JACKSONVILLE, Fla. – Early season heatwaves are actually fairly common for Northeast Florida and Southeast Georgia. They can happen as early as late April but really tend to get going in May or June.
"Heatwave" has a rather loose definition as an extended period of excessive (abnormally high) temperatures. For me, relative to what we have seen in Jacksonville, it is at least three summer-time days with afternoon highs at or above 95°. Or a string of days with record breaking or near record summer heat.
These stretches of heat can be very impacting on those who work outdoors, the elderly and those without air conditioning. Additionally, early season heatwaves impact everyone harder as we are not yet acustom to the heat.
Possible heatwave for Jacksonville starting next Thursday and lasting for???
The daily record high temperatures for the end of May run between 97° and 99°.
If you glance at the table just note the years, as record heat in Jacksonville tends to come in multiple days of extreme heat.
It was particularly bad in 1953, with three record hot days in a row, each at least 98°. Not shown was that the nighttime/early morning lows were also record warm, averaging about 78°. Basically, there was no relief from the heat. Also note 1985 when we had three days in a row with afternoon highs of 100°.
Average dates for our first
Average first 90° is April 26
Average first 95° is June 2
Average first 100° is June 21, but only happens once every four years on average
Why so hot, so early?
Early season heat waves tend to develop because the sun is very powerful this time of year, even stronger than it is just after the summer solstice. Why? No where to hide from the sun as the atmosphere is much drier and as such we don't tend to have any real possibilities of cooling afternoon clouds or storms.
So there literally is more sunshine and more direct sunshine and without low-levels of moisture in the lower atmosphere conditions rapidly heat up.
Large high pressure areas also create a heat pump for excessive temperatures. The weight of that high pressure compresses air downward and as it sinks, it heats up (this process is called adiabatic heating). The results can be very dramatic as temperatures will leap into the 90s, often times before 10 a.m.
Memorial Day weekend looks to be right up there with daytime highs likely to be 95° or hotter.
A number of raw forecasts produced by the two main forecast models (the GFS and the EURO) are suggesting highs could reach above 100° in May!
This has never happened before as the earliest 100° day in Jacksonville, was 100° on June 2, 1985.
Stay up to date and check back for more on this developing weather story.