Water Log 8/26

Wet season enters final phase, dry conditions prevail
Week of August 20-26

We have a few days left in August. Surprisingly (how time flies), that puts us about three-quarters of the way through the core part of the 4-month summer rainy season. September — with a 10-year 8.1 inch average — is our last core month of the rainy season. Bountiful rains can also fall in October, but with only a 3.5 inch 10-year average, it tends to be more or less a hit or miss month depending on twists and turns of storm tracks blossomming out of the tropics.

District-wide, June, July, and August rainfall tally has been slighlty below average, tallying about 10 percent less rain than the 10-yr 23.5 inch average 3-month total. We still have a few days in August left, so the outlook may change, but August is shaping up to be a dry month.

Less than 5 inches of rain has fallen District-wide since the start of August. That’s 40 percent less than 7.8 inch 10-year August average. Miami-Dade has been particularly dry. Its only received 3 inches of August rain to date. That’s a stark contrast to its bumper crop of the 13 inches it received in June. Water Conservation Area 3, East Broward, Lake Okeechobee, the Lower Kissimmee, and East Caloosahatchee Basins have also received under 4 inches of August rainfall to date.

The Southwest Coast and East Palm Beach have seen the rainiest August — both with just above 6 inches of August rain to date — but even that is dry by typical August standards. Four gages in southwest Florida — Gum Slough and Monument Road in Big Cypress NP, Southern Golden Gate Estates along I75, S78 along the Caloosahatchee have received a relative whopping +30 inches of rain over the past 90 days, but many of southwest Florida’s more coastal stations (between Naples to Ft Myers) have received less than 15 inches over the same period.

Up North the start of September is associated with arrival of Fall cooling. Daytime highs and nightime lows have dropped into the high 70s and low 60s, respectively, in Baltimore and Boston. But Florida daytime highs and nighttime lows are still hovering steady in the mid 90s and mid 70s, respectively. Daytime highs in Naples typically stay in the 90s through most of September, with nighttime lows not dropping back below 70 until the first part of October. That occurrence typically coincides with official declaration of the wet season’s end.

For the record, this August has been especially hot across Florida — most likely caused by the relative lack of August rain. Daytime high temperatures rose above 95 degrees over a half dozen times in Naples, and daytime highs in Tallahassee stayed above 95 for most of the month. Even daytime highs in Miami have been running a few degrees above the 90 degree average.

Around 500 cfs continues to flow into Lake Okeechobee from the Kissimmee River. That’s about half the inflow rate of the beginning of August when flows returned to the Kissimmee after an 8-month hiatus. The Lake remains at its lowest August level on record. You have to go all the way back to August of 1981 to find an August lake stage of below 10 ft mean sea level (Interestingly, Lake stage jumped up to 11 ft msl by the end of August 1981). Currently Lake stage is around 9.5 ft msl. That’s about 2.5 ft below late August of last year, and 5 ft below the late August average over the past 5 years.

Regulatory stage in Water Conservation Areas 1 and 2 are tracking right around average levels for late August, and tracking just about the same elevation as late August of last year. Slough water depths in central Loxahatchee are around 1 ft deep, placing the wetting front at or above the ridge landscape type and inching into the bayhead zone. Currently over 3.5 ft of water is pooling behind the S10 and S11 structures, both of which remain closed (and have been closed for the entire wet season to date). Slough water depths just upstream of the S11s are currently around 2.75 ft deep due to water impounding behind levee.

Regulatory stage in Water Conservation Area 3 is currently around 9.2 ft msl, which is 1.6 ft below the 5-yr late August average. That places it at a 17-yr August low-water mark. Keep in mind that prior to 1990, water levels in 3A similar to what we are seeing this August were a more common-place occurrence. August stage in 3A dropped below 9 ft msl in 1965, 71, 77, 81, 87, 89, and 90. Much wetter conditions have prevailed in 3A since 1990, and even this year’s 9.2 ft msl stage level is a notch above the periodic sub-9 ft Augusts of the 60s, 70s, and 80s.

This is shaping up to be the year of no flows to Everglades National Park — at least through the S12s. Last year S12 flows didn’t ramp above 1000 cfs until the middle part of September, so there’s still time. But keep in mind that last year’s regulatory stage in 3A was around a foot higher than our current condition, and rose to over 11 ft msl by the end of September. In both 1989 and 1990, summer discharges through the S12s were short-lived (around a month or less), and never exceeded 500 cfs. This year is shaping up along those lines, if not less, unless meteorologic conditions turn for the wetter in the next 6 weeks. Freshwater input into the Park at Taylor Slough headwaters (through the S332s) has dropped down since the start of August, presumably as a result of low rainfall levels in the C111 basin and headwater flows from the north (S334 and S335). Over the past 5 years, the S332s have averaged around 500 cfs August discharge rate into the Park. Headwater flows into the Park from Big Cypress National Preserve and Northeast Shark River Slough are also down. That makes Everglades National Park pretty much a rain-driven watershed this year!

Over in Big Cypress National Preserve, wetland stage is tracking just an inch or two below the late August average, which incidently coincides with the same level we were at late August of last year. Preserve-wide stage has risen up into the base of our hydric pinelands. The wetting front reaches that height for about a 3-month span, from early August to late October during the typical year. The southern half of the preserve south of US41 remains wetter than I75. Flows measured across US41 are at a 5-yr August low, flowing at less than 500 cfs in comparison to a 2000 cfs 5-yr late August average.

Summer rains continue to largely miss Corkscrew Swamp Sanctuary. Water levels are tracking at a 17-yr August low. You have to go all the way back to August 1990 and before that to August 1970 to find similarly low water levels at the Sanctuary. Late August of last year the wetting front had risen above the cypress and wet prairie habitat into the hydric pines. So far this summer water levels have yet to even rise out of the lowest of low-water refugia along the boardwalk. The swamp forest habitat has been dry for 6 months consecutive months (since early march), and wet prairie habitat has been dry for 10 consecutive months (since late October).

Suffice it to say it’s been a dry August in South Florida, and is shaping up to be a lower than normal wet season unless we get a strong 1-2 punch from September and October.

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