Using forecast charts of Brazil provided by the National Weather Service, a small weather consulting firm in Suitland, Md., figured a big freeze was in store for a large part of the country's coffee crop, and notified its client, a commodities trader in coffee beans. The trader held on to his bean supply and, after freezing temperatures ruined much of the crop, sold it at a huge profit when the price of beans surged.

"With commodities, you're looking at the weather factor, which is valuable information when you decide to sell or buy," said Saul Hirsch of Intercon Inc., the Suitland firm, whose clients include commodity brokers in New York and Chicago. "The need for rain, a dry period, a premature freeze will have a very dramatic impact. If you anticipate these facts, you can make money."

Hirsch and three other meteorologists retired from the National Weather Service six years ago to form Intercon, located near the federal World Weather Building in Camp Springs, Md. While the company's clients vary, seven-day forecasts for commodities traders are its specialty.

"We're a small company," Hirsch said. "We try to find a niche in the market we can exploit."

Once mainly the purview of the federal government, weather forecasting has fallen more and more into the hands of private consultants whose clients need specialized weather information beyond the general public forecasts offered by the NWS.

Demand for forecasts and interpretations of weather data by the nation's 3,000 private meteorologists has created a $100 million industry, according to NWS figures for 1984. The market's growth began in 1983, when the NWS, part of the U.S. Department of Commerce, announced its gradual switch from teletypes to high-speed, computerized equipment to transmit temperatures, wind speeds and other weather information.

The change helped create a weather-data industry, which has grown from one or two companies in 1983 to about 25 today. Now, along with satellite photos and maps from the NWS, weather consultants get the specific weather information they need from the data companies simply by using a phone, a modem (a device that allows a user to connect his telephone to a computer) and a minicomputer.

"The private sector has taken over predicting local weather," said Michael Garstang of Simpson Weather Associates in Charlottesville. "The National Weather Service is now concerned with large-scale forecasting, not the local situation. Consultants are better; they can be more specific."

Most weather consultants work for small companies, and attract business either by word of mouth or through listings in journals such as the Bulletin of the American Meteorological Society. Some work for large aerospace companies such as Lockheed Corp. and Boeing Co., while others work on short-term contracts for clients such as airlines, public utilities, federal agencies, restaurants, the media and trucking, shipping and film-making companies.

Simpson Weather Associates, which grossed $1 million in 1984, is staffed by five professors of environmental engineering at the University of Virginia, who research and make recommendations on weather trends based on mathematics and computer modeling.

Last year, the company received $100,000 from the state of Florida to figure, by analyzing records of past storms, when hurricanes are likely to occur, allowing state officials to decide when to proceed with costly evacuations. And from 1981 to 1983, the company charged the University of Maryland $120,000 to study the potential for wind energy in the West Cumberland area.

"It's a very laboratory-intensive activity we're in. Our product is ideas on paper, not material things," Garstang said. "We're relatively small. The profits go to paying salaries."

William Haggard, whose Climatalogical Consulting Corp. of Asheville, N.C., specializes in forensic work, said most of his clients are in the aviation business. Forensic meteorologists mostly do research to help lawyers prepare for cases rather than testifying in court themselves, he said. Pan American World Airways once hired him to study records of wind conditions during the crash of one of its aircraft in New Orleans, in a dispute that was settled out of court.

"You work closely with your client and do your homework carefully because opposing clients can make their lawyers ask good questions," Haggard said. "Anyone who is sloppy won't last long."

Irving Krik, 78, is perhaps the granddaddy of weather consultants. The premier weather forecaster for the film and airline industry in the 1930s, Krik was Gen. Dwight D. Eisenhower's weatherman for the 1944 D-Day invasion and for Allied bombings of Germany during World War II. After the war, he devised a controversial method of long-range forecasting, using decades-old records to predict weather years in advance. His small company, Irving Krik Associates of Pasadena, Calif., (1984 gross: $1 million) claims 80 to 90 percent accuracy for single-day forecasts months ahead and for seasonal forecasts five years or more in the future.

Krik's fees range from $100 to forecast the weather on a wedding day to $100,000 per year to forecast rainy seasons for hydroelectric companies. His company boasts that it has forecast weather for inaugural committees from Eisenhower's to Carter's, the 1960 Winter Olympics Committee, the government of Sardinia, and Lady Bird Johnson, a longtime client who hired Krik to predict the weather for a day this September when she plans an outdoor party for former ambassador Averill Harriman in Middleburg, Va.

Some of the larger weather companies have dozens of employes and combine both forecasting and data services. One is the Murray and Trettle Co. of Northfield, Ill., which provides daily forecasts for most movie companies that shoot films in the Chicago area. It also warns the Brachs Candy Co. about high temperatures to save chocolates from melting and discoloring during shipment.

Weather Service International of Bedford, Mass., is probably the nation's largest data service, and includes among its clients the European edition of USA Today. The firm and its forecasting business, Weather Services Co., grossed $10 million in 1984, according to WSC President Paul Leavitt.

WSI's biggest clients are in the media and noncommercial aviation. WSC tailors forecasts for clients in agriculture and other industries at fees ranging from $60 to $100 per hour, Leavitt said.

Some clients, such as local governments, keep WSC consultants on retainer to warn them of weather extremes so that they know, for instance, when to send out workers to remove snow from city streets.

Earnings of weather consultants vary with expertise and experience. The median salary for private meteorologists was about $36,000 in 1983, according to NWS estimates. Forensic meteorologists charge about $70 per hour. An experienced consultant hired to predict rainfall levels for a dam project can command $200 to $400 per day plus expenses.

The best paid, however, are the nation's approximately 500 radio and television weather forecasters, whose salaries average about $40,000 but whose total compensation from all clients can be as high as $300,000 for some of the best-known cable and network personalities.

Gordon Barnes, weatherman for WDVM-Channel 9 in Washington, supplements his income by making regular, on-air forecasts for eight radio stations, one as far away as Arkansas, via telephone from his home. Barnes bases his forecasts on NWS surface maps, sent by satellite, that he gets from a facsimile machine at home, and on information from a weather data service he reaches by phone. The maps provide information on wind speeds, cloud cover and rain or snow in the specific areas for which he makes his forecasts.

"The secret to success is to make your own forecast," said Barnes, a native of Bermuda and a former meteorologist for Pan Am. "Some people believe that you have to be in the location to make a forecast, and that's not true, as long as you understand the weather peculiarities of a certain area."

While the NWS offers greater access to its weather observations, some say the federal government also should cut back some of its forecast services, such as the frost and freeze warnings it issues to benefit farmers and cattle ranchers. So far, Congress has blocked that proposal.

But if it does happen, the private sector is well-equipped to pick up the service, and not necessarily at extra cost to the weather-conscious, others say.

The public gets weather information "mostly from radio, television and newspapers," Leavitt said. "If the government took any of its services away, the radio and TV stations would pick up the information as a service to listeners."