About Swelldex and our data

Data sources and credit

• NOAA National Data Buoy Center (NDBC): wind speed, gusts and direction, wave height and period, and water temperature from buoys and coastal stations, via the public ndbc.noaa.gov real-time data files. Some stations are operated by partners (for example Scripps CDIP wave buoys and NOS water-level stations) and distributed by NDBC.
• NOAA CO-OPS Tides & Currents: high and low tide predictions from tidesandcurrents.noaa.gov (datum MLLW, local time).
• National Weather Service: point forecasts from the public api.weather.gov API. For boating decisions use the official NWS marine forecasts.

Thank you to NOAA and the NWS for making this data free and open. Swelldex is not affiliated with or endorsed by NOAA or the National Weather Service. We fetch the data through a small server function and cache it for about 15 minutes, so every page shows when each reading was observed.

How the ocean bite score works

Each port gets a daily 0–10 bite estimate for blue marlin and mahi-mahi offshore and redfish inshore. It is built from the latest NOAA buoy readings, NOAA tide predictions and the National Weather Service forecast for the next daylight period. It is an estimate of how good conditions look, not a prediction of catches. The score day is the next NWS daytime period (today while there's enough daylight left, otherwise tomorrow).

Offshore: blue marlin and mahi-mahi

• Sea state (0–5): The worse of wind and waves decides. Wind is the higher of the latest buoy reading and the NWS forecast for the day. Up to 10 kt and seas up to 2 ft score 5; 15 kt or 4 ft is still fishable for most boats; over 20 kt or 6 ft scores close to zero.
• Water temperature (0–5): Blue marlin score full marks at 74–84°F and mahi-mahi at 72–82°F, tapering off outside that range and reaching zero in cold water (below about 64°F for marlin, 62°F for mahi).
• Both have to line up: Offshore score = 10 × (sea points ÷ 5) × (temperature points ÷ 5). Perfect water in a gale scores low, and so does flat calm in cold water.
• Weather: Minus 1.5 if the NWS mentions a chance of thunderstorms, minus 3 if storms are likely (50%+), minus 4 for gales and minus 5 for tropical weather.

Inshore: redfish

• Water temperature (0–4): Redfish score 4 at 65–80°F, 3 a little outside that range, less in cold or very hot water.
• Wind (0–3): Up to 12 kt scores 3, up to 18 kt scores 2, up to 25 kt scores 1. Inshore water is more sheltered, so the scale is gentler than offshore.
• Tide movement (0–3): Bigger tidal range and more high/low changes in daylight mean more moving water, which tends to get fish feeding.
• Weather: The same thunderstorm, gale and tropical penalties as offshore.
• Range cap: Where redfish are seasonal or rare, the inshore score is capped and the page says why: Ocean City, MD at 6 and Montauk, NY at 3.

Labels: 8–10 Good · 6–7 Fair · 4–5 Slow · 0–3 Poor. If a reading is missing, that part is scored as neutral and the score is marked lower confidence.

What the score leaves out

Bait, current edges and weed lines, fishing pressure, moon phase, river runoff and local knowledge. Buoys can sit tens of miles from where you fish, and offshore water (for example the Gulf Stream or the canyons) can be much warmer or cooler than the nearest buoy. Treat the score as a first look, then read the conditions yourself.

Stations by port

Great Lakes bite score (a rougher estimate)

Great Lakes scores are rougher than the ocean scores and are capped at 9. Each Great Lakes spot gets a daily 0–9 bite estimate for its main species (walleye, yellow perch, king salmon, lake trout, steelhead or smallmouth bass). It combines wind and waves, surface water temperature against each species' preference, the time of year, the barometer trend and NWS storm wording. It is a rougher estimate than the ocean score: lake fish move with depth, structure and bait in ways surface data can't see.

• Wind and waves (0–5): The worse of the two decides. Wind is the higher of the latest station reading and the NWS forecast; waves are the higher of the latest buoy reading and the NWS gridded wave forecast for the day. Up to 8 kt and 1 ft scores 5; 15 kt or 3 ft is choppy (3); over 20 kt or 4 ft scores close to zero. Lake waves are short and steep, so the wave scale is stricter than offshore.
• Water temperature (0–5): Surface temperature against each species' preferred range: walleye 55–70°F, yellow perch 58–72°F, king salmon 44–58°F, lake trout 40–55°F, steelhead 40–58°F, smallmouth 60–75°F. Full marks inside, 3 in a wider acceptable band, less beyond. Salmon and trout hold deep in summer, so surface temperature is only a rough guide for them.
• Season (0–5): A month-by-month rating per species (for example walleye peak in spring and October, perch in August–September, kings in July–August, steelhead October–April, smallmouth June–September).
• Putting it together: Fish points = average of temperature and season points. Score = 10 × (wind/wave points ÷ 5) × (fish points ÷ 5), then the barometer and weather adjustments, capped at 9.
• Barometer: Using the 3-hour pressure tendency from the nearest station: falling slowly (1–3 hPa) +0.5; falling fast (3+ hPa) or rising fast (3+ hPa) −0.5; steady 0.
• Weather: Minus 1.5 if the NWS mentions a chance of thunderstorms, minus 3 if storms are likely (50%+), minus 4 for gales or storm warnings.
• Missing data: Many Great Lakes buoys are pulled for winter (roughly October to May). Readings then come from year-round shore stations, the NWS wave forecast and NOAA GLERL's daily satellite lake temperature (GLSEA). If an input is still missing it is scored as neutral and marked lower confidence.

Great Lakes data sources

• NOAA NDBC buoys and year-round shore stations (NOAA NOS water-level stations, GLERL and NWS stations, Coast Guard stations) for wind, waves, water temperature and pressure. Most lake buoys are seasonal and are pulled for winter; the page shows which ones are offline.
• NOAA CO-OPS Great Lakes water levels (feet above Low Water Datum, the chart datum) instead of tides.
• NOAA GLERL GLSEA (Great Lakes Surface Environmental Analysis): daily satellite lake-surface temperature, used when no station reports water temperature.
• National Weather Service: point forecast for each spot, the gridded wave-height forecast on the lake, and a link to the official nearshore marine forecast zone.

Species scored per spot: Chicago, IL: king salmon (chinook), yellow perch, smallmouth bass; Grand Haven, MI: king salmon (chinook), steelhead, yellow perch; Sturgeon Bay, WI: smallmouth bass, walleye, yellow perch; Duluth, MN: lake trout, walleye, steelhead; Saginaw Bay, MI: walleye, yellow perch, smallmouth bass; Port Huron, MI: walleye, yellow perch, steelhead; Port Clinton, OH: walleye, yellow perch, smallmouth bass; Erie, PA: walleye, yellow perch, steelhead; Oswego, NY: king salmon (chinook), steelhead, smallmouth bass. Fishing seasons, limits and closures (for example fall lake trout closures and bass catch-and-release seasons) vary by state and water: always check local regulations.

Corrections

Spotted a wrong station or a better buoy for a port? Contact form coming soon. Charter captains can reach us through Charters: get listed.