South Florida May Rainfall Watch (Lushine Dry May Theory)

[Nimbus]

We are assuming that the statistical anomaly is due to the mean ridge position steering Cape Verde storms toward the east coast of Florida and blocking them from turning north. You would need to see more data before drawing the conclusion that the mean ridge position can be forecast from its preseason position. We don't have 1000 years worth of data to analyse.

[Sanibel]

Don't be too harsh on people saying overdue. If the archives show a cyclone hitting a certain place on a 20 year average and one hasn't happened there in 40 years then technically it would be correct to say "overdue," though it is true that averages occur over much longer periods and change according to changes in climate etc.

What I think irritates the skeptics the most is that there is some statistical validity to it. You don't really need a cut-off point on what you would call dry, all you need is a graph to show a relation between more dryness and more cyclones.

[MiamiensisWx]

Sanibel, you can be "statistically" overdue based on previous climatological return periods (as you mentioned), but the chances for a hit never increase or decrease. This has been repeatedly hashed out in many threads.

I'm sorry, but since the dry May theory relies on science, it should be subject to the same scientific scrutiny.

[gatorcane]

Latest NWS Mia snippet. But latest radar imagery suggests there is much more energy in the atmosphere than this forecast is suggesting with strong to scattered storms now developing along the Eastern Palm Beach County coast as the strong SW winds are starting to collide with a seabreeze trying to form. There is also sufficient heating of the day with temps in mid 90s along much of SE Florida due to a lack of seabreeze development in advance of the cold front.

It would appear though that most of Broward and Miami-Dade will not receive rainfall from these storms as they are racing off to the ENE and offshore into the Gulf Stream.

000
FXUS62 KMFL 111831
AFDMFL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MIAMI FL
231 PM EDT SUN MAY 11 2008

.SHORT TERM...TONIGHT THROUGH MONDAY NIGHT...SHORT WAVE JUST SOUTH
OF THE GREAT LAKES WITH ASSOCIATED COLD FNT ACROSS SE U.S. WILL
CONT TO PUSH EAST THROUGH THIS PERIOD. MOST ENERGY WITH THIS SHORT
WAVE WILL BE TRANSFERED NE AND WELL NORTH OF THE AREA. THIS WILL
RESULT IN NOT SO GOOD UPPER LVL DYNAMICS AS THE FRONT MOVES TROUGH
THE LOCAL AREA AND SO THE MOST WE CAN EXPECT IS JUST ISOLD
SHWRS/MAYBE A TSTM. FROPA SEEMS MOST LIKELY MON NIGHT WITH A DRIER
TREND STARTING AFTER THAT. STILL ABOVE SEASONAL AFTERNOON TEMPS
MAY BE EXPERIENCE AGAIN MONDAY AFTERNOON DUE TO THE WARM SW FLOW
BEFORE FRNT GETS HERE.

[gatorcane]

Sanibel, you can be "statistically" overdue based on previous climatological return periods (as you mentioned), but the chances for a hit never increase or decrease. This has been repeatedly hashed out in many threads.

I'm sorry, but since the dry May theory relies on science, it should be subject to the same scientific scrutiny.

MiamiensisWx, I agree the theory is controversial and we just don't have enough data to really draw any absolute conclusions. Indeed most of South Florida's hits come from the Caribbean and NOT the Atlantic as many would think. The dry May theory certainly is suggesting that the presence of a strong sub-tropical ridge would persist as a long-wave pattern through the summer months, which we know is not entirely true. For example, 2004 is a good year that shows that even if the early part of the summer months feature EC troughiness, that the prime August-October months may coexist with a long-wave pattern marked by a strong sub-tropical ridge in the Western Atlantic. It would be interesting to monitor May rainfall and see what happens this year though.

[gatorcane]

Rainfall update, May 12:

Some rain has fallen but not much. Extended forecast is extremely dry as ridging builds across Florida again after an unseasonably strong cold front pushes southward tonight and fizzles over extreme Southern Florida and the Florida straits.

Miami International: MONTH TO DATE 0.05
Ft. Lauderdale International: MONTH TO DATE 0.02
West Palm Beach International: MONTH TO DATE 0.24

[JonathanBelles]

Completely dry up here:
TPA, Lakeland, PIE, Sarasota, Punta Gorda, Fort Myers, and Ruskin all report zip for the last 11 days with traces in a few spots for today.

[Blown Away]

The SFL rainy season generally begins mid May, but it has been very dry so far!

[Decomdoug]

Port St. Lucie is dryer than popcorn. We had a teaser shower last week that was about twenty drops on the hood of my truck. Just enough to water mark the new wax job. Wind is about 30mph here from the S.W. so if things wern't already dried out they will be now.

[Nimbus]

The driest May on record for south Florida was in 1965 when they only got .6 ", that was the year hurricane Betsy came through the northern keys as a Cat 3. The second driest May for south Florida came in 1992 with a rain total of .9" for the month and yes that was the year Andrew blew through as a Cat 4/5. The third driest May on record for south Florida was in 1935 and that year the Labor day hurricane hit the keys, it was the strongest hurricane ever to hit the US coast.

Statistically the last part of May is rainier in south Florida, lets hope the statistics hold true for that this year.

[MiamiensisWx]

The most disconcerting aspect of an abnormally dry May will not be the threat of tropical cyclone landfalls; the real "threat" is manifesting itself in my parched lawn and the Volusia/Brevard County brush fires.

[Blown Away]

The driest May on record for south Florida was in 1965 when they only got .6 ", that was the year hurricane Betsy came through the northern keys as a Cat 3. The second driest May for south Florida came in 1992 with a rain total of .9" for the month and yes that was the year Andrew blew through as a Cat 4/5. The third driest May on record for south Florida was in 1935 and that year the Labor day hurricane hit the keys, it was the strongest hurricane ever to hit the US coast.

