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Preliminary observed water levels account for vertical land motion (VLM) at a rate of 2.76 mm/yr, while tidal predictions account for regional sea-level (ReSL) change at 1.99 mm/yr (Patton et al., 2023; NHE, 2026).
The plot and summary table below update every 15 minutes, although the underlying data may not. Check the data
access date and time to confirm when the data were last retrieved. Allow a few seconds for the plot to load.
Disclaimer: Preliminary NOAA data have not undergone quality assurance or quality control (QA/QC) and may
not meet NOAA’s standards for official data. NOAA may revise these data; use with appropriate caution.
Detailed Notes: Adjusted Tide Station (2-day Residual) Plot [More]
Adjusted Tide Station (2-day Residual) Plot
About the Plot:
The interactive plot displays yesterday's and today's water levels at the station, including the adjusted predicted tide (blue), adjusted preliminary observed water levels (red), and tidal residuals (green). A dotted vertical line identifies when NOAA data were last retrieved. To the right of this line, the plot displays predicted tides for the remainder of today.
Use the English (ft) and Metric (m) buttons to switch units, hover over the plot to view individual values, and use the camera button to save the plot and summary table as an image.
Water Levels and Adjustments:
All water levels are referenced to the North American Vertical Datum of 1988 (NAVD88). We adjust observed water levels for vertical land motion (VLM), which represents the gradual rise or sinking of land at the tide station. We adjust NOAA's tidal predictions for regional sea-level (ReSL) change, using a rate of 1.99 mm/yr.
Both adjustments use 1992.5 as the reference year, corresponding to the midpoint of the 1983–2001 National Tidal Datum Epoch. Together, these adjustments account for long-term relative sea-level change and provide a consistent reference for comparing observed and predicted water levels. The resulting tidal residuals primarily reflect non-tidal water-level variability rather than the long-term sea-level trend.
A negative VLM rate indicates land subsidence, while a positive rate indicates land uplift (Patton et al., 2023; NHE, 2026).
Tidal Residual (Green Line):
The tidal residual is the difference between adjusted observed and adjusted predicted water levels. Positive residuals indicate water levels above the predicted tide, while negative residuals indicate water levels below the predicted tide.
Tidal residuals reflect non-tidal influences, including winds, atmospheric pressure, river flow, and oceanographic conditions associated with seasonal variability and El Niño.
Skew Surge:
Skew surge is the difference between the highest observed water level during a tidal cycle and the corresponding predicted high water level, even when the two peaks occur at different times.
Unlike the largest instantaneous tidal residual, which may occur near low tide, skew surge measures how much higher or lower the observed high water level was than predicted. This makes skew surge particularly relevant to coastal flooding, which often occurs near high tide.
Summary Table:
The summary table reports the following values for yesterday and today, based on local Pacific calendar days:
Max Preliminary: Highest adjusted observed water level for the day.
Max Predicted: Highest adjusted predicted water level for the day.
Mean Tidal Residual: Average tidal residual over the available observations for the day.
Max Skew Surge: Largest skew surge among the day's completed high tides.
For today's ongoing tide, the table includes only completed high tides when calculating maximum skew surge. A tidal cycle is considered complete at the following predicted low tide. The table displays "pending" until the first high tide is complete and marks today's preliminary maximum skew surge with an asterisk (*) until all high tides for the day are complete.
Today's observed values and mean tidal residual reflect only the data available at the time of the latest update.
Time Axis:
The plots use local Pacific time (PST or PDT). When the two-day display spans a daylight saving time transition in March or November, the entire plot uses Pacific Standard Time (PST) to maintain a continuous time axis through the skipped or repeated hour. The time-axis label identifies this adjustment.
Updates:
An automated R script retrieves the latest NOAA data and updates the plots and summary tables every 15 minutes. NOAA's preliminary observations generally become available within minutes but may be delayed. Check the NOAA data access time displayed in the plot title to determine when the observations were last retrieved.
Preliminary Data:
Preliminary NOAA data have not undergone quality assurance or quality control (QA/QC) and may not meet NOAA's standards for official data. NOAA may revise these data; use with appropriate caution.
Related Pages:
The Sea-Level Anomaly pages display monthly sea-level anomalies and compare the current season with historical conditions and past El Niño events.
The Sea-Level Synthesis pages combine monthly anomalies, daily mean tidal residuals, and daily maximum skew surge over each station's historical record to illustrate sustained and short-term non-tidal water-level variability.
Data Sources:
NOAA Center for Operational Oceanographic Products and Services (CO-OPS): Preliminary 6-minute observed water levels and astronomical tidal predictions.
Vertical land motion and regional sea-level change: Patton et al. (2023); NHE (2026).
Crescent City (9419750):
Relative sea-level trend: −0.76 mm/yr, indicating a slight decline in relative sea level because land uplift exceeds regional sea-level rise.
Vertical land motion: 2.76 mm/yr (land uplift).
Developed by: Jeff Anderson (NHE)
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