BY MARTIN MERZER

  A hurricane was under construction Wednesday in the Caribbean, and though the threat to South Florida diminished -- but did not disappear -- the
  threat to Cuba intensified sharply.

  So forecaster Richard Pasch picked up a telephone, punched in 13 digits, tried again, tried a third time and finally got through. He manifested a sense of
  urgency.

  A storm called Isidore was expected to hit the western end of Cuba tonight and Friday as a hurricane, and it could be bad. Then, as it moves through the
  Gulf of Mexico, Isidore could clip the Florida Keys and its squalls could reach Miami-Dade and Broward counties.

  Lives were at stake, in Cuba and possibly soon in Florida or elsewhere in the United States, so international grievances and tensions were temporarily
  set aside.

  At 9:46 a.m. Wednesday, an American forecaster called a Cuban forecaster and they began working together.

  ''The atmosphere doesn't know anything about frontiers,'' José Rubiera, head of Cuba's Institute of Meteorology, later told The Herald.

  ''We have to have help from Cuba,'' said Max Mayfield, director the National Hurricane Center in West Miami-Dade County. ``They have information that
  can help us, and we can help them.''

  The cooperative effort to protect people from hurricanes inspired the phone call.

  ''Hello? Hello?'' Pasch said. ``Yes, this is Richard Pasch in Miami. At the National Hurricane Center. El Centro Nacional de Huracanes. Yes. José? Is this
  José?''

  On the other end, Rubiera came on the line. Under international agreement, U.S. forecasters coordinate hurricane warnings throughout the region, but
  Cuba is responsible for issuing its own alerts.

  Pasch spoke slowly and loudly through a static-filled connection. ''We understand you want to issue a hurricane watch,'' he said. ``For which provinces?''

  Speaking in English, Rubiera told him: Pinar del Río, the Isle of Youth, the province and city of Havana, Matanzas, pretty much all of western Cuba.

  ''OK,'' Pasch said. ``We'll get it out at 15Z.''

  ''Z'' is meteorology-speak for Zulu or Greenwich Mean Time -- in this case, 11 a.m. EDT.

  And there it was, on the next official advisory from the National Hurricane Center:

  ``At 11 a.m. EDT, 1500Z, the government of Cuba has issued a hurricane watch for western Cuba, from the provinces of Villa Clara and Cienfuegos
  westward, and including the Isle of Youth.''

  That meant winds of at least 74 mph were possible within 36 hours. The watch was upgraded Wednesday night to a warning, meaning that hurricane
  winds were expected within 24 hours.

  Tropical storm warnings were in effect for the Cayman Islands and Jamaica, whose residents endured a thorough soaking Wednesday.

  Mayfield also came on the line, trading impressions of the storm with Rubiera, thanking him for helping to clear the way for flights by U.S. Hurricane
  Hunter aircraft through Cuban airspace.

  Mayfield and Rubiera have met at meteorological conferences, and their forecasters have become familiar with each other in recent years, but their
  interaction is rarely seen in public.

  ''I think I get more Christmas cards from Cuban meteorologists than from my own staff,'' Mayfield said.

  Hurricane Hunter missions such as those flown Wednesday and consultations with Cuban meteorologists, acknowledged to be among the world's best,
  helped Mayfield and his forecasters get a better handle on Isidore.

  The storm was expected to reach Cuba today with its outer edge and make landfall Friday as a Category 1 hurricane -- with winds between 74 and 95
  mph -- though it could become stronger. Rubiera said he predicted about eight inches of rain and some flooding and wind damage.

  ''We are prepared,'' he said.

  Long-term projections suggested that Isidore then would take a more northwesterly course than previously believed, moving into the Gulf of Mexico as a
  Category 2 hurricane but at an angle that could keep its core and much of its rain away from South Florida.

  Forecasters began speaking in terms of inches of rain in South Florida, rather than feet. If the region is lucky, no serious wind will reach Miami-Dade and
  Broward.

  ''I'm feeling a lot better than I did yesterday,'' Mayfield said, ``knowing that I don't have to put up my shutters, at least for now.''

  South Floridians' good fortune could mean misfortune for someone else. When a storm moves into the Gulf of Mexico, it has to make landfall somewhere,
  and Isidore could grow into a large, powerful presence.

  Its most likely destination appeared to be the coast of Texas or Mexico, Mayfield said, but not until next week -- and not for sure.

  He emphasized that long-term projections are inherently subject to error, and atmospheric steering currents are extremely uncertain. It was too early to
  draw any conclusions.

  So, state and local emergency managers remained on alert.

  They noted that only a small change in the projected course could bring Isidore over the Keys.

  ''We're definitely eyeballing this one very carefully,'' said Mike Stone, a spokesman for the Florida Division of Emergency Management. ``The Gulf waters
  are so warm that these storms can go to hurricane strength in a matter of hours.''

  Mayfield and other forecasters agreed that Isidore had excellent growth potential. Atmospheric conditions favored strengthening, and it was crawling
  through water so warm it was ''like high-octane fuel,'' Mayfield said.

  And that, he said, made Wednesday's cooperation with Cuban meteorologists extremely important.

  ''Anything that moves through the Caribbean toward Florida has to go over Cuba,'' he said. ``We can't do a good job without their help. Who knows?
  Maybe this will help political relations between our two countries.''

  Herald staff writers Phil Long and Renato Pérez contributed to this report.