S. Fla. Forecaster Suggests Link Between Hurricane Behavior, May Rainfall

April 28, 2005

A link between the behavior of hurricanes and the amount of rain that falls in South Florida in May has been suggested by Jim Lushine, a meteorologist and weather forecaster at the National Weather Service in Miami.

Lushine, who has predicted South Florida weather for 33 years, told the South Florida Sun-Sentinel he suspects there is a link between May rainfall and the chances of hurricanes striking South Florida.

When rainfall in May exceeds the regional average of 5 inches, he said the risk decreases. But when rainfall is less than normal, the likelihood of a strike increases. “It’s kind of the lynchpin on whether it will be an active season for us,” Lushine explained.

His outlook for this May: Perhaps normal, which Lushine said could mean some close calls for South Florida. He is quick to note that there are no guarantees. But bolstering his theory, last May turned out to be a very dry month, with just 2 inches of rain.

In contrast, May 2003 dumped a whooping 14 inches of rain on the area and, if Lushine’s theory holds water, shielded the region from what was an even more active hurricane season than last year’s, which produced 15 named storms.

Of the 16 named storms in 2003, only Tropical Storm Henri bothered Florida, and just barely. By the time it crossed Central Florida, Henri was just a pesky tropical depression.

“These are two extremes, with 2003 being great for us and 2004 being terrible for us,” Lushine said. “What usually happens is something in between those kinds of patterns, and that’s the kind of pattern we’re in right now. It looks like this May could be a ‘tweener’ year.”

That could mean the six-month 2005 hurricane season, which begins June 1, may be reminiscent of the 1999 season, when a parade of storms marched toward Florida but veered north before striking. The most memorable example was Floyd, a behemoth that taunted Florida’s east coast before slamming the Carolinas.

Like all hurricanes, Floyd’s path was controlled by the transient low and high pressure systems in the atmosphere, the same lows and highs that influence South Florida’s rainfall.

When they’re near, low-pressure systems generally protect Florida during hurricane season. Spinning counterclockwise, the same direction as a hurricane, they push storms away. Lighter in weight, they also allow air to rise, producing more rain–hence, the correlation Lushine found between rainy Mays and fewer hurricanes.

Conversely, high-pressure systems blow clockwise, blocking hurricanes from changing course. Heavier in weight, they also cause air to sink, producing less rain.

So, what makes May so special in determining hurricane activity?

May, Lushine said, usually marks the transition between South Florida’s two seasons, wet and dry and the pressure patterns present during the month often persist.

“May controls our rainy season, and something that is strong enough to cause the rainy season to come earlier or later is strong enough to last the whole season,” he said.

Lushine first noticed the link between dry Mays and increased hurricane probabilities in South Florida in 1992, the same year Hurricane Andrew, a top-of-the-chart Category 5, leveled much of south Miami-Dade County. That May proved to be the second driest on record, producing only 0.9 inches of rain.

The driest May, with 0.6 inches of rain, Lushine found, came in 1965, the year Hurricane Betsy, a major Category 3 storm, swamped the upper Keys.

Lushine told the Sun-Sentinel he didn’t notice the coincidence until Andrew struck. Then he started reviewing May data, finding the third driest May in 1935, when the Labor Day hurricane, the strongest on record to hit the United States, slammed into the Florida Keys.

Plotting 75 years worth of May rainfall data, Lushine found the probability of a hurricane striking South Florida almost tripled after a very dry May. Conversely, the chances of a hurricane striking South Florida after a wet May were three times less.

Some are skeptical, but after 42 years with the weather service, Lushine, 60, has enough faith in his May theory that he pins his retirement on next month’s rainfall. “If it’s wet, I’ll stick around to the end of September,” he said. “If it’s dry, I’m going to wave bye-bye and head to Alaska.”

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Latest Comments

  • June 3, 2005 at 5:43 am
    Keys Treasures says:
    So.... How did this May rank on the Rainy Scale?
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