Marine Weather API for Hawaii

Marine Weather Challenges in Hawaii

Hawaii sits in the middle of the North Pacific, exposed to swell from storms thousands of miles away. The islands intercept energy from every direction — massive northwest swells in winter, long-period south swells in summer, and constant trade wind chop from the east. No two coastlines see the same conditions on any given day.

Trade winds are the defining feature — consistent northeast winds of 15-25kt that make windward shores rough and leeward shores calm. When the trades drop or Kona winds blow from the south, the entire pattern reverses and normally protected coastlines become exposed.

The inter-island channels are notorious for amplified conditions — winds accelerate and seas steepen as they're funneled between islands. The Alenuihaha Channel between Maui and Big Island is one of the roughest stretches of water in the Hawaiian Islands.

Understanding the swell window (direction, height, period) is critical for anyone operating in Hawaiian waters. A 15ft northwest swell will hammer the north shore while the south shore stays flat, and vice versa for summer south swells.

Get a Marine Forecast for Hawaii

Here's how to get an AI-powered marine weather forecast for Honolulu / Waikiki — one of the busiest marine areas in the Hawaiian Islands:

curl -X POST https://api.sealegs.ai/v3/spotcast \
  -H "X-API-Key: your_api_key" \
  -d '{
    "latitude": 21.2869,
    "longitude": -157.8170,
    "start_date": "2026-01-20",
    "num_days": 3,
    "vessel_info": {
      "type": "sailing",
      "length_ft": 44
    }
  }'

{
  "summary": "Mixed conditions for a 44ft sailing vessel off Honolulu.
    Northeast trade winds 18-22kt, typical for winter. The south
    shore sees 2-3ft seas at a comfortable 12-second period from
    distant southern hemisphere swell. North shore has 8-12ft surf
    from a northwest swell — avoid north-facing harbors and
    anchorages. Kaiwi Channel crossing to Molokai would be rough —
    6-8ft seas with steep wind waves stacking on the swell. Good
    conditions for leeward coast sailing from Waikiki to Ko Olina.",
  "daily_forecasts": [
    {
      "date": "2026-01-20",
      "classification": "Good",
      "confidence": 0.88,
      "wind_speed_kt": 20,
      "wind_gust_kt": 26,
      "wave_height_ft": 3.1,
      "wave_period_s": 12
    }
  ]
}

The same request works for any Hawaii coordinates. Use 20.8783, -156.6825 for Lahaina, Maui, 19.6400, -155.9969 for Kailua-Kona, or 22.2092, -159.5036 for Hanalei Bay, Kauai.

Key Weather Parameters for Hawaii

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

• Swell height, direction & period — THE most important parameter for Hawaii; determines surf conditions and channel safety
• Wind speed & direction — Trade wind strength dictates daily operations; Kona wind days change everything
• Wave height & period — Distinguish between trade wind chop (short period) and long-period ocean swell
• Wind gusts — Channel crossings see amplified gusts as wind funnels between islands
• AI classification — The daily GO / CAUTION / NO-GO rating accounts for how all parameters interact for your vessel type

Use Cases in Hawaii

Popular Hawaii Coordinates

Here are commonly used coordinates for Hawaii marine forecasts:

• Honolulu / Waikiki — 21.2869, -157.8170
• Lahaina, Maui — 20.8783, -156.6825
• Kailua-Kona, Big Island — 19.6400, -155.9969
• Hanalei Bay, Kauai — 22.2092, -159.5036
• Kaiwi Channel (Molokai) — 21.2500, -157.3000
• Maui / Molokini Crater — 20.6318, -156.4965