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Claim analyzed
Science“Storm tide is the sum of base sea level, astronomical tide, and storm surge.”
Submitted by Patient Hawk 07d5
The conclusion
Open in workbench →The claim is not supported by standard scientific definitions. Authoritative sources consistently define storm tide as the combination of storm surge and astronomical tide, not as a three-part sum. “Base sea level” is typically the datum or baseline used to measure water level, so adding it as a separate component misstates the term.
Caveats
- The claim conflates a measurement baseline with a physical contributor to water level.
- Primary authorities define storm tide as a two-component concept: astronomical tide plus storm surge.
- A three-term framing may describe absolute water level relative to a datum, but that is not the standard definition of storm tide.
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Sources
Sources used in the analysis
NOAA defines storm tide as: "Storm tide is the total observed seawater level during a storm, resulting from the combination of storm surge and the astronomical tide." It also defines storm surge as "the abnormal rise in seawater level during a storm, measured as the height of the water above the normal predicted astronomical tide." This description distinguishes storm tide (surge + astronomical tide) from the underlying predicted tide level or long‑term mean sea level.
This NOAA technical document states: "Storm surge is defined as the abnormal rise of water generated by a storm, over and above the normal astronomical tide, and is expressed in terms of height above predicted or expected tide levels." It then contrasts this with storm tide: "By contrast, storm tide is defined as the water level due to the combination of storm surge and the astronomical tide, and is expressed in terms of height above a vertical or tidal datum." It further notes that a vertical or tidal datum is a base elevation used as a reference from which to measure heights or depths.
The National Hurricane Center glossary explains: "Storm Surge: An abnormal rise of water generated by a storm, over and above the predicted astronomical tide." It then distinguishes: "Storm Tide: The water level rise during a storm due to the combination of storm surge and the astronomical tide." This makes clear that storm tide is defined as the sum of storm surge and the astronomical tide, relative to the usual tidal sea level reference.
NOAA’s MDL FAQ defines: "STORM SURGE is an abnormal rise of water generated by a storm, over and above the predicted astronomical tide." It then defines storm tide separately: "STORM TIDE is the water level rise during a storm due to the combination of storm surge and the astronomical tide." In this framing, storm tide is explicitly the sum of the storm surge component and the astronomical tide, both referenced to an appropriate datum.
In describing coastal water levels, NOAA explains that high tide flooding occurs when sea level rise combines with local factors: "High tide flooding occurs when sea level rise combines with local factors to push water levels above the normal high tide mark." Although not a definition of storm tide, this illustrates NOAA’s use of a baseline (normal high tide) plus additional components (e.g., sea level rise or surge) to describe total observed water level.
USGS, citing NOAA, defines storm tide as: "Storm tides is the combination of storm surge, which is water that has been pushed by a storm, with the regularly occurring tides." It further clarifies that storm surge is water pushed by a storm, and the storm tide is the actual sea level as influenced by the storm: "A storm tide is the actual sea level as influenced by a weather disturbance. The storm tide consists of the normal astronomical tide plus the storm surge (NOAA)."
The FAQ cites the National Hurricane Center: "According to the National Hurricane Center, storm surge is an abnormal rise of water generated by a storm, over and above the predicted astronomical tides. Storm tide is defined as the water level rise due to the combination of storm surge and the predicted astronomical tide." It also explains that a "base" sea surface elevation for mapping is determined using Highest Astronomical Tide and vertical datums, and then sea level rise and storm surge scenarios are added to this base level to get overall water level.
Woods Hole Oceanographic Institution distinguishes storm surge from storm tide: "Storm surge is an abnormal rise of water generated by a storm, over and above the predicted astronomical tides." It explicitly warns not to confuse the two: "Storm surge should not be confused with storm tide, which is defined as the water level rise due to the combination of storm surge and the astronomical tide." This reiterates that storm tide equals storm surge plus astronomical tide, both measured relative to a reference datum.
The UN disaster terminology entry states: "Storm tide is the total observed seawater level during a storm, which is the combination of storm surge (the rise in seawater level caused solely by a storm) and the astronomical tide (the change in water level due to the gravitational forces of the sun and moon)." This explicitly defines storm tide as the sum of storm surge and astronomical tide, representing the observed sea level during the storm.
On a slide titled “What is Storm Surge?” the presentation states: “STORM SURGE is an abnormal rise of water generated by a storm, over and above the predicted astronomical tide.” On the same slide it defines: “**STORM TIDE is the water level rise during a storm due to the combination of storm surge and the astronomical tide**.” A later slide gives a schematic: “Total water level = Storm surge + Tides + Wave setup + Freshwater.”
