Marine Weather API for the Chesapeake Bay

Marine Weather Challenges on the Chesapeake Bay

The Chesapeake Bay stretches 200 miles from Havre de Grace, MD to Norfolk, VA — the largest estuary in the United States. Its mix of open water, narrow tributaries, and shallow depths creates weather conditions unlike anywhere else on the East Coast.

Annapolis is the sailing capital of the East Coast, with more boats per capita than anywhere in America. Yacht clubs, racing fleets, and cruisers all depend on accurate forecasts to plan their time on the water. A forecast for the main Bay channel won't match conditions in the Severn River or up the Eastern Shore.

The Bay's shallow average depth — just 21 feet — means wind waves build quickly but with very short periods of 2-4 seconds, making them steep and uncomfortable even at modest heights. A 3ft sea on the Bay feels far worse than a 3ft sea in open ocean.

Hampton Roads at the southern end is one of the world's largest naval bases, with commercial and military traffic that requires precise weather planning. And fishing — especially striped bass (rockfish), blue crab, and oysters — is both a major commercial industry and recreational pursuit across the entire Bay.

For developers building sailing, fishing, or waterfront applications, the Chesapeake demands forecasts that account for its unique shallow-water dynamics, fast-moving summer storms, and the wide variety of conditions across its 200-mile length.

Get a Marine Forecast for the Chesapeake Bay

Here's how to get an AI-powered marine weather forecast for Annapolis, MD — the sailing capital of the East Coast:

curl -X POST https://api.sealegs.ai/v3/spotcast \
  -H "X-API-Key: your_api_key" \
  -d '{
    "latitude": 38.9784,
    "longitude": -76.4922,
    "start_date": "2026-07-12",
    "num_days": 3,
    "vessel_info": {
      "type": "sailing",
      "length_ft": 35
    }
  }'

{
  "summary": "Good conditions for a 35ft sailing vessel off Annapolis.
    South-southwest winds 10-14kt, building to 16-18kt through the
    afternoon as the sea breeze develops. Seas 1-2ft at short
    3-second period in the main Bay channel — typical summer chop.
    Watch for afternoon thunderstorms after 3pm, with gusts
    potentially reaching 40kt. Morning conditions excellent for
    a run down to the Eastern Shore.",
  "daily_forecasts": [
    {
      "date": "2026-07-12",
      "classification": "Good",
      "confidence": 0.88,
      "wind_speed_kt": 12,
      "wind_gust_kt": 18,
      "wave_height_ft": 1.5,
      "wave_period_s": 3
    }
  ]
}

The same request works for any Chesapeake Bay coordinates. Use 39.2866, -76.6115 for Baltimore Inner Harbor, 38.7851, -76.2233 for St. Michaels on the Eastern Shore, or 37.0299, -76.2463 for Hampton Roads.

Key Weather Parameters for the Chesapeake Bay

The API returns a full set of marine weather parameters. For Chesapeake Bay waters, these are especially important:

• Wind speed & direction — Southerly flow in summer, northerly in winter; direction determines which shores have lee protection
• Wave height & period — Short period (2-4 seconds) is the defining characteristic of Bay waves; feels rougher than the same height at sea
• Gusts — Thunderstorm outflows and squall lines are the primary hazard; gust forecasts are essential for safe sailing
• Visibility — Fog advisories for river mouths, especially the Potomac, Patuxent, and the upper Bay
• Precipitation — Thunderstorm timing is critical for all Bay activities from racing to crabbing

Use Cases on the Chesapeake Bay

Popular Chesapeake Bay Coordinates

Here are commonly used coordinates for Chesapeake Bay marine forecasts:

• Annapolis, MD — 38.9784, -76.4922
• Baltimore Inner Harbor — 39.2866, -76.6115
• St. Michaels, MD (Eastern Shore) — 38.7851, -76.2233
• Solomons Island, MD — 38.3168, -76.4544
• Hampton Roads / Norfolk, VA — 37.0299, -76.2463
• Deltaville, VA — 37.5546, -76.3302
• Oxford, MD — 38.6865, -76.1722