I know that summer in the northern hemisphere begins on the longest day of the year. Summer here in Central Florida, as far as I am concerned, begins when the low temperature for the day is 75 degF (24 C for those of you outside of the US). We hit that point this past week. Our morning low was 74.9 degF, and the dewpoint was right at the same temperature. The high was 92 degF (33 degC) today.

The reason for this, is that the low temperature can’t go any lower than the dew point. At that point, any further energy lost from the atmosphere is spent condensing water vapor, not reducing the temperature. When the dewpoint is at that point, the air starts becoming thick and the afternoon rains begin. If you have ever been in Central Florida during the summer, you know that it rains virtually every afternoon. That’s where we are now. Summer is here.

The dew point temperature is the temperature at which the air can no longer hold all of its water vapor, and some of the water vapor must condense into liquid water. At 100% relative humidity, the dew point temperature and the air temperature are the same, and clouds or fog can begin to form. While relative humidity is a relative measure of how humid it is, the dew point temperature is an absolute measure of how much water vapor is in the air (how humid it is). In very warm, humid conditions, the dew point temperature can reach 75 to 77 degrees F, but rarely exceeds 80 degrees.

Dew point is the best indicator of comfort in a hot climate. Once the dew point of the air exceeds 66 degrees Fahrenheit or so, the air begins to feel hot and uncomfortably stuffy. The reason for this is that your perspiration can not evaporate to cool you off.

The dewpoint here will slowly increase from now until summer breaks in late September. The people who live here know that anything needing to be done outside between May and September is best done before 11 am, when the thermometer typically breaks 90 degF. It isn’t the temperature, it’s the dew point.

Here in Florida, there are 4 seasons:

Hot: March through May
F’ing Hot (Also known as Hurricane season): June through mid September
Still Hot: Mid September through Mid November
Snow Bird: Mid November through February

Beginning in mid June, you get your outside work done in the morning then stay in the air conditioning until at least 4:30 in the afternoon when the afternoon thunderstorms come calling. That is what we do from mid June until about the middle of September.

 

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11 Comments

Don W Curton · May 15, 2024 at 7:09 am

For a few years I moved from South Texas (near the coast) to West-by-God-Virginia. It was work related. In any event, during the summers it’d get up to maybe 82 F, with maybe 50% humidity. People up there would act like they were melting. OMG it’s so hot!!! This weather must remind you of Texas!!!! How can anybody work in this heat???

If they only knew. 82 F and 50% humidity were winter conditions back home. Jeez.

Himself · May 15, 2024 at 8:01 am

The dewpoint is rarely that high here in DFW. ‘summer’ starts when the temps are in the 80s at 7AM.

But a more informal test would be when walking the dog in the morning wearing jeans and hiking boots turns you into a dishrag. That would be now, BTW.

FormerFlyer · May 15, 2024 at 9:04 pm

When we lived in Northwestern Indiana, near Chicago, the problem was inverted. The 4 seasons were Almost Winter, Winter, Still Winter, and Mosquito Season.

A friend in Arizona points out that most of the country has 2 to 4 months where spending substantial parts of the day outside just sucks. Pick your place, pick your miserable season.

    Divemedic · May 15, 2024 at 9:49 pm

    That’s probably true. California has what is probably the best weather in the country. Too bad it’s run by a granola bar. (Fruits, nuts, and flakes)

      Aesop · May 16, 2024 at 2:29 am

      I can’t do anything to change the weather.
      But if a fraction of the chickenshits who left Califrutopia moved back, we could change who runs it in about one election cycle.

      You can guess how much sympathy I’m going to have for deep purple Texas and Florida when their electoral icebergs flip over in the next few years.

      But whenever it happens, I’ll probably be wearing shorts and a polo shirt, unless it happens during our annual 2 weeks of winter, when I put on a sweatshirt.

      Meanwhile, it’s always seemed stupid to count solistices and equinoxes as the “start” of any season.

      The start of the seasons should be the midpoints between those four dates, IOW about 6½ weeks after each one.

      But then, I’m arguing that common sense proposition with people that still want to keep the horrible anachronism of daylight savings time, which should be killed with fire, and all proponents thereof should have their eyelids cut off and be staked face up all day long for animating that zombie retardation and foisting it on people contrary to any rational discussion in most of the country.

        Divemedic · May 16, 2024 at 6:00 am

        1 Meh. I don’t think elections change anything. Maybe they did, once upon a time. Now, there is no real difference between the Republicans and the Democrats.
        2 Daylight savings is an abomination.
        3 The collapse of the US into something else is inevitable, for no other reason than fiscal irresponsibility. Anyone who can use a calculator sees that.
        4 It’s going to suck. For everyone. Worldwide.

          Aesop · May 17, 2024 at 2:29 am

          If all I get out of that is to kick the people who voted in DST right in the balls, anything else is gravy.

          The difference it would have made hereabouts is the difference between an aircraft making a belly landing with no gear, and one doing a nose dive at terminal velocity into the ground.

          The only good news in that, hereabouts, is that the bigger the crash, the bigger the bonfires, and the faster they pull down the statues of Marx and Lenin afterwards. I’ve earned the right to see that before I die, and Gabbin’ Nuisance is overwhelmingly likely to be the Gorbachev of this particular failed socialist people’s republic.

Exile1981 · May 16, 2024 at 12:11 am

I did 4 months in florida, sep to christmas. Nov/ december were what i was used too temp wise back home…. In july. I was in shorts and the locals had sweaters.

Growing up in northern AB made me not well suited to southern summers.

oldvet50 · May 17, 2024 at 6:38 am

As you might guess, I’m not a fan of this new terminology (dew point v % humidity). It is not easily translated into meaningful info for me. I don’t care what the temp is – if the humidity is near 80%, it is uncomfortable. While dew points may work for describing hot weather, it is sorely lacking for cold. A humid cold is much more uncomfortable than a dry cold. A 38 degree day with 90% humidity is bone chilling – what is the dew point? According to the chart, it should be comfortable. I guess it would be for snowbirds. The only terms I’ve heard about cold weather is ‘chill factor’, but that only combines the wind with the temperature. I’ll take the heat any day – heat may be uncomfortable but cold is painful.

    Divemedic · May 17, 2024 at 8:19 am

    While dew point might be new to you, it isn’t a new concept.

      oldvet50 · May 17, 2024 at 3:22 pm

      I realize that, but it seems that the TV weather reports stopped reporting humidity just this century – that’s new to me. Of course, I cannot understand why an outside temperature of 98.6 F (37 C) isn’t ideal – our bodies shouldn’t have to make its own heat in those conditions.

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