TODAY IN THE TROPICS A plume of Saharan dust is controlling the tropical Atlantic from Africa to the islands. Meanwhile, El Niño-driven hostile upper-level winds cover the Caribbean. Tropical disturbances are moving off Africa on schedule, but they can't develop without any conducive atmosphere in their path. The cooler-than-normal ocean waters are also a big negative factor. Long-range computer models continue to show an empty slate well into August. This season seems