S Florida and May Rain Fall

[Windtalker]

A rainy May theory: The wetter, the better

By Maya Bell
Miami Bureau
Posted April 27 2005

MIAMI -- Just about everybody knows that April showers bring May flowers, but weather forecaster Jim Lushine has discovered something just as commendable about rainy Mays: They might ward off hurricanes.

During 33 years of predicting South Florida's weather, Lushine, a meteorologist for the National Weather Service in Miami, has found a link between May rainfall and the chances of hurricanes striking South Florida.

When May rainfall exceeds the regional average of 5 inches, 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 said.

His outlook for this May: perhaps normal, which Lushine said could mean some close calls for South Florida.

Lushine 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.

And lest anyone need any reminders, an unprecedented four hurricanes struck Florida last year. Two storms, Frances and Jeanne, made landfall in southeast Florida, near the St. Lucie and Martin county line.

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 said he didn't think much of 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 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. Others are skeptical, but after 42 years with the weather service, Lushine, 60, has enough faith in his May theory that he plans to pin 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."

[Aquawind]

We have a good soaker going on right now..although I see the forecast finally has a few days above 70 for morning lows..now that is Florida weather. The lawns actually did start showing some dry spots till last night..something that is expected this time of year..I will be hoping for lots of rain in the next month...it can still be a busy season..hopefully a busy fishy season..

Paul

[gatorcane]

We are seeing brush fires already in Palm Beach County

[Javlin]

Well someone on this board was trumpeting this idea early on to get thumped in the head for it.It makes sense since we live in a fluid enviroment like the atmosphere that is forever changing slowly.

[The Big Dog]

We are seeing brush fires already in Palm Beach County

Yeah, well, there's some suspicion that those fires were set. It's really not very dry in the state right now. A little at the south tip maybe, but not the rest of the state.

http://flame.fl-dof.com/fire_weather/kbdi/

[cyclonaut]

Let see what May brings.

[EDR1222]

That information about the weather patterns in May is kind of interesting. It will be very interesting to see how it plays out with May right around the corner since April, so far has probably been a little wetter than normal, at least in Central Florida.