South Florida May Rainfall Watch (Lushine Dry May Theory)

[gatorcane]

I want to open up this thread to monitor rainfall across South Florida in May and to have any discussions on this theory (which is inherently controversial). We seem to open a thread like this nearly every year but this May is looking especially dry. According to Jim Lushine of NWS Miami, his study has revealed a potential link between rainfall in May and probability of hurricane activity for South Florida:

Exerpt:

"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."

http://www.insurancejournal.com/news/so ... /54367.htm

May rainfall totals to date at major South Florida terminals:

Miami International: MONTH TO DATE 0.00
Ft. Lauderdale International: MONTH TO DATE 0.00
West Palm Beach International: MONTH TO DATE T

[boca]

I thought it was a good read,but honestly a dry May will have no effect on what happens in Aug thru Oct hurricane season.

[Cyclone1]

Interesting...

[gatorcane]

I thought it was a good read,but honestly a dry May will have no effect on what happens in Aug thru Oct hurricane season.

At first glance you are right. But what Lushine is arguing is not an argument of absoluteness, that is, it's not a statement of "if South Florida receives less than a certain amount of rainfall, it will be hit by a hurricane." What he argues is that looking over historical data, the probability of a hurricane impact on South Florida INCREASES based on the amount of rainfall received in South Florida in May. The amount of rainfall is directly proportional to the rainy season beginning which corresponds to dew point levels maintaining 70F for an extended period of time. The mean start of the rainy season in South Florida is May 21st. Check out this link, which discusses some of these topics in more detail:

http://www.srh.noaa.gov/mfl/newpage/summer_season.html

[KWT]

Its interesting but the prediction for 2005 wasn't really that great though I suppose Opheila sort of fitted the bill...

"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."

Instead we had several hurricanes hit the south florida region, Katrina, Rita came close enough to have some effects and hit the keys and also Wilma smashed thorugh SW Florida.

[MiamiensisWx]

Apparently, another meteorologist at the NWS Miami forecasting office disagrees with Lushine's theory.

http://www.sun-sentinel.com/news/local/southflorida/sfl-flbrainy0507sbmay07,0,3126544.story

"In delivering the summer weather outlook, Molleda noted two cautions: First, the rainy season forecast can be iffy because it is so closely tied to what happens during hurricane season. Second, there is no real correlation between the amount of rain in the spring and how active the hurricane season will be."

He's likely referring to the dry May theory and debunks the correlation between drier south FL conditions and the mean ridge position during the peak of the TC season.

Finally, gator, you have also emphasized that this theory primarily applies to Cape Verde tropical cyclones, and south Florida receives most strikes from the Caribbean.

[gatorcane]

Very little, if any rain expected in the extended forecast as South Florida's extremely dry May continues.

Latest NWS Miami extended:

VERY LITTLE HAS CHANGED IN THE EXTENDED PORTION OF THE FORECAST
THIS MORNING...WITH A BRIEF PERIOD OF SLIGHTLY COOLER AND DRIER
CONDITIONS EXPECTED ON TUESDAY. LOW-LEVEL FLOW WILL VEER TO
THE NORTHEAST AND EVENTUALLY EAST FROM LATE TUESDAY INTO WEDNESDAY
MORNING...SETTING THE STAGE FOR LOW-LEVEL MOISTURE TO SPREAD BACK
OVER THE AREA BY THE END OF THE WEEK. MEANWHILE...THE GLOBAL MODELS
ARE IN FAIRLY GOOD AGREEMENT ON UPPER-LEVEL RIDGE AXIS BECOMING
ESTABLISHED ACROSS FLORIDA DURING THIS PERIOD...DOWNSTREAM FROM A
LARGE UPPER LOW THAT IS PROGGED TO DEVELOP OVER THE GREAT LAKES. THIS
WILL MAINTAIN WARM AND DRY CONDITIONS ACROSS THE AREA THROUGH THE
END OF THIS FORECAST PERIOD.

[Nimbus]

Its possible that the mean ridge position shifts east later in the season often enough to create a statistical anomaly. South Florida has had a string of good luck when it comes to dodging major storms lets hope it continues..

[Sanibel]

Not a drop of rain yet in May here. We have a front due Monday night with thunderstorms predicted.

[Blown Away]

Very dry May for SFL so far.

[MiamiensisWx]

The dry May theory has been debunked. See my previous post above.

"Apparently, another meteorologist at the NWS Miami forecasting office disagrees with Lushine's theory.

http://www.sun-sentinel.com/news/local/southflorida/sfl-flbrainy0507sbmay07,0,3126544.story

'In delivering the summer weather outlook, Molleda noted two cautions: First, the rainy season forecast can be iffy because it is so closely tied to what happens during hurricane season. Second, there is no real correlation between the amount of rain in the spring and how active the hurricane season will be.'

