May 6, 2015

Hot and humid season (in view)

Memorial Day coincides ...

With the traditional start of the rainy season.

The graph above shows daily high and low air temperatures measured at Naples Airport compared to the long-term average and historical extremes.

Can you see it also occurs when long-term nighttime low temperatures rise (and stay) above 70° F? Meteorologist usually use that, not Memorial Day, as the more scientific guide. Notice, too, the hotter than normal temperatures for April. That explains why the buildup of afternoon rains during that span.

Also explains why I enjoyed that cool respite in early May so much.

Once June starts those days are through.

May 5, 2015

May 4, 2015

Return to "normal" drought

Swamp levels rose over a foot ...

Thanks to last week's big rain storm.

This hydrograph shows the rise and fall of the water table in Big Cypress Nat'l Preserve over the past two years.  The blue line indicates the past two years.  The dotted white line indicates the long term average.  The horizontal changes in color coding show the elevation of the major habitat types in the swamp.

That puts us right at the long-term average for early May.

But we're not out of drought season yet.

The water table doesn't usually bottom out until mid May.

May 3, 2015

Turner River Headwater Culverts

These culverts feed water from Turner River Canal to Turner River several hundred feet downstream

May 1, 2015

Turner River Headwater Plug

Here's a short video on the upstream
source of the Turner River

Apr 30, 2015

New water year begins!

Most people think the new year starts in January,

But for south Florida hydrology the water year starts fresh May 1st.

Effective May 1st, 
the new water year
has begun

Compare that to continental hydrologists who universally ring in the new water year each October.

October is the northern standard because it coincides with the annual ebb of the water table. Fall approximates the inflection point when the steadily dropping summer water table bottoms out and slowly, and sometimes fast, starts to rise ... usually peaking in spring.

South Florida's water cycle is reversed:

Water levels rise (not fall) all summer long, finally peaking in fall during the summer rainy season's end, then followed by the long steady drop of the winter dry season water table which, in its final days of spring, accelerates at a drought defying rate.

Both low-water times
of the year for each area

We still have some dry days ahead of us in May,

But for accounting purposes, the new year has begun.

And thanks to the timely rain this year's threatening deep drought appears about done (as shown below).

Six month season draws to close

With one day to go ...

Here's the swamp's April and Dry Season rain totals.

This table provides a history of monthly, wet/dry season and yearly rainfall from 1989 to present.  Warm colors indicated lower rainfall months and cool colors indicate higher rainfall months.  Can you see the blockbuster rainfall numbers the swamp got in June 2005 and for the year in 1995?

April 30th marks the end of the six-month dry season that began on November 1st.  Thanks our last minute rainstorm, a wetter than normal April (3.9 inches compared to 2.6 inch average) our dry season total pushed this year's dry season total (i.e. going by those six months) to the normal range (11.1 inches compared to 11.3 inch average).  That rain event also ended the seasonal spring drought.

Not that the dry season is over.

We can expect more dry weather into May ...

Until closer to Memorial Day when the summer rainy season starts cranking into full gear.

Apr 29, 2015

Second Big Rain Day Strikes!

Yesterday's rain qualified as an ...

Official Big Rain Day (BRD)!

This calendar chart reports south-Florida-wide daily rainfall from 1992 to present.  Daily rainfall amounts are aggregated into three categories: Little to no rain days, a moderate dose of regional rain day, and Big Rain Days.  Our most recent rain day is our second of this calendar year.  Last calendar year we only received two.

What is a BRD?

It's any day when on average one inch of rain (or more) falls across all of south Florida.  Big Cypress National Preserve averaged 1.77 inches of rain and the Miami Dade Basin averaged 2.6 inches. Interestingly, BRDs occur throughout the year, not just the summer rainy season.  The source of the winter and spring are usually continental fronts.

South Florida typically gets about 4-5 BRDs per year.

Yesterday's was perfectly timed to end the seasonal spring drought.

All's well that ends well

Here's a sneak peek ...

At last night's rain totals.

Colors indicate rain intensity
as estimated from radar imagery

Not to be confused with the wet season's start.

The cooler air moving in for the weekend makes this the dry season's farewell storm.

Talk about ending on a strong note!

Apr 28, 2015

Apr 27, 2015

Seasonal anatomy of drought

Drought in July?

Not in the Big Cypress Swamp.

The above chart shows the monthly distribution of moderate and severe drought in Big Cypress Nat'l Preserve as calculated from 1992 to present.  Moderate drought occurs in the four-month span from February through June. Severe drought only occurs in three months -- April, May and June. That leaves the other seven months -- July through January -- as being virtually drought free. Interestingly, June is our rainiest month but also a high drought month, too. The reason for that is that during deep drought years the severe draw down of the water table by late spring requires time to fill back up. Also factoring in are those years when the wet season is late to start or we have an especially dry May.    

The chart above proves it.

Summer rains by then are guaranteed to have filled up the shallow aquifer and flowed over into the surrounding low lying swamp.   But don't count drought in June out even though traditionally it is our rainiest month.

That's why I often call June soaking in season.

And that's why this year's drought season could still have a ways to go.