It ended a relatively tranquil quarter-century and marked a return to hurricane seasons of the 1940s, '50s and '60s - more hurricanes, and more powerful storms.

The change was dramatic from 1994 - the last season of the quiet period with only three hurricanes and no major storms of Category 3 or higher - to 1995, a season bulging with a dozen hurricanes and five of those becoming major storms.

``You might expect a gradual transition, but it looks like it made a quick jump,'' said Chris Landsea, a scientist with the National Hurricane Research Division in Miami.

Scientists know hurricane seasons go through cycles lasting decades producing few hurricanes, then switching to periods of more intense activity. From 1940 through 1969, there were 182 hurricanes, with 88 of them growing into Category 3, 4 or 5: the major storms that cause the worst damage.

From 1970 to '94, there were 123 hurricanes and only 38 major storms.

The nine years from 1995 through 2003 saw 69 hurricanes, with 32 reaching Category 3 and higher, only six fewer than the previous 25 seasons.

We are in the 10th season of an active period.

It could last until today's infants are college graduates or longer.

``This could keep going for 15, 20 or 30 years,'' Landsea said.

More storms and more strong hurricanes mean more chances of them hitting land, but that does not translate into 30 more years of punishment like this year for Florida, said Max Mayfield, director of the National Hurricane Center.

``To think Florida is going to continue to be hit by four hurricanes a year is unlikely,'' he said.

The last time a state had been hit by four hurricanes in one year was 1866, when Texas wore the bull's-eye.

Mayfield said broad, large- scale conditions that change slowly may determine active and quiet seasons, but individual storms are guided by ever shifting, smaller-scale conditions.

Scientists can recognize the symptoms but don't necessarily know the cause of such changes in hurricane activity.

Something happens to a major Atlantic current that carries warm water from the tropics northward to Greenland where it cools, sinks and heads south again deep under the surface.

``It flows strong for 25 or 30 years, then weakens. We're not sure why,'' said Phil Klotzbach, a research associate at Colorado State University who works with William Gray, a professor who has studied storms and issued forecasts of hurricane seasons for more than 20 years.

There are two major results of this change. Water in the Atlantic grows a crucial 1 degree or so warmer, and winds 8 miles high blowing from the west decrease.

Though the temperature change seems small, warmer water over thousands of square miles provides higher octane fuel for hurricanes. The lack of high-level winds means less shear that can weaken or destroy storms, which Klotzbach said may be more important than the temperature change.

In calm cycles, the opposite occurs. From 1969 - the final year of an active period - to 1970, the first of a quiet time, water temperature in the tropical Atlantic dropped 1.5 degrees, Klotzbach said.

Why, however, is not so clear.

``We do know the Atlantic flip-flops. Exactly why is still a bit of a mystery,'' Landsea said.

Without knowing why these major changes occur, it's impossible for researchers to know when the Atlantic will go from belligerent back to benign.

``It would be nice to know that two or three years in advance of when it will shift, but we're still a ways off from that,'' Klotzbach said.

Reporter Neil Johnson can be reached at (352) 544-5214.