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The problem of short-term sea level forecasting in the area of Сape Kamenny in the Ob’ Bay has become important since the Novoportovsky terminal (known as “Arctic Gate”) began operating for year-round oil shipment. The tankers loading the oil from the terminal have to pass through relatively shallow waters, located to the north, limiting the vessels draft. Thereby a short-term water level forecast is required relative to the lowest theoretical level for tankers loading at the terminal. The year-round hourly observations using buoy level gauges with a satellite channel of data transmission are organized for quick level monitoring directly in the area of Cape Kamenny. The results of the harmonic analysis of water level observations in the area of Cape Kamenny for 2016–2021 showed significant seasonal variability of amplitudes and phases of the wave М2 in the annual cycle, as well as their interannual variability due to various ice conditions of the Ob’ Bay (light, medium, heavy). Based on these results, the processing and analysis of observations data over the last month are performed by the end of each month. According to these results, the current values of harmonic constants, dependent on actual ice conditions are specified and calculation of the tide is carried out for the next month. The calculation of the forecast values of the total level is composed of calculated tide and short term (with a lead time of up to 5 days) forecast of non-periodic level fluctuations using the three-dimensional hydrodynamic model of joint water and ice circulation AARI-IOCM. At the final stage of the forecast preparation, the predicted level, usually calculated relative to the conditional long term average annual value, is bound to the lowest theoretical level (according to the current values of the level gauge) and transferred to the operator of the terminal and to the tanker. The hourly observations of water level in the area of Cape Kamenny and level forecasting have been carried out since 2017 and are still continuing.

Peculiarities of harmonic analysis of tides by using standard observation data of the sea level with a 6-hourly time step are considered. Masking frequencies causing difficulties when interpreting the results of the data analysis are presented. A method of control and editing of standard observations by using a non-recursive filter is proposed. The data interpolation approach based on direct and inverse Fourier transformation is considered.

Detailed data are presented on the seasonal time variations of the harmonic constants of the quarter-diurnal waves MN4, M4, MS4 and sixth-diurnal waves 2MN6, M6, 2MS6 obtained from the results of harmonic analysis of hourly tidal observations at Teriberka and Iokan’ga in the Barents Sea and Sosnovets, Kandalaksha, Kem-Port (Popov Island) and Arkhangelsk (Solombala Island) in the White Sea from 1977 to 1982 (1979). An extended least-squares technique is used. New compound waves are proposed for approximation of the seasonal variability of the harmonic constants of shallow-water waves and for a more complete description of the tide. An estimation of the prediction accuracy of tides with the addition of new compound shallow-water waves at Arkhangelsk and Kandalaksha has been performed.

Large-scale sea-level oscillations were investigated at 10 coastal stations in the Laptev Sea. Daily mean sea-level heights for the years 1962–1984 were used. Spectral analysis of time series reveals significant energetic peaks at 1 year, 28–30, 7–8, 5.2–5.3, 4.3, 3.0–3.3, 2.4–2.5 and 2.1–2.2 days. Long-period components were extracted using harmonic analysis on the basis of the least square method. The observed monthly tide exceeds the equilibrium tide by a factor of 1.45. Variance analysis of non-tidal (residual) time series shows that the maximum intensity of the sea-level oscillations is observed for periods of less than 1 year (from 66 to 81% of the total variance). From 13 to 24% of the total variance is accounted for by the long-period tides and 5–18% of the variance is due to interannual variability. An analysis of the two-dimensional distribution of temporal variations of amplitudes at the synoptic scale reveals their non-steady-state character for this range. Cross-spectral analysis of the non-tidal level oscillations indicates high coherence (0.68–0.98) between sea-level variations at the synoptic scale at different stations. The spatial distribution of phases shows that these sea level variations are mainly progressive waves in the range of less than 60 days. Calculated velocities of these waves are close to phase velocities of shelf waves and have a magnitude of 1.3–5.2 m/s for periods from 4 to 46 days.