The forecast comes in at 0615 over VHF channel WX-2, the same male voice that has read it for two years now, a recording stitched from segments by a text-to-speech engine the National Weather Service introduced in 2022. The voice says: Coastal waters from Stonington Maine to Merrimack River out 25 nautical miles. Today. South wind 10 to 15 knots, becoming southwest 15 to 20 with gusts to 25. Seas 3 to 5 feet. Visibility 1 to 3 nautical miles in fog. Showers likely.
Donald Pesce, who retired from the Coast Guard Atlantic Strike Team in 2019 and now teaches a Saturday morning forecast-reading class out of the South Portland community boathouse, listens to that recording in the same posture every morning. Elbows on the kitchen counter, coffee at the right hand, weather book open to the day's blank page.
He says the vocabulary is the first thing to get past. Most weekend skippers, in his experience, can recite the wind speeds back but cannot tell him what becoming means in a forecast sentence. Becoming is not a synonym for shifting. Becoming carries a time hint, usually six to twelve hours, and it implies the new direction will hold once it arrives.
Variable is the word that should worry a small-boat operator more than strong. Variable wind in a marine forecast usually means a frontal passage is fighting the prevailing flow, and the period of confusion can produce square seas, no clean direction, white horses in every quadrant.
Pesce has a hierarchy of advisories he writes on the chalkboard at the boathouse. Small Craft Advisory at 25 to 33 knots sustained or seas 7 feet or higher. Gale Warning at 34 to 47 knots. Storm Warning at 48 to 63. Hurricane Force Wind Warning at 64 and above. The numbers are universal across the United States; the seas thresholds vary by zone.
What changes in practice is what each advisory means for a 26-foot fiberglass center-console with a single Yamaha outboard. A Small Craft Advisory in Casco Bay is a real warning. The same advisory off Cape Hatteras is, for many local skippers, a working condition.
The class returned to the chalkboard often during a March session this year, when a forecast for the Penobscot Bay zone read showers likely with seas of 4 to 6 feet and visibility 1 to 3 nautical miles. One of the students, a man who keeps a Cape Dory 22 at Belfast, asked why the forecast did not say thunderstorms. Pesce explained that the NWS reserves thunderstorms for conditions where the Storm Prediction Center has issued a convective outlook, and that showers in a marine forecast can still include lightning if the outlook does not warrant the upgrade.
Visibility deserves its own paragraph in any class on marine vocabulary. The forecast gives a number in nautical miles, and below one nautical mile the language shifts to dense fog advisory. Most small-boat operators, Pesce has found, underestimate fog. They believe radar makes them safe. Radar does not make them visible to the lobster boat that has not turned its own unit on.
The wind speed itself comes in two forms: sustained and gusts. NWS marine forecasts give a sustained range and then a gust value if the gust factor exceeds about 1.4 times the sustained mean. Pesce tells the class to plan for the gusts, not the sustained. A boat that handles 20 knots sustained will be tested by a 30-knot gust, and the gust is what lays the boat over.
There is a temporal grammar to the forecast that the class learns slowly. Tonight in the marine product begins at 6 p.m. local. Today ends at 6 p.m. The transition is the riskiest part of any day on the water in spring, because the convective potential peaks in the late afternoon and the forecast language often pivots without changing the wind speed numbers.
The April class had a guest, Annette Vorhees, who flies a NOAA G-IV reconnaissance aircraft into hurricanes for a living. She told the students that the forecasters writing their morning marine product are using output from the same models she helps validate, and that the language those forecasters choose is sometimes the only signal the model uncertainty makes it into the public product. Becoming is a hedge. Likely is a hedge. Probable is a stronger hedge.
Pesce keeps a binder of forecast transcripts going back to 2008, indexed by the day's marine casualties in his zone. He uses it as a teaching tool. The class looks at the forecast for July 19, 2014, the day a 24-foot bowrider out of Cape Porpoise capsized in a line squall, and they read the words that preceded the casualty. The words were not hidden. Isolated thunderstorms possible after 3 p.m.
Possible meant 20 to 30 percent probability, in NWS internal practice. The skipper of the bowrider, who survived, told the Coast Guard he had read the forecast and concluded the chances were too low to cancel. Pesce uses the case study not to second-guess but to argue that probability words in a marine forecast deserve more weight than weekend boaters often give them.
A separate vocabulary applies to the offshore product, which extends from 25 nautical miles to about 250. The offshore product uses seas the same way as the coastal but introduces swell period, given in seconds, which the coastal product rarely includes. A 10-second swell period and a 4-foot wind wave produce a very different ride than a 6-second swell of the same height.
The High Seas product, written for vessels well offshore, drops most of the friendly language entirely. It is a telegraphic format inherited from the days of weather facsimile, with positions given as latitude-longitude pairs and pressure gradients implied by the spacing of isobars on the chart the operator is presumed to be reading alongside the text.
Most weekend skippers, Pesce concedes, will never need the High Seas product. They need to read the coastal waters product correctly. He tells them to listen for three things every morning: the wind direction trend, the visibility floor, and the gust factor. Those three numbers determine whether a trip is on or off.
He tells them to listen a second time at midday. Marine forecasts update at roughly 4:30 a.m., 10:30 a.m., 4:30 p.m., and 10:30 p.m. local, with intermediate updates as conditions warrant. A morning forecast that reads benign can become a small-craft afternoon by lunch. The intermediate updates are not given fanfare, and the broadcast voice does not announce this is an update. The skipper has to notice.
After two years teaching the class, Pesce has seen patterns in who returns and who does not. The skippers who return for the advanced session, which covers the GFS and the European model and the difference between the two for short-range marine forecasting, are usually the ones who already lost a boat or nearly lost one.
He does not consider this a failure of his teaching. He considers it a feature of how adults learn weather. Most of the time, the forecast is accurate enough that an inattentive skipper gets home fine. The forecast is a structure that catches the cases where inattention would otherwise be expensive.
On the last Saturday of the April session, the forecast for the local zone read west wind 10 to 15 knots, seas 2 feet or less, visibility unrestricted, sunny. Pesce dismissed the class fifteen minutes early. He told them to go sail. They had spent the morning translating language; the afternoon belonged to weather that did not need translation.
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