He's likely referring to the dry May theory and debunks the correlation between drier south FL conditions and the mean ridge position during the peak of the TC season.

Finally, gator, you have also emphasized that this theory primarily applies to Cape Verde tropical cyclones, and south Florida receives most strikes from the Caribbean."

Additionally, Lushine mentioned that several tropical cyclones have struck south Florida during a "very dry" May. What defines "very dry"? Is it a month with <1 inch of precipitation? We need an actual benchmark.

[JonathanBelles]

Nothing at all here in May yet.

[MiamiensisWx]

Its possible that the mean ridge position shifts east later in the season often enough to create a statistical anomaly. South Florida has had a string of good luck when it comes to dodging major storms lets hope it continues..

Huh? Did you forget Wilma's Category 3 landfall on the Gulf side and its serious effects across the state? In my view, it doesn't matter whether the TC strikes on the east or west side if it still causes significant damage.

South FL is not "overdue".

[Blown Away]

MiamiensisWx: I don't think Lushine said it was scientific evidence. He just pointed out a correlation between dry SFL May's and SFL hurricanes. I agree w/ you we need to look at the years Lushine used in his study to determine what is considered a dry SFL May. Dry SFL May's may indicate a stronger Bermuda High, walk outside today and we can see a strong BH in effect.

[MiamiensisWx]

Lack of precipitation does not necessarily indicate a ridge. There has not been a strong ridge at the H5 level, which steers tropical cyclones. In fact, the low level ridge (which does not influence mature tropical cyclones) has been very weak. There simply has not been a persistent easterly flow at the surface. The main reason for the dryness is a persistent inversion that has inhibited convection. If that were not present, we would have been drenched by diurnal convection moving west to east across the state. It has been southwest flow city for most of the month here.

There was also two wet Mays (1947 and 1949) that featured a Cat 4 and Cat 3 hurricane of Cape Verde origin strike the SE coast of FL, respectively.

I'm also tired of stupid "overdue" arguments for any state.

Finally, meteorology is a science, so Lushine's argument must be based on actual science if you consider his theory as valid.

[MiamiensisWx]

MiamiensisWx: I don't think Lushine said it was scientific evidence. He just pointed out a correlation between dry SFL May's and SFL hurricanes. I agree w/ you we need to look at the years Lushine used in his study to determine what is considered a dry SFL May. Dry SFL May's may indicate a stronger Bermuda High, walk outside today and we can see a strong BH in effect.

You're wrong; Lushine needs to specify the qualifications of a "very dry" May. For example, is it a May with less than 1 inch of measurable precipitation?

[Blown Away]

MiamiensisWx: I agree w/ you on the "overdue" talk. If your going to use that talk, no way you can even begin to say that the Florida Peninsula is overdue. Since 04': Charley, Frances, Jeanne, Katrina, Wilma; close calls from Rita, Noel, and the TD in 06' (name?), TS in Tampa (name?). That's amazing activity.

[MiamiensisWx]

MiamiensisWx: I agree w/ you on the "overdue" talk. If your going to use that talk, no way you can even begin to say that the Florida Peninsula is overdue. Since 04': Charley, Frances, Jeanne, Katrina, Wilma; close calls from Rita, Noel, and the TD in 06' (name?), TS in Tampa (name?). That's amazing activity.

...and the "odds" of a strike do not increase or decrease depending on an area's recent history. The odds always remain the same each season.

I'm just very skeptical of the dry May theory because we do not have accurate upper air data for many of those hurricane seasons, including 1935, 1992, 1965, and many pre-late '70s seasons. In other words, there's no way to "prove" that the hypothesis regarding the supposed mean ridge placement correlation ever verified...

[Blown Away]

MiamiensisWx: I don't think Lushine said it was scientific evidence. He just pointed out a correlation between dry SFL May's and SFL hurricanes. I agree w/ you we need to look at the years Lushine used in his study to determine what is considered a dry SFL May. Dry SFL May's may indicate a stronger Bermuda High, walk outside today and we can see a strong BH in effect.

You're wrong; Lushine needs to specify the qualifications of a "very dry" May. For example, is it a May with less than 1 inch of measurable precipitation?

Your right, his study, he needs to specify the qualifications. I thought we could look up the info since he is retired, I know I want to be left alone if I can ever retire.

[CourierPR]

When Andrew struck south Miami-Dade County in 1992, south Florida had one of its driest Mays on record. I do agree about the overdue talk, but let's all prepare for the worst and just watch what happens during the season.