Rainfall

Bar chart dynamics
How to read a monthly rain chart

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South Florida has two distinct meteorologic seasons:

A 6-month wet season and a 6-month dry season.

How to read a rain chart

Things you should know: (1) The water year begins anew the start of May each year. But it’s not an exact science (i.e. precise point) when they start and end from one year to the next. For example, we classify October as a wet season month even though the afternoon rain showers usually end in early October. And the start of May is probably the swamp’s driest time, yet it’s also the same month, as it approaches June, that the summer rainfall pattern begins. (2) Most of my rainfall charts show background gray coding. That’s the historical statistics as counted from 1983 to present. Why 1983? It was a good year, and most of the SFWMD’s record by basin reaches back that far. Looking at the chart above, the dark gray band is the average range for each month (i.e. between the 25th and 75th %tile) and the light gray is the historic rang (i.e. between the max and min). The white bar in the middle is the normal or median monthly rain. (3) My charts are based on basin-wide rainfall, not local rainfall.

Newspapers calculated rainfall by calendar year. (They are wrong. How dare them!) They also calculate rainfall for an individual gage in Ft. Myers and Naples (The shame!).

In summary, numbers mean more if you can frame them against the expected values and ranges that came before. And its by water year, not calendar year, that we tally rainfall totals in south Florida.

rain charts

Rain Table and Map
Swamp-wide view

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No, water does not flow up hill.

But trying to keep up with it often feels like an uphill battle.

Table of monthly rainfall

My solution: No one graph, table or map usually tells the full story. You need a combination. And even then you usually have to be looking out the window, too. But looking out your window can be deceiving, too.

That’s where aggregating data by watersheds or basins comes in handy.

Rain for the past 7, 30 and 90 days (in inches)

History of Junes
First month of wet season ends strong

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This June didn’t register on the epic scale …

Of over 20 inches falling, (i.e. 2005 or 2017).

Calendar chart of monthly rain in the swamp

But after a slow start,

It eked it’s way into the long-term normal range …

Making it the rainiest month since September of 2020.

Monthly rainfall in the Big Cypress

The swamp still has a lot of filling up to do …

But over 8 inches for June is a solid start.

Afternoon storm bearing down, looking east down Wagon Wheel Road

That being said, some domes are still completely dry.

big weather

Rain mechanic (at work)
Parts on order

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The good news is …

We finally figured out the problem.

As seen at John Stretch Park

The only catch is …

It could take a week or two for the part to come in. In a nutshell, there’s a high pressure system forming over the southeast United States. That will pump dry air into Florida into next week.

Zen and the art of rain machine maintenance

After that, around Memorial Day, expect the rain machine to start cranking up.

Rain machine mechanic
How to kick start a rain storm

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There’s no secret to …

What it takes to crank up Florida’s rain machine?

South Florida’s rain machine

All good rain mechanics know you have to get nighttime lows to stay above the 70° F line.

That’s when the good humidity really kicks in.

Daily high and low temperatures for Naples Florida

Looks like we’ll be crossing that line this week.

Go rain machine go!

As seen at John Stretch Park

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Big Cypress Rainfall Record

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The numbers are (almost) in for Water Year 2021:

The Big Cypress received 43 inches of wet season rain and 14 inches of dry season rain, or a 75/25 percent split between the two seasons, for a grand water year total of 57 inches of rain.

History of wet (blue) and dry (orange) seasons rains for the Big Cypress Watershed

Despite the more bountiful summer rains, it was the dry season rains (and specifically November, and even more specifically one storm – Eta) that put the Big Cypress in the “above normal” range for Water Year 2021.

As you can see in the chart below, even the “above average” dry season had a significant rainless spell from January through March (i.e. the red slashes). And who’s to say we’re out of the dry season yet:

A dry May could yet drop the swamp to deep drought

The same data as above, shown monthly in the form of a calendar chart

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Dry season wrap up?
And why it's not over yet

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The dry season isn’t over …

But it’s entering its final weeks.

Rainfall over the past 7, 30 and 90 days across south Florida

When does the rainy season start?

Afternoon showers can start sputtering in April and early May, but it isn’t until later in May and early June that the water table typically rebounds.

Whatever the case, the verdict is in:

The 6-month dry season was was wetter than average across the entire southern peninsula with the exception of the Upper Kissimmee and with the lower east coast leading the way. District-wide, south Florida averages around 13 inches of rain compared to the 15 inches recorded this year.

Basin by basin comparison rainfall since the start of the dry season (blue) and the start of the calendar year (red). The hollow black bar shows the dry season average.

But May is a pivotal rain month.

Typically drought extends and deepens in its early half before the afternoon showers kick in or we get a big regional storm.

One more week, and Water Year 2022 is here!

As usual, it’s a wait and see.

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Statewide rain
The case for more than one rain gage

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What if all the raindrops were spread evenly …

Across the entire state?

water clock

Animated rain comparison between all of Florida and just south Florida

Actually, it sort of is:

Every part of Florida averages plus or minus 50 inches of rain.

But there are regional differences, too.

South Florida gets the least amount of winter rain whereas the panhandle gets the biggest dose of springtime fronts. That gives the Suwannee District a bump of rain at the same time when south Florida is descending into its deepest drought. As for the driest time in all of Florida: The month is May. And the wettest? September is Florida’s typical highwater month.

Take home point:

As useful as a statewide average is, we highly recommend more than one rain gage.