Weather

Annotation

Text Forecasts are prepared by meteorologists and present a summary of their outlook in familiar formats. The NOAA Coastal Waters forecast is identical to the broadcast on NOAA weather radio. The NWS Boston forecast is shore-focused but useful for coastal daysailing.

Graphic Forecasts present computer model output without the interpretation of meteorologists. The hourly graphs are lovely in their simple design and condense a lot of information on a single page. Interactive maps are a little fussier to use, but give a more regional picture. The Sailflow map starts with the same computer output as the NWS maps, then adds more coastal weather observations and runs everything through a finer-grained model. I haven't used it enough yet to comment on its claims of greater accuracy, but the area covered at higher resolution isn't broad enough for cruise planning.

Surface Analysis gives a classic weather map style snapshot of recent wind, pressure, temperature and fronts. The HPC Northeast US analysis is updated every 3 hours, so the data is usually only 2-5 hours old. It gives a nice feel for the regional systems controlling the days weather. The (Near) Realtime Mesoscale Analysis is a nice computer-generated best estimate of regional winds, updated hourly.

Forecast Charts combine meteorologists' evaluation of the various computer models into familiar maps that look ahead several days. The zoomed out scale makes them useful mostly for anticipating broad trends and well-defined storms.

Computer Models are the backbone of modern weather forecasting. The primary American models are GFS (Global Forecasting System, a worldwide model of relatively lower resolution, with output data points approximately 30 miles apart.) and NAM (North American Mesoscale, a continental and near-coastal model of relatively higher resolution, with output points less than 10 miles apart). Forecasters in Boston seem to more often prefer the GFS solutions for coastal weather. The charts linked here show sea-level pressure (implying wind) and rainfall. The resolution of the graphics for both models is too course to be useful for any detailed do-it-yourself forecasting, but they give a great sense of the big picture. The model output also includes a lot of mid and upper atmosphere stuff that's completely esoteric to us laymen.Try the NCEP model index page if you want to peek behind the curtain.

Grib forecasts (for "gridded binary") can include any weather data, though most commonly it's the raw output of computer models, packaged as an array of data points. Depending on the source, these points can be separated by a degree, half a degree or in some instances less. The worldwide model outputs, describing the atmosphere top to bottom, represent gigabytes of data. A handful of companies repackage this data for individual use - sometimes free, often fee-based. By selecting a small number of data types (say surface windspeed and direction) and a small area (say New England coastal waters) the user can get a forecast tailored specifically to their needs in a file of only a few kilobytes. This makes grib forecasts especially suited for low-bandwidth downloads. Viewing grib files requires special software that can be purchased from grib providers or found in many navigation packages. Grib.US offers a free (requires login) basic viewing program for Windows and a simple interface to download wind, pressure and precipitation data for a chosen area. OCENS offers the widest range of available grib data, although it requires expensive software, an annual subscription, and fees per download.

Radar and Satellites provide near-realtime images of clouds and rain. Radar is especially good for tracking squalls. The Upton, NY radar gives a look further ahead in most weather patterns.

Buoys and Shoreside Observations are also near-realtime and they're spread out pretty effectively along the coast. A good reality check on the forecast. Dial-A-Buoy lets you get reports by cellphone.

The Discussions are pretty thick with abbreviations and technical jargon, but with a little work they're not impenetrable. Most useful for getting a sense of how confident the forecasters are about their predictions.

Most of the links listed above go straight to the relevant data, with a minimum of click-through. Under Centers are links to the home pages of the various agencies that provide these forecasts and data.

The National Hurricane Center actively tracks any tropical storms with a nice graphic and written discussions.