Arena Cove (9416841) Tide Station

Historical Anomaly and MEI Plot (First Plot)

Monthly mean sea level after removing the long-term relative sea-level trend (1.18 mm/yr) and average seasonal cycle. Zero (0) represents the expected sea level for each month after accounting for the long-term trend and typical seasonal cycle. Positive anomalies indicate higher-than-normal sea levels.

Top panel: All available station data

Shows monthly mean sea-level anomaly for station's historic record:

• Light line: Monthly sea-level anomalies.

• Bold line: Centered 13-month running mean, calculated when at least 10 of the 13 months have data. Because the running mean is centered, it ends approximately 6 months before the latest month.

• Red: Months since January of the year in which the current July–June season began.

• Filled circles: NOAA verified monthly means.

• Open circles: Preliminary monthly values calculated from NOAA 6-minute data, including the current month to date. These data have not undergone quality assurance or quality control (QA/QC).

Bottom panel: MEI index

The Multivariate ENSO Index (MEI) indicates El Niño and La Niña conditions. Orange bars show positive MEI values (El Niño side), while blue bars show negative values (La Niña side). The dashed line marks MEI = 1.0.

Grey bands: 

El Niño periods identified by MEI ≥ 1.0 for at least five consecutive months.

Using the plot: 

Use the 10 yr, 20 yr, 30 yr, or All buttons, or the slider below the plot, to select a time period. Hover over the plot to view monthly anomalies, the running mean, and MEI values in the hover information. Water-level values appear in both feet and meters. Use the English (ft) and Metric (m) buttons to switch display units.

Data sources:

• NOAA CO-OPS: Verified monthly means and 6-minute water levels used to calculate preliminary monthly values.

• NOAA Physical Sciences Laboratory (PSL): MEI.v2 (1979 onward), extended before 1979 using MEI.ext.

• Relative sea-level (RSL) change rates: NHE (2026).

Seasonal Anomaly Plot (Second Plot)

Monthly mean sea level after removing the long-term relative sea-level trend (1.18 mm/yr) and average seasonal cycle. Zero (0) represents the expected sea level for each month. Seasons run from July through June, keeping the fall and winter months of an El Niño event within the same season.

Top panel: Comparison with all years

Grey box plots show the distribution of monthly anomalies across all previous seasons, including El Niño years. Each box represents the middle 50% of values, the line marks the median, and points show individual years.

• Red: Current season, with each month's rank and total number of years used in the comparison (1 = highest anomaly on record for that month).

• Light red: Previous season.

Bottom panel: Comparison with past El Niño seasons

Shows historical El Niño seasons (MEI ≥ 1.0 for at least five consecutive months) within the station's record. Colors highlight the three largest recent events, while grey lines show the remaining El Niño seasons.

• Dashed line: Average of the historical El Niño seasons.

• Red: Current season.

Preliminary data (open circles): 

Open circles identify preliminary monthly values calculated from NOAA 6-minute data, including the current month to date. These data have not undergone quality assurance or quality control (QA/QC).

Using the plot: 

Hover over a point to view its value in feet and meters, the season, and the current season's rank where applicable. Use the English (ft) and Metric (m) buttons to switch units. Click a legend entry to hide or show the corresponding data.

Data sources:

• NOAA CO-OPS: Verified monthly means and 6-minute water levels used to calculate preliminary monthly values.

• NOAA Physical Sciences Laboratory (PSL): MEI data used to identify historical El Niño seasons.

• Relative sea-level (RSL) change rates: NHE (2026).

Developed by: Jeff Anderson (NHE)