Guide
Small craft advisories and Mississippi Sound
Checked September 29, 2026 against the National Weather Service office in New Orleans/Baton Rouge and the National Weather Service’s marine definitions.
The Marine tile repeats the National Weather Service’s coastal waters forecast for the water your town opens onto. On this coast that is Mississippi Sound, the shallow water between the beaches and the barrier islands, and every town on the board reads the same zone. This page explains that zone, the Gulf zones beyond the islands, and what the advisories and warnings mean in knots and feet.
One office, one zone
The weather service office in New Orleans/Baton Rouge writes the coastal waters forecast for this coast; its area runs from Pascagoula to the Atchafalaya River, out to 60 nautical miles. It issues a new forecast at least twice a day.
Every town on this board, Waveland to Moss Point, reads one zone:
| Zone | Name | Office | Towns on this board |
|---|---|---|---|
| GMZ532 | Mississippi Sound | New Orleans/Baton Rouge | Waveland, Bay St. Louis, Diamondhead, Pass Christian, Long Beach, Gulfport, Biloxi, D’Iberville, Ocean Springs, Gautier, Pascagoula, Moss Point |
Beyond the barrier islands the Gulf has zones of its own: GMZ557, the coastal waters from Pascagoula to Stake Island out 20 nautical miles, and GMZ577 beyond it, from 20 to 60. Chandeleur Sound, to the south, is GMZ536. If you are going out through a pass between the islands, read both forecasts: the Sound you leave from and the Gulf you are heading into.
A Sound forecast and a Gulf forecast read differently
The Gulf zones give the wind and the seas in feet, and often a Wave Detail line after them: each wave train by direction, height and period in seconds. A short period means close-set waves, steeper for their height.
The Sound is written with the wind first and then the waves in feet (“Waves 1 foot or less”). On the Sound the wind line is the one to read first. When two zones are expected to see the same weather, the office writes one paragraph headed with both names; when they differ, each gets its own.
What the words mean, in knots
These are the National Weather Service’s thresholds. The advisory threshold depends on the region, and New Orleans/Baton Rouge publishes its own; the warning thresholds do not change.
- Small Craft Advisory. In the weather service’s Southern Region, which includes this coast: sustained winds of 20 to 33 knots, or forecast seas of 7 feet or more expected for more than two hours. New Orleans/Baton Rouge states its own criteria for its coastal waters within 60 nautical miles, which take in the Sound: sustained winds or frequent gusts of 21 to 33 knots, or waves of 7 feet or higher, expected to begin within 36 hours. The service says the thresholds are “specific to geographic areas”, and “There is no precise definition of a small craft”: whether your boat and your experience are up to it is your call.
- Gale Warning. Sustained winds or frequent gusts of 34 to 47 knots, not directly tied to a tropical cyclone.
- Storm Warning. 48 to 63 knots, likewise.
- Special Marine Warning. A short warning, usually for up to two hours, for thunderstorm winds or gusts of 34 knots or more, hail of three-quarters of an inch or more, or waterspouts.
- Tropical Storm and Hurricane Warnings. Gale and storm warnings are for wind not tied to a tropical cyclone; for a tropical storm or hurricane these are the warnings. A tropical storm warning means sustained winds of 39 to 73 mph are expected within 36 hours. A hurricane warning is issued 36 hours before tropical-storm-force winds are expected, because preparing becomes difficult once they arrive.
The line most often misread
The office prints the same note at the top of every forecast: seas are given as a range of the average height of the highest third of the waves, with the occasional height of the average highest tenth. So “seas 4 to 6 feet” is not the size of every wave; most are smaller, and some are bigger.
The weather service’s caution: wave forecasts are an average, and some individual waves “can be expected to be as much as two times greater.”
Read a forecast of six-foot seas as one that can include twelve-foot waves.
Sources
- National Weather Service New Orleans/Baton Rouge, marine zone map — the zone numbers and names
- New Orleans/Baton Rouge coastal waters forecast — the office’s area, the Sound’s wording, Wave Detail and the note on seas
- National Weather Service New Orleans/Baton Rouge, watch, warning and advisory criteria — the office’s own small craft advisory criteria
- National Weather Service, marine warning and advisory definitions — the Southern Region thresholds and the warnings
- National Weather Service, marine forecast FAQ — significant wave height and individual waves