About Ressacast
Ressacast is an experimental coastal-hazard forecast for Santos–Guarujá, São Sebastião and Ubatuba. It converts the combined effect of elevated sea level and wave energy into five qualitative classes: Low, Moderate, High, Very High and Extreme.
Input data
- Storm surge: water-surface-elevation forecasts from HYCOM ESPC-D-V02 Global Analysis. ESPC-D-V02 is a global coupled ocean and sea-ice prediction system generated with HYCOM and CICE and distributed on a global 1/12° grid. Ressacast retrieves the surf_el surface-elevation variable at representative coastal points and samples it every three hours. Although the source system provides a longer global forecast, the usable window available to the daily Ressacast acquisition normally results in approximately five to five and a half days of classification.
- Astronomical tide: minute-resolution harmonic tide predictions for Santos, São Sebastião and Ubatuba.
- Waves: local Wave Power in kW/m produced by GUAECAST. GUAECAST propagates offshore wave conditions from NOAA/NWS WaveWatch III through nested SWAN grids, with atmospheric forcing from GFS.
Calculation
- The total water level is calculated as astronomical tide + storm surge.
- The reference level is the maximum astronomical tide in the complete harmonic-tide series loaded by the system.
- The water-level excess is total water level − maximum astronomical tide.
- Wave Power and water-level excess are independently divided into five classes.
- The two classes are crossed in the risk matrix below. Wave energy alone does not activate a coastal alert: when total level does not exceed the astronomical reference, the Ressacast class remains Low.
- When storm-surge data end or any required value is invalid, the result is N/A; zero-filled values used elsewhere in the operational wave workflow are never classified by Ressacast.
Wave Power bins [kW/m]: <3 · ≥3 to <7 · ≥7 to <15 · ≥15 to <30 · ≥30
Water-level excess bins [m]: ≤0 · >0 to <0.10 · ≥0.10 to <0.20 · ≥0.20 to <0.40 · ≥0.40
Temporal resolution: 3 hours
Risk matrix
| Water-level excess | Wave Power (kW/m) | ||||
|---|---|---|---|---|---|
| <3 | 3–7 | 7–15 | 15–30 | ≥30 | |
| ≤ 0 m | Low | Low | Low | Low | Low |
| >0 to <0.10 m | Low | Low | Moderate | Moderate | High |
| ≥0.10 to <0.20 m | Low | Moderate | Moderate | High | Very High |
| ≥0.20 to <0.40 m | Moderate | Moderate | High | Very High | Extreme |
| ≥ 0.40 m | Moderate | High | Very High | Extreme | Extreme |
Meaning of the colors
- Low Normal coastal conditions.
- Moderate Increased coastal attention.
- High Hazardous coastal conditions.
- Very High Significant impacts are likely.
- Extreme Severe impacts are expected.
Limitations
Ressacast is a model-based regional indicator, not an observation or an official warning. Local impacts depend on beach orientation, morphology, coastal structures, model errors and the timing of wave and water-level peaks. The maps are generated automatically and should be interpreted with official meteorological and civil-defense information.