The UN terminology for storm surge explains: “Storm surge is an abnormal rise of water generated by a storm, over and above the normal astronomical tide.” It then clarifies storm tide: “A **storm tide is the water level that results from the combination of the storm surge and the normal (astronomical) tide**. A 3-metre (9.8 feet) storm surge on top of a 2-metre (6.6 feet) high tide produces a 5-metre (16.4 feet) storm tide.”
UNDRR’s hazard terminology entry states: "A storm tide is the actual sea level as influenced by a weather disturbance." It explicitly links to the NOAA formulation: "The storm tide consists of the normal astronomical tide plus the storm surge (NOAA)." This definition treats the storm tide as the sum of the astronomical tide and the storm‑induced surge, representing the observed sea level during the event.
In the section on fields for surge and tide, the Guide notes that “fields of the astronomical tide and surge provide a useful overview of the situation at sea,” and describes standard practice where “the **total water level at the coast** is obtained by **combining the predicted astronomical tide with the storm surge** produced by the forecasting system.” It follows the WMO/NOAA convention that storm tide is this combined water level during the storm.
In its section "Storm Surge vs. Storm Tide," the document notes: "Storm surge is defined as a change in sea level caused by a storm." It then says: "Storm tide is the total observed seawater level during a storm, resulting from the combination of storm surge and the astronomical tide." A later summary repeats: "Storm tide is a combination of an astronomical tide and a storm surge." This educational material directly describes storm tide as the combination (sum) of storm surge and astronomical tide.
ClimateCheck’s glossary states: "Storm Surge: The abnormal rise of water generated by a storm, over and above the normal astronomical tide." It defines: "Astronomical Tide: The tidal levels and water motion which result from the earth’s rotation and the gravitational effects of the earth, sun and moon." For storm tide it explains: "Storm Tide: The net effect of a storm surge and the astronomical tide. Not equivalent to the storm surge itself although the two are often confused." This indicates storm tide is the net (combined) water level from both surge and tide.
This engineering text explains that water level fluctuations at coasts include multiple components: "Water level fluctuations include astronomical tides, storm surges, and long-term sea level rise or fall." It defines storm surge as: "Storm surge is the rise of water level above the astronomical tide as a result of meteorological forcing." Although it does not explicitly define storm tide, this decomposition shows that total water level can be viewed as astronomical tide plus storm surge plus any long‑term sea level change relative to a datum such as mean sea level.
NOAA’s educational page notes how storm surge contributes to total water level: "Storm surge is water from the ocean that is pushed toward the shore by the force of the winds swirling around the hurricane." It then explains that this surge adds to the normal tide: "This advancing surge combines with the normal tides and can increase the water level by 30 feet or more." While it does not use the term "storm tide" here, the description matches the concept of total water level being the combination of surge and the astronomical tide.
The primer states: “Storm surge is the rise in seawater level caused solely by a storm.” It explains measurement: “Storm surge is the abnormal rise in seawater level during a storm, measured as the height of the water above the normal predicted astronomical tide.” It then defines storm tide: “**Storm tide is the total observed seawater level during a storm, resulting from the combination of storm surge and the astronomical tide.**”
The article explains: "A storm surge is an abnormal rise in seawater level during a storm, over and above the predicted astronomical tide." It then defines: "A storm tide is the combination of the storm surge and the normal astronomical tide. It represents the total observed sea level rise due to the combined effects of the surge and the tide." An example is given: "if a storm surge of 10 feet coincides with a high tide of 5 feet, the storm tide would reach 15 feet above the mean sea level."
The article defines storm surge as: "a coastal flood or tsunami-like phenomenon of rising water commonly associated with low pressure weather systems, such as tropical cyclones." In the terminology section it notes that storm tide refers to the combination of the storm surge and the astronomical tide, giving the total water level relative to a tidal datum such as mean sea level. This reflects the standard usage where storm tide is not an additional component but the resulting water level from surge plus tide.
This state hazard page explains: "Storm surge is the abnormal rise of water generated by a storm, over and above the predicted astronomical tide." It then clarifies: "Storm tide is the water level rise during a storm due to the combination of storm surge and the astronomical tide. It is the total observed seawater level during the storm." The description emphasizes that what communities experience as flooding is related to the full storm tide level, not storm surge alone.
In a section on coastal flooding, NOAA states that during storms, "storm surge is the water level rise above the predicted astronomical tide." It then explains that when this surge is added to the astronomical tide, "the resulting total water level is called the storm tide." The tutorial notes that the height of the storm tide relative to mean sea level determines the extent of coastal inundation.
