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. Each daily cycle retrieves the most recent complete forecast available on the HYCOM server, normally from the previous day but, depending on server availability, potentially from two to four days earlier. The surface-elevation series at representative coastal points is filtered to isolate the non-tidal residual used as storm surge. The usable Ressacast horizon therefore follows the selected HYCOM run.
- Astronomical tide: local harmonic series for Santos, São Sebastião and Ubatuba, reconstructed from long measured sea-level records. These reconstructions use substantially more tidal constituents than the original tidal representation in HYCOM.
- 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 reconstructed as local astronomical tide + filtered HYCOM 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.