Statistically the last part of May is rainier in south Florida, lets hope the statistics hold true for that this year.

There may not be concrete scientific data to support the dry May theory, IMO it is not a coincedence those storms struck SFL during those dry years. The top three dry May years resulted in three legendary SFL hurricanes.

[Nimbus]

Its kind of odd that each of the three major hurricanes that formed after the three driest Mays were only the first or second storm of their seasons. The Labor day hurricane was only the second storm to form in 1935.

I read that there were over 3000 acres currently burning in south Florida. Thats a lot more than the end of the dry season fires you usually get isn't it?

[Sanibel]

Had a 3 minute shower this am and the front dried up shortly after.


Low humidity and unusually cool and dry for season today.

Still dry.

[Blown Away]

The average SFL May rainfall is near 5.5". The top 3 driest SFL May's are: (1965 - .6" = Betsy)(1992 - .9" = Andrew)(1935 = Labor Day Hurricane). I'm going to set the benchmark for the Lushine dry SFL May theory at 1", since their has not been a clear definition for what is considered a "Very dry SFL May". I'm going to be watching the SFL rainfall gauge closely this month.

[gatorcane]

Absolutely no rain in sight and near record highs are possible this weekend again over Southeast and eastern portions of Florida. The expected dominant SW windflow will prevent any SE seabreeze to develop. NWS mentions the rain chances are much below normal for this time of year.

Touring the Palm Beach and Broward county roadways, its is BONE dry here -- the driest I have seen here in quite sometime. Many grassy areas along the interstates and highways look completely "torched."

Sun-sentinel article on fires in Eastern Florida:
http://www.sun-sentinel.com/news/local/ ... 9419.story

NWS Miami snippet:

IN THE EXTENDED FORECAST...GLOBAL MODELS CONTINUE TO SUGGEST THAT
NORTHERN EXTENT OF A LARGE SUBTROPICAL RIDGE WILL REMAIN IN
PLACE OVER SOUTH FLORIDA THROUGH THE END OF THE WEEK...AS A REX
BLOCK BECOMES ESTABLISHED ACROSS THE WESTERN HALF OF NORTH
AMERICA. ALL AVAILABLE GUIDANCE ALSO SUGGESTS THAT AN UNSEASONABLY
DEEP UPPER LOW WILL DEVELOP OVER THE GREAT LAKES REGION THIS
WEEKEND...WITH THIS FEATURE LIKELY PERSISTING INTO THE FIRST PART
OF NEXT WEEK. THIS PATTERN WILL FAVOR DEEP-LAYER SOUTHWEST FLOW
DEVELOPING ONCE AGAIN ACROSS SOUTH FLORIDA...WITH THE POTENTIAL
FOR ANOTHER EPISODE OF VERY WARM TEMPERATURES...SIMILAR TO WHAT
WAS EXPERIENCED OVER THE LAST COUPLE OF DAYS. ALTHOUGH A WEAK
FRONTAL BOUNDARY MAY TRY TO PENETRATE THE AREA SOMETIME EARLY IN
THE WEEKEND...RAIN CHANCES WILL REMAIN VERY LOW FOR THIS TIME OF
YEAR.

[Sanibel]

We had a drought last summer, so chances are we'll see some convection rain form towards the end of the month. Don't count on a dry month just because the first half is dry.

[fci]

I think there is a very rational explanation for predictions of an active tropical season when it is very dry in May.

The law of averages.

Ultimately, South Florida will have to make up for the lack of rain in May (and June if the pattern continues).
How is this defecit get made up?

By copious amounts of rainfall coming some other time during the year.

We just won't stay dry all season,
That would be highly, highly, unlikely.

So, the easiest way to get copious amounts of rainfall to counter-balance the lack of early season rainfall is through tropical activity.

Could be a series of TD's or Tropical Waves or a big storm or two to drop 20 inches or more on us.

Either way, the rain will get here.
By a change in the pattern to bring up the rain guage or a couple of rain laden tropical systems during the season.

Mother Nature (not particularly scientific I must admit) finds a way of balancing things out.

[gatorcane]

Latest NWS Miami extended outlook. Could May 21st (Wed) be the official start of the rainy season?
If these models hold, the rainy season would be right on time.......

MEDIUM RANGE GUIDANCE FROM THE GFS/ECMWF INDICATES THAT THE
PATTERN OF LOW-LEVEL SOUTHWEST FLOW...WARMEST AFTERNOON
TEMPERATURES ALONG THE ATLANTIC COAST...AND SLIGHT CHANCES FOR
SHOWERS/STORMS ACROSS THE NORTH WILL CONTINUE ON SUNDAY/MONDAY...
AS A REX BLOCK IS FORECAST TO REMAIN SITUATED ALONG THE WEST COAST
OF THE CONUS. HOWEVER...THIS PATTERN IS FORECAST TO EVENTUALLY
BREAK DOWN AS A STRONGER UPSTREAM TROUGH APPROACHES THE PACIFIC
NORTHWEST AND DEEP UPPER LOW OVER THE NORTHEAST/GREAT LAKES REGION
BEGINS TO LIFT NORTHEASTWARD. THIS WILL PLACE SOUTH FLORIDA BACK
IN WEAK SOUTH FLOW FOR THE MIDDLE/LATTER PORTIONS OF NEXT WEEK...
WITH SLIGHTLY COOLER TEMPERATURES AND IMPROVING RAIN CHANCES
BEGINNING ON WEDNESDAY.

[Sanibel]

Chilly and windy last night at 63*

The heat blanket is a week late.