The article presents information on how weather can affect human health. The weather's power over health was demonstrated dramatically several times in the space of just a few weeks in 1999. In three states along the U.S. East Coast, weeks of drought and intense heat created ideal breeding conditions for mosquitoes that turned out to be carrying an encephalitis virus never before seen in the Western Hemisphere. In Asia, from China to the Philippines, torrential rains during an unusually severe monsoon season unleashed floods, leaving thousands dead and compromising water supplies and already weak sanitation systems. INSET: TODAY'S FORECAST: INCREASED COLD AND HEART ATTACKS.