In coastal oceanography and engineering, "base sea level" is typically represented by a vertical datum such as mean sea level (MSL) or a tidal datum (e.g., mean higher high water). These datums serve as the reference level from which both astronomical tides and storm surge heights are measured. Under this convention, the observed storm tide at any instant can be conceptualized as base sea level (datum) plus the tidal departure from the datum (astronomical tide) plus any meteorologically driven departure (storm surge).
In the explanatory caption and narration, the video states: “**The combination of storm surge and normal astronomical tide is known as a storm tide.**” The clip is used by a local disaster management office to educate residents about evacuation decisions based on expected storm tide levels.
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The arguments
Two AI advocates debated this claim using the research gathered.
Argument for
Authoritative scientific bodies explicitly define storm tide as the total observed seawater level resulting from the combination of storm surge and the astronomical tide (Source 1, Source 3, Source 8). When referenced to a vertical datum such as mean sea level, this total water level is mathematically and conceptually the sum of the base sea level, the astronomical tide, and the storm surge (Source 2, Source 23).
The Proponent commits a category error by conflating a reference datum with an additive component: Source 2 explicitly states that storm tide is expressed 'in terms of height above a vertical or tidal datum,' meaning the datum is the baseline from which measurements are taken, not a summand in the equation — a distinction the Proponent's argument obscures by selectively invoking Source 23, a low-authority background knowledge entry that contradicts the uniform two-component formulation found across all high-authority sources. Furthermore, every primary authoritative source cited — including Source 1, Source 3, Source 9, and Source 11 — defines storm tide exclusively as the sum of storm surge and astronomical tide, and none introduces 'base sea level' as a third discrete component, rendering the Proponent's mathematical reframing an unsupported logical inference rather than an established scientific definition.
Argument against
Every authoritative source in the research brief — including Source 1 (NOAA National Ocean Service), Source 3 (National Hurricane Center), Source 9 (PreventionWeb/UNDRR), and Source 11 (PreventionWeb) — consistently defines storm tide as the combination of storm surge and the astronomical tide only, with no mention of 'base sea level' as a separate additive component. The claim's inclusion of 'base sea level' as a distinct third summand misrepresents the standard definition, since as Source 2 (NOAA National Weather Service) clarifies, storm tide is expressed relative to a vertical or tidal datum — meaning any baseline is merely a reference point, not an added component in the sum.
The Opponent's argument relies on a semantic fallacy, failing to recognize that expressing a measurement relative to a vertical datum mathematically requires adding that base sea level reference to the tidal and surge departures (Source 2, Source 23). As Source 7 (Maine Geological Survey) and Source 16 (Pile Buck) demonstrate, calculating the actual, real-world water level of a storm tide inherently requires adding these storm and tidal components to a base sea level elevation.
Expert review
3 specialized AI experts evaluated the evidence and arguments.
Expert 1 — The Logic Examiner
The Proponent commits a category error by treating a reference datum (base sea level) as an additive physical component, whereas authoritative sources (Sources 1, 2, 3, and 11) define storm tide strictly as the two-component sum of storm surge and astronomical tide. The Opponent's rebuttal correctly identifies that a baseline datum is the starting point of measurement rather than a third physical summand, making the claim's three-part formulation logically and scientifically inaccurate.
Expert 2 — The Source Auditor
High-authority, independent definitional sources—NOAA NOS (Source 1), NOAA NWS technical note (Source 2), and NOAA NHC (Source 3), corroborated by USGS (Source 6) and UNDRR/PreventionWeb entries (Sources 9, 11, 12)—consistently define storm tide as the combination of storm surge and the astronomical tide, expressed relative to a vertical/tidal datum, without treating “base sea level” as an additional summed component. Therefore the claim's three-term definition (base sea level + astronomical tide + storm surge) is not the standard definition supported by the most reliable sources and is best judged false (at most, it's a reframing of absolute water level relative to a datum, not what “storm tide” is defined as).
Expert 3 — The Precision Analyst
The claim states that 'storm tide is the sum of base sea level, astronomical tide, and storm surge.' Every high-authority source in the evidence pool (Sources 1, 2, 3, 4, 6, 8, 9, 11, 12, 13, 14, 18, 19, 21, 22) consistently defines storm tide as the combination of exactly two components: storm surge and astronomical tide, expressed relative to a vertical or tidal datum. The datum (base sea level) is the reference point from which measurements are taken, not an additive component in the sum. The claim's inclusion of 'base sea level' as a distinct third summand misrepresents the standard scientific definition, which is a two-component formulation. While Source 23 (low-authority background knowledge) suggests a three-component conceptualization, this contradicts the uniform definition across all primary authoritative sources. The claim as worded is therefore false in its precision — it adds a third component ('base sea level') that authoritative sources treat as a reference datum, not an additive term.