All eyes on 70

Rain Or Shine Report for May 14
May hits midpoint dry and rainless
A closer look at 70, 1998, 430, 3, and 8-10


70º F is a milestone temperature in south Florida.

During the winter, it means that a cold front has passed through.

Whenever daytime highs stay below 70º F, especially for a couple days in a row: that’s a meteorologic event that has us all throwing on sweaters.

Admittedly, that’s only cold by south Florida standards, … but still, it’s the metric we use to tell ourselves “brrrr” its cold out there, and yes, there’s a place in south Florida for sweaters other than for staying warm “indoors” from the cool blast of the air conditioning, also usually set at 70º F (or so it seems).

During the summer, or leading up to the summer, that same 70º F is a trigger for tripping the switch on the summer rain machine.

The rule of thumb is that the summer rain machine starts revving its engines in earnest when night-time lows consistently stay above 70º F.

Other meteorologic principles also come into play. A dome of high pressure has been known to descend over the peninsula, pushing down from above, and stifling cloud formation that typically takes place when the 70º F barrier is broken.

That’s what has been happening here recently.

It’s been hot, and nighttime lows in Naples have risen above 70º F, but still no showers.

But fear not: when it rains it pours in south Florida – and that should start happening as May grows a little longer in the tooth, or by early June at the latest.


The Lake is 8 feet lower than May of 1998, but the spurt of winter rains in February, March, and April had us scrambling in our historic notes with comparison of this winter to the El Nino wetted winter of 1998.

Water levels in Big Cypress National Preserve never quite reached 1998 winter levels, but it did up in Loxahatchee, where water levels are only now dropping out of 5-year high level territory they’ve been treading for past couple months.

To be sure, this winter was not a hydrologic match to winter of 1998, but now I’m reading in the papers that the heart of the drydown is becoming comparable to 1998 in terms of wildfire severity. That was the year that Florida wildfires made National news in a big way.

This year’s winter rains have fueled the springtime bloom, and now, with the recent change of weather to the drier – including hotter-than-normal temperatures and some strong winds – is parching the landscape into a tinderbox, reminiscent of 1998. We’ve seen that in the Lake – where around 5,000 acres have burned – and north of the Lake in central Florida.

Keetch Byram Drought Index (KBDI)

Source: Florida Division of Forestry

That’s ironic, because so often we think of water as extinguishing fire, which it will once the summer rains kick up – but in this case, the winter wetness laid the groundwork for the current wildfire severity.

South Florida is pretty amazing that way – it always tests one’s assumptions, and demands close vigilance to the history books.
Location of water table in Big Cypress National Preserve, relative to last year, the average, and 1998.


Lake Okeechobee is approaching its 430th day below the 11 ft mark.

And earlier this week also dropped back below 10 ft (see Sun Sentinel story). That’s a significant milestone because below 10 ft is even with the deeper marsh potholes within the littoral march go dry.

Looking back to the drought of 2001, Lake stage only dropped below 11 ft for around 200 days, or 7-8 months. The current streak below 11 ft is in its 15th month.

Will we see relief in May?

The Southwest Coast basin – an area that includes Naples and Ft Myers – has averaged 3 inches of rain in May over the past 10 years. That’s similar to the May average for the Lake and the Kissimmee. The biggest May rainfall total over past 10 years was when 6 inches fell in 2003.

Miami-Dade has averaged 5 inches of rain over the last 10 years, and recorded almost 8 inches in May 2003.

Most of the other basins south of the Lake average 4 inches of rain in May.

May is hit or miss, but count on the summer rain machine to kick in by June, and for it to deliver on the first of 4 consecutive months of 8-10 inches of rain.

October – May’s twin counterpart as a shoulder season month to the summer wet season – is also hit or miss: but the misses are sighs of relief because the hits are our fabled and feared tropical systems.

But they are not always the high-energy hurricanes that deliver the big rains. Poorly organized tropical systems can be the real rain makers in terms of filling up our watersheds for the dry season to follow.

But first thing first.

Let’s see when the dry season officially ends, and how much rain we get out of the gate in June. Will it be a June 2005 – when +20 inches fell across the region – or will it be a June 2006 or 2007 when under 7 inches fell in June across the southern peninsula.

Only time will tell.

In the meanwhile, my guess is that the Lake will easily make it to 450 days below 11 ft.

Another view of Upper Wagonwheel Road (right), where it intersects with Birdon Road (left), looking west into Deep Lake Strand.

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