Weather Codes Atlas
Decoding SYNOP, METAR/TAF, and the text forecasts you get over SSB.
METAR (aviation; useful on coast)
Example: KSFO 161756Z 28012KT 10SM FEW015 SCT200 18/12 A3002 RMK AO2
- KSFO — ICAO station (San Francisco).
- 161756Z — 16th day, 17:56 UTC.
- 28012KT — wind 280° at 12 kt.
- 10SM — visibility 10 statute miles.
- FEW015 SCT200 — few clouds at 1,500 ft, scattered at 20,000 ft.
- 18/12 — temp 18°C, dewpoint 12°C.
- A3002 — altimeter 30.02 inHg (≈ 1016 mb).
SYNOP (the coded marine/synoptic report)
WMO FM-12/13 format. Marine ships use FM-13 SHIP. Structure:
- Section 0 — identification (station/ship, date, time, position).
- Section 1 — meteorological core: wind, pressure, temp, dewpoint, weather, clouds.
- Section 2 — marine: sea state, waves, swell, SST, ice.
- Section 3 — climatological extras.
Example marine group: 22246 00812 20812 = wind/wave direction 224°, period 6 s, Hs 12 × 0.5 = 6 m, swell from 080°, period 12 s, Hs 6 m.
Offshore/High-seas text forecast (NOAA format)
Sent over SSB/NAVTEX/Saildocs. Structure is always:
- Synopsis — current pattern: lows, highs, fronts with lat/lon.
- Forecast by period — TODAY, TONIGHT, FRI, FRI NIGHT, SAT.
- For each: wind (direction and kt range), seas (ft, period), weather (scattered showers, etc.).
Example: NE WINDS 20 TO 30 KT. SEAS 10 TO 15 FT. SCATTERED SHOWERS.
Marine warning tiers
| Category | Sustained wind |
|---|---|
| Small Craft Advisory | 22–33 kt (varies by region) |
| Gale Warning | 34–47 kt |
| Storm Warning | 48–63 kt |
| Hurricane Force Warning | ≥ 64 kt (non-tropical) |
| Tropical Storm Warning | 34–63 kt, tropical system |
| Hurricane Warning | ≥ 64 kt, tropical system |