Miami’s October rains

October rains drench Miami. That’s not all too unusual.
Week of October 22 – 28

RAINFALL

Stalled fronts are an underappreciated rainmaker in south Florida, especially when you throw in a sea breeze and the prevailing easterly trades. That combination has made for a wet October over on Florida’s southeast coast. (SFL-wide rainfall)

Miami-Dade county is just a notch below 10 inches for the month, and East Palm Beach and East Broward are both above 8 inches for October.


Recent photos of Moore Haven S-77 navigational lock and dam. Its the Source of the Caloosahatchee, connecting the river to the Lake, and part of the Okeechobee Waterway.

Over on the other coast — spanning an area from Naples to Ft Myers — under 3 inches of rain has fallen over the same period. Lake Okeechobee and the East Caloosahatchee Basin are also under 3 inches.

Over the past 365 days, that puts Miami-Dade at 64 inches of rain. That’s more than twice the amount that’s fallen over the Lake (31 inches) in the same period and over 20 inches more than Naples and Ft Myers’ area (41 inches).

The backstory to these numbers is that October rains are typically more plentiful in Florida’s lower east coast than the interior and southwestern parts of the pensinsula. Miami-Dade has averaged 5.4 inches of October rain over the past 10 years. The Naples-Ft Myers area October average is only 2.9 inches.

In fact, other than October 2005 when Wilma hit — ending October 2005 with almost 10 inches of rain — you have to go all the way back in time to 1996 to find the next October when Naples-Ft Myers area recorded in excess of 5 inches of October rain. Five inches is Miami’s October average. Miami-Dade has had October rains in excess of 9 inches six times since 1995: 1995 (10 in), 1996 (8 in), 1999 (12 in), 2000 (12 in), 2001 (9 in), and — after a 5-year lull — again this year (~10 in).

Therefore, and interestingly, its not that the southwest coast and the Lake haven’t received their fair shares of the October rain clouds — they are actually both tracking average for the month — it’s that the lower east coast has received twice its normal October amount, which is a higher October rainfall average to begin with.

Peaking back in the history books, South Florida’s rainiest October in recent memory was the El Nino influenced October of 1995. Over 10 inches of October rain fell District-wide and a whopping 17 inches drenched the Naples/Ft-Myers area. That was one October where Naples pulled a surprise upset over Miami, which only recorded 10 inches for the month.

FLOWS

Last week we made use of Fenway Park to make a historic discharge comparison for the Caloosahatchee at the WP Franklin S79 dam. That was lucky timing — considering the 4 game sweep offered under a week window. That’s the third world series sweep in 3 years. Its was good to see some of the old Florida Marlin’s ballplayers from the 2003 World Series Team make good — both Josh Beckett and Mike Lowell — even if its for another team. Players must ultimately be judged by their contributions on the field and in the club house. Give me a player with a few good intangibles anyday over pure statistics, whether it be clutch hitting or shut-down pitching. The Sox front office has perfectly balanced a number-rich grasp of sabermetrics with clubhouse chemistry. That’s a perfect brew. To Red Sox fans everywhere — congratulations!

But back to hydrology.

Over 3 million acre-feet discharged out of the Caloosahatchee’s S79 WP Franklin dam in 2005 and 1995. That rate would fill Fenway’s fenced in 3 acres of turf with a 183 story high skyscaper per day. About 100 of those stories would be filled with Lake Okeechobee releases from the upstream S77 Moore Haven Dam. The rest of the 183 story building — think a giant glass — would be topped off with water from the Caloosahatchee watershed, not the Lake.

The graph below provides a comparison of the Caloosahatchee River’s annual flow volumes in recent years as derived from the Lake Okeechobee versus drainage from the Caloosahatchee watershed.


The Lake water proportion of S79 discharges saw an increase in the middle 1990s, presumable in response to increased rainfall and Lake stage. Compare that to the mid 1980s and early 1990s when contributions from the Lake only filled Fenway with 6 stories of water, similar to the low discharge levels we’re seeing this year in 2007.

