The National Weather Service office in Ruskin writes the marine forecast for Tampa Bay and the Gulf from Bonita Beach to the Suwannee River, out to 60 nautical miles. It's free, it's updated at least four times a day, and it's the single most useful thing you can read before you hitch up the boat. Here's how to get the most out of it.
Pick the right zone
The forecast is split into zones, each with a code. For Tampa Bay you need up to three of them:
- GMZ830, Tampa Bay waters. Everything inside the bay.
- GMZ853, coastal waters from Englewood to Tarpon Springs out 20 nautical miles. The beaches, the passes and the nearshore reefs.
- GMZ873, waters from Englewood to Tarpon Springs from 20 to 60 nautical miles. Offshore.
Past 60 nautical miles, including the run to the Middle Grounds, the Ruskin office's zones end. Out there, read the National Hurricane Center's Offshore Waters Forecast for zone GMZ057.
There's also a synopsis (GMZ800) at the top that describes the big picture: fronts, high pressure, tropical systems. Read it first. It tells you why the wind is doing what it's doing and how long that will last.
If you're running past 20 miles, read both the coastal and the offshore zone, because you'll cross both and the offshore forecast is often rougher. The zone list links each forecast, and the full text has every zone on one page.
Keep in mind that the 20- and 60-mile lines are forecast boundaries, not fishing ones. State waters end 9 nautical miles out, and that's the line that decides which fishing rules apply.
What the numbers mean
Seas. Wave heights are forecast as significant wave height: the average of the highest third of the waves. Plenty of waves will be smaller, but the forecast itself warns that the highest waves may now and then be twice that size. With seas of 3 to 4 feet, a rare 6- to 8-footer is possible.
"Occasionally to." Many forecasts add a bigger number, such as "Seas 5 to 7 feet, occasionally to 9 feet." Plan for the bigger number.
Wave detail. The coastal and offshore zones often break the seas into separate wave trains, for example "Southwest 7 feet at 10 seconds and south 4 feet at 6 seconds." The second number in each pair is the period, the time between waves. Short-period waves, 5 or 6 seconds, are steep and close together and feel far worse than their height suggests. Longer-period swells are easier on a small boat.
Chop. Inside the bay the forecast mostly describes the surface rather than giving seas: smooth, light chop, a moderate chop, choppy or rough. When the wind is up it may add a wave height as well, as in "Waves 2 to 3 feet. Bay and inland waters choppy." The coastal zones add the same "bay and inland waters" line. Smooth and light chop are easy days. By choppy, a small boat is in for a wet, bumpy ride.
Thunderstorms. Each zone ends with a reminder that winds and waves are higher in and near thunderstorms. Afternoon storms are common in summer, so plan to be in, or close to the ramp, before they build.
Advisories and cautions
Headlines in capitals at the top of a zone are the ones that matter most.
- Small Craft Advisory. In the Weather Service's Southern Region, which includes Florida, an advisory goes out for average winds of 20 knots or more, or seas of 7 feet or more, lasting two hours or longer. It isn't a law, but it's written for exactly the kind of boat most of us trailer to the ramp.
- Small craft should exercise caution. Used for the first forecast period when conditions are just below advisory level: winds of 15 to 20 knots, or 6-foot seas.
Both can apply to the bay as well as the Gulf. A Small Craft Advisory for Tampa Bay waters with 20-knot winds can mean a rough, wet ride even though the waves are only 2 or 3 feet.
Check the buoys
A forecast is a prediction. The buoys tell you what's actually happening. The ones that matter around Tampa Bay:
- 42098, Egmont Channel Entrance, at the outer end of the shipping channel about 9 nautical miles west of Egmont Key. Waves and water temperature, but no wind.
- 42013, on the 25-meter (about 82-foot) depth line to the south. Wind, pressure and water temperature; wave readings are often missing.
- 42022, farther out on the 50-meter line.
- 42099, Offshore St. Petersburg, a wave buoy well offshore.
- 42036, West Tampa, about 112 nautical miles west-northwest of Tampa. Useful for seeing what's coming across the Gulf.
Compare them with the forecast. If the buoys already show more wind or bigger seas than forecast, believe the buoys.
Our Tampa Bay page puts the latest forecast for all three zones next to the buoy readings and tides, so you can check everything in one place.
A simple go or no-go routine
- The night before: read the synopsis and your zones. Note any advisory and when the wind is expected to change.
- In the morning: check the time the latest forecast was issued. If there's a newer one since last night, read it again.
- At the ramp: check the buoys and look at the water. If what you see doesn't match the forecast, go with what you see.
- On the water: keep watching the sky. Plan your run home with a margin for weather that comes in earlier than forecast.
In the bay itself, remember that the main ship channel is deep water with big traffic. Stay clear when a large vessel is coming.
Before you go
Check the conditions on our Tampa Bay page, tell someone where you're going and when you'll be back, and keep a radio on board. If you're heading to the reefs, our guide to Tampa Bay's artificial reefs covers how far out each one is.