (the result is logarithmic). N-year values can then be determined from this linear model beyond the duration of the dataset.

Concerning the Atlantic Hurricane Season, consider that we only have 10-15 named storms a year, a fraction of which evolve into hurricanes and move close enough to the coast to measure in any given region. As a result, it can be a challenge to right-size an estimate of 100-year, 500-year, and 10,000-year extremes. (A 10,000-year return period is specified in European standards for properly sizing the offshore substation deck height. The American Petroleum Institute guidelines specify a 1,000-year value plus margin.)

Metocean Models for Offshore Wind

So how do we capture all of this when we design an offshore wind project? A typical metocean model is a hind cast (think hourly forecast, but into the past) of winds, waves, and currents. This is the basis of detailed design work, such as the Input to Design Basis Part A1 for foundations.

Normally, the metocean model length is set by the duration of global data that provide model boundary conditions. Typical metocean models for offshore wind in the North Sea region span about 30 years in length. Given the high variability of landfall, path, and strength of hurricanes captured on record, this time period does not give us a very large sample set to conduct EVA with reasonable uncertainty, even with a calibrated and validated model.

As a result, there are a few methods metocean analysts use to better represent extremes in regions with hurricane activity: synthetic modeling, which relies on historical tracks and Monte Carlo simulations (for more information, see IEC 61400-1 Annex J), and direct numerical modeling, such as Oceanweather’s 100+ years of recreated hurricanes. Both techniques have strengths and limitations, but they improve the quality and quantity of information available to metocean analysts to characterize the true extremes at a site.

Additional Modeling Needs

You can imagine that these small, complex storms are challenging to model for engineering purposes, and the work isn’t over. Researchers at the US’ National Laboratories and universities have projects underway–TREXO, STORM, and OWIND to name a few—to refine models and methods in order to better understand storm dynamics and continue informing offshore wind project design standards.

It’s thanks to forward-thinking collaborations between universities, governments, and industry players around the world that we’re writing the next stage of resilient energy infrastructure design.