Since 1970 the highest discharge rates through the S77 occurred during the Spring of 1983 and 1998 — both El Nino years — and not during the late Summer or Fall as you’d expect, since its late Summer and Fall — not Spring — that corresponds to south Florida’s traditional peak of the water cycle.

WATERSHEDS

Lake Okeechobee covers 730 square mile area with an average depth — during a normal year — of 9 ft. That computes to an approximate volume of 4 million acre feet. Compare that to Lake Lanier — Atlanta’s drought-stricken water source — that covers a spidery 59 square mile area, but at an average 160 ft depth stores around 6 million acre-feet of water. That’s a back-of-the-envelope calculation.

They are currently releasing around 3 billion gallons of water per day from Lake Lanier’s Buford Dam to maintain minimum flow levels into Florida’s downstream Appalachicola Bay. That computes to a 4,600 cfs flow rate. In comparison, the S79’s 3-yr average flow rate between the peak discharge years of 2003 and 2005 was just under 4,000 cfs. That means that Buford Dam’s minimum flow rate — extrapolated over a 3-year period — would equal the same volume associated with WP Franklin’s peak discharge years. That speaks volumes of how little storage we have in south Florida’s flat landscape, and how little wiggle room there is for error.

Lake Okeechobee stage has risen 8 inches since mid September. That’s good news considering Lake stage fell the same height during a similar 7 week period last year. This year’s presence of October rains — on both the Lake and the Kissimmee — has made a difference.

Loxahatchee remains perched above 17 ft mean sea level. That’s 7 ft higher than the surface of the Lake. That’s also a half foot higher than Loxahatchee’s 5-year late October average, and also about a half foot higher than late October of last year. Central slough water depths at Site 1-9 are around 2.5 ft deep. That’s the deepest its been there since October 1999.

Incidently, that puts Loxahatchee at a new 5-year high water mark and nearby Lake Okeechobee — just 25 miles away as the crow flies — at an all time October low.

The S11s are discharging around 1,000 cfs into downstream Water Conservation Area 3. That and rainfall has boosted regulatory stage in 3A to above 10 ft mean sea level for the first time in over 10 months (since early November of 2006). That’s brings 3A’s regulatory stage just 2.5 inches below the surface of Lake O. Slough water depths in southern 3A are also around 2.5 ft deep, just like up at Loxahatchee.

Around 400 cfs are discharging into the Park from the S12s, with an another approximate 500 cfs discharging into the Park east of the S12s through The L29 Culverts. Despite all the rain in Miami, those showers have not extended far from the coast. Shark River Slough depths remain at a 17-year October low. You have to go all the way back in time to 1989 and 1990 when October water depths at the Park’s P33 hydrologic monitoring station were under a foot deep, in comparison to this year’s 1.3 ft depth, and in comparison to a 2.5 ft depth in October 2005.

Big Cypress National Preserve swung and missed on its early Fall swing for the pine flatwood fences. What I mean by that is that this Summer the preserve’s wetting front, as a whole, never extended up into its traditional high-water mark territory — the pine flatwoods. Water flooded the swamp forest, cypress, and wet prairie habitats, but only skirted around the edges of the higher pine country. You often hear the term pine islands in south Florida, and that’s the reason why. They are islands of pine in a vast sea of shallowly flooded wetlands.

Despite never quite reaching its traditional Fall apogee, the modest dose of October rains — around 4 inches so far — has been enough to sustain the preserve’s wetting front at the same height its been at since late August. Preserve-wide stage is currently at the same height as the 5-year late October average, and also at the same height of late October of last year.

The preserve has straddle the fences between the drought (Naples) and drench (Miami) that has played out this Wet Season on opposing coasts. This time next week it will officially be November — the page on the calendar that marks the first page of the 6-month Dry Season and the last page of the last page of the 6-month Tropical Storm